1
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Franca L, Danos A, Saxena R, Kuila S, Stavrou K, Li C, Wedler S, Köhler A, Monkman AP. Exploring the Early Time Behavior of the Excited States of an Archetype Thermally Activated Delayed Fluorescence Molecule. J Phys Chem Lett 2024; 15:1734-1740. [PMID: 38323906 PMCID: PMC10875657 DOI: 10.1021/acs.jpclett.4c00030] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2024] [Revised: 01/30/2024] [Accepted: 02/02/2024] [Indexed: 02/08/2024]
Abstract
Optical pump-probe techniques allow for an in-depth study of dark excited states. Here, we utilize them to map and gain insights into the excited states involved in the thermally activated delayed fluorescence (TADF) mechanism of a benchmark TADF emitter DMAC-TRZ. The results identify different electronic excited states involved in the key TADF transitions and their nature by combining pump-probe and photoluminescence measurements. The photoinduced absorption signals are highly dependent on polarity, affecting the transition oscillator strength but not their relative energy positions. In methylcyclohexane, a strong and vibronically structured local triplet excited state absorption (3LE → 3LEn) is observed, which is quenched in higher polarity solvents as 3CT becomes the lowest triplet state. Furthermore, ultrafast transient absorption (fsTA) confirms the presence of two stable conformers of DMAC-TRZ: (1) quasi-axial (QA) interconverting within 20 ps into (2) quasi-equatorial (QE) in the excited state. Moreover, fsTA highlights how sensitive excited state couplings are to the environment and the molecular conformation.
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Affiliation(s)
- Larissa
G. Franca
- Department
of Physics, Durham University, South Road, Durham DH13LE, United Kingdom
| | - Andrew Danos
- Department
of Physics, Durham University, South Road, Durham DH13LE, United Kingdom
| | - Rishabh Saxena
- Soft
Matter Optoelectronics and Bavarian Polymer Institute (BPS), University of Bayreuth, Universitätsstrasse 30, Bayreuth 95440, Germany
| | - Suman Kuila
- Department
of Physics, Durham University, South Road, Durham DH13LE, United Kingdom
| | - Kleitos Stavrou
- Department
of Physics, Durham University, South Road, Durham DH13LE, United Kingdom
| | - Chunyong Li
- Department
of Physics, Durham University, South Road, Durham DH13LE, United Kingdom
| | - Stefan Wedler
- Soft
Matter Optoelectronics and Bavarian Polymer Institute (BPS), University of Bayreuth, Universitätsstrasse 30, Bayreuth 95440, Germany
| | - Anna Köhler
- Soft
Matter Optoelectronics and Bavarian Polymer Institute (BPS), University of Bayreuth, Universitätsstrasse 30, Bayreuth 95440, Germany
| | - Andrew P. Monkman
- Department
of Physics, Durham University, South Road, Durham DH13LE, United Kingdom
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2
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Paredis S, Cardeynaels T, Brebels S, Deckers J, Kuila S, Lathouwers A, Van Landeghem M, Vandewal K, Danos A, Monkman AP, Champagne B, Maes W. Intramolecular locking and coumarin insertion: a stepwise approach for TADF design. Phys Chem Chem Phys 2023; 25:29842-29849. [PMID: 37888766 DOI: 10.1039/d3cp03695b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2023]
Abstract
Three novel TADF (thermally activated delayed fluorescence) emitters based on the well-studied Qx-Ph-DMAC fluorophore are designed and synthesized. The photophysical properties of these materials are studied from a theoretical and experimental point of view, demonstrating the cumulative effects of multiple small modifications that combine to afford significantly improved TADF performance. First, an extra phenyl ring is added to the acceptor part of Qx-Ph-DMAC to increase the conjugation length, resulting in BQx-Ph-DMAC, which acts as an intermediate molecular structure. Next, an electron-deficient coumarin unit is incorporated to fortify the electron accepting ability, affording ChromPy-Ph-DMAC with red-shifted emission. Finally, the conjugated system is further enlarged by 'locking' the molecular structure, generating DBChromQx-DMAC with further red-shifted emission. The addition of the coumarin unit significantly impacts the charge-transfer excited state energy levels with little effect on the locally excited states, resulting in a decrease of the singlet-triplet energy gap. As a result, the two coumarin-based emitters show considerably improved TADF performance in 1 w/w% zeonex films when compared to the initial Qx-Ph-DMAC structure. 'Locking' the molecular structure further lowers the singlet-triplet energy gap, resulting in more efficient reverse intersystem crossing and increasing the contribution of TADF to the total emission.
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Affiliation(s)
- S Paredis
- Hasselt University, Institute for Materials Research (IMO-IMOMEC), Design & Synthesis of Organic Semiconductors (DSOS), Agoralaan 1, Diepenbeek 3590, Belgium.
- IMOMEC Division, IMEC, Wetenschapspark 1, Diepenbeek 3590, Belgium
- Energyville, Thorpark, Genk 3600, Belgium
| | - T Cardeynaels
- Hasselt University, Institute for Materials Research (IMO-IMOMEC), Design & Synthesis of Organic Semiconductors (DSOS), Agoralaan 1, Diepenbeek 3590, Belgium.
- IMOMEC Division, IMEC, Wetenschapspark 1, Diepenbeek 3590, Belgium
- Energyville, Thorpark, Genk 3600, Belgium
- University of Namur, Laboratory of Theoretical Chemistry, Theoretical and Structural Physical Chemistry Unit, Namur Institute of Structured Matter, Rue de Bruxelles 61, Namur 5000, Belgium
| | - S Brebels
- Hasselt University, Institute for Materials Research (IMO-IMOMEC), Design & Synthesis of Organic Semiconductors (DSOS), Agoralaan 1, Diepenbeek 3590, Belgium.
- IMOMEC Division, IMEC, Wetenschapspark 1, Diepenbeek 3590, Belgium
- Energyville, Thorpark, Genk 3600, Belgium
| | - J Deckers
- Hasselt University, Institute for Materials Research (IMO-IMOMEC), Design & Synthesis of Organic Semiconductors (DSOS), Agoralaan 1, Diepenbeek 3590, Belgium.
- IMOMEC Division, IMEC, Wetenschapspark 1, Diepenbeek 3590, Belgium
- Energyville, Thorpark, Genk 3600, Belgium
| | - S Kuila
- Durham University, Department of Physics, OEM Group, South Road, Durham DH1 3LE, UK.
| | - A Lathouwers
- Hasselt University, Institute for Materials Research (IMO-IMOMEC), Design & Synthesis of Organic Semiconductors (DSOS), Agoralaan 1, Diepenbeek 3590, Belgium.
- IMOMEC Division, IMEC, Wetenschapspark 1, Diepenbeek 3590, Belgium
- Energyville, Thorpark, Genk 3600, Belgium
| | - M Van Landeghem
- IMOMEC Division, IMEC, Wetenschapspark 1, Diepenbeek 3590, Belgium
- Energyville, Thorpark, Genk 3600, Belgium
- Hasselt University, Institute for Materials Research (IMO-IMOMEC), Organic Opto-Electronics (OOE), Wetenschapspark 1, Diepenbeek 3590, Belgium
| | - K Vandewal
- IMOMEC Division, IMEC, Wetenschapspark 1, Diepenbeek 3590, Belgium
- Energyville, Thorpark, Genk 3600, Belgium
- Hasselt University, Institute for Materials Research (IMO-IMOMEC), Organic Opto-Electronics (OOE), Wetenschapspark 1, Diepenbeek 3590, Belgium
| | - A Danos
- Durham University, Department of Physics, OEM Group, South Road, Durham DH1 3LE, UK.
| | - A P Monkman
- Durham University, Department of Physics, OEM Group, South Road, Durham DH1 3LE, UK.
| | - B Champagne
- University of Namur, Laboratory of Theoretical Chemistry, Theoretical and Structural Physical Chemistry Unit, Namur Institute of Structured Matter, Rue de Bruxelles 61, Namur 5000, Belgium
| | - W Maes
- Hasselt University, Institute for Materials Research (IMO-IMOMEC), Design & Synthesis of Organic Semiconductors (DSOS), Agoralaan 1, Diepenbeek 3590, Belgium.
- IMOMEC Division, IMEC, Wetenschapspark 1, Diepenbeek 3590, Belgium
- Energyville, Thorpark, Genk 3600, Belgium
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3
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Salah L, Makhseed S, Ghazal B, Abdel Nazeer A, Etherington MK, Ponseca CS, Li C, Monkman AP, Danos A, Shuaib A. Covalently linked pyrene antennas for optically dense yet aggregation-resistant light-harvesting systems. Phys Chem Chem Phys 2023; 25:24878-24882. [PMID: 37681234 DOI: 10.1039/d3cp02586a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/09/2023]
Abstract
In this study we present a novel energy transfer material inspired by natural light-harvesting antenna arrays, zinc(II) phthalocyanine-pyrene (ZnPcPy). The ZnPcPy system facilitates energy transfer from 16 covalently linked pyrene (Py) donor chromophores to the emissive central zinc(II) phthalocyanine (ZnPc) core. Nearly 98% energy transfer efficiency is determined from the changes in emission decay rates between free MePy to covalently linked Py, supported by comparisons of photoluminescence quantum yields using different excitation wavelengths. A comparative analysis of ZnPcPy and an equivalent mixture of ZnPc and MePy demonstrates the superior light-harvesting performance of the covalently linked system, with energy transfer rates 9705 times higher in the covalently bound system. This covalent strategy allows for very high loadings of absorbing Py chromophores to be achieved while also avoiding exciton quenching that would otherwise arise, with the same strategy widely applicable to other pairs of Főrster resonance energy transfer (FRET) chromophores.
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Affiliation(s)
- Lubna Salah
- Department of Chemistry, Faculty of Science, Kuwait University, P. O. Box 5969, Safat 13060, Kuwait
| | - Saad Makhseed
- Department of Chemistry, Faculty of Science, Kuwait University, P. O. Box 5969, Safat 13060, Kuwait
| | - Basma Ghazal
- Organometallic and Organometalloid Chemistry Department, National Research Centre, Giza, Egypt
| | - Ahmed Abdel Nazeer
- Organometallic and Organometalloid Department, National Research Centre, Dokki, Cairo, 12622, Egypt
| | - Marc K Etherington
- Department of Mathematics, Physics & Electrical Engineering, Northumbria University, Ellison Place, Newcastle upon Tyne, NE1 8ST, UK
| | - Carlito S Ponseca
- Mathematics and Natural Science Department, Gulf University for Science and Technology, Kuwait
| | - Chunyong Li
- Department of Physics, Durham University, South Road, Durham, DH1 3LE, UK.
| | - Andrew P Monkman
- Department of Physics, Durham University, South Road, Durham, DH1 3LE, UK.
| | - Andrew Danos
- Department of Physics, Durham University, South Road, Durham, DH1 3LE, UK.
| | - Ali Shuaib
- Biomedical Engineering Unit, Department of Physiology, Faculty of Medicine, Kuwait University, P. O. Box 24923, Safat 13110, Kuwait.
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4
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Wright IA, Etherington MK, Batsanov AS, Monkman AP, Bryce MR. Oxidation State Tuning of Room Temperature Phosphorescence and Delayed Fluorescence in Phenothiazine and Phenothiazine-5,5-dioxide Dimers. Chemistry 2023; 29:e202300428. [PMID: 36916635 PMCID: PMC10946842 DOI: 10.1002/chem.202300428] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2023] [Revised: 03/10/2023] [Accepted: 03/13/2023] [Indexed: 03/16/2023]
Abstract
Heterocyclic dimers consisting of combinations of butterfly-shaped phenothiazine (PTZ) and its chemically oxidized form phenothiazine-5,5-dioxide (PTZ(SO2 )) have been synthesized. A twist is imposed across the dimers by ortho-substituents including methyl ethers, sulfides and sulfones. X-ray crystallography, cyclic voltammetry and optical spectroscopy, underpinned by computational studies, have been employed to study the interplay between the oxidation state, conformational restriction, and emission mechanisms including thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP). While the PTZ(SO2 ) dimers are simple fluorophores, the presence of PTZ induces triplet-mediated emission with a mixed PTZ-PTZ(SO2 ) dimer displaying concentration dependent hallmarks of both TADF and RTP.
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Affiliation(s)
- Iain A. Wright
- Department of ChemistryDurham UniversitySouth RoadDurhamDH1 3LEUK
- School of ChemistryUniversity of EdinburghDavid Brewster RoadEdinburghEH9 3FJUK
| | - Marc K. Etherington
- Department of PhysicsDurham UniversitySouth RoadDurhamDH1 3LEUK
- Department of Mathematics, Physics and Electrical EngineeringNorthumbria UniversityEllison PlaceNewcastle upon TyneNE1 8STUK
| | | | | | - Martin R. Bryce
- Department of ChemistryDurham UniversitySouth RoadDurhamDH1 3LEUK
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5
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Miranda-Salinas H, Rodriguez-Serrano A, Kaminski JM, Dinkelbach F, Hiromichi N, Kusakabe Y, Kaji H, Marian CM, Monkman AP. Conformational, Host, and Vibrational Effects Giving Rise to Dynamic TADF Behavior in the Through-Space Charge Transfer, Triptycene Bridged Acridine-Triazine Donor Acceptor TADF Molecule TpAT-tFFO. J Phys Chem C Nanomater Interfaces 2023; 127:8607-8617. [PMID: 37197385 PMCID: PMC10184167 DOI: 10.1021/acs.jpcc.2c07529] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/26/2022] [Revised: 04/12/2023] [Indexed: 05/19/2023]
Abstract
We present a joint experimental and theoretical study of the through-space charge transfer (CT) TADF molecule TpAT-tFFO. The measured fluorescence has a singular Gaussian line shape but two decay components, coming from two distinct molecular CT conformers, energetically only 20 meV apart. We determined the intersystem crossing rate (1 × 107 s-1) to be 1 order of magnitude faster than radiative decay, and prompt emission (PF) is therefore quenched within 30 ns, leaving delayed fluorescence (DF) observable from 30 ns onward as the measured reverse intersystem crossing (rISC) rate is >1 × 106 s-1, yielding a DF/PF ratio >98%. Time-resolved emission spectra measured between 30 ns and 900 ms in films show no change in the spectral band shape, but between 50 and 400 ms, we observe a ca. 65 meV red shift of the emission, ascribed to the DF to phosphorescence transition, with the phosphorescence (lifetime >1 s) emanating from the lowest 3CT state. A host-independent thermal activation energy of 16 meV is found, indicating that small-amplitude vibrational motions (∼140 cm-1) of the donor with respect to the acceptor dominate rISC. TpAT-tFFO photophysics is dynamic, and these vibrational motions drive the molecule between maximal rISC rate and high radiative decay configurations so that the molecule can be thought to be "self-optimizing" for the best TADF performance.
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Affiliation(s)
| | - Angela Rodriguez-Serrano
- Institut
für Theoretische Chemie und Computerchemie, Heinrich-Heine-Universität
Düsseldorf, Universitätsstraße 1, D-40225 Düsseldorf, Germany
| | - Jeremy M. Kaminski
- Institut
für Theoretische Chemie und Computerchemie, Heinrich-Heine-Universität
Düsseldorf, Universitätsstraße 1, D-40225 Düsseldorf, Germany
| | - Fabian Dinkelbach
- Institut
für Theoretische Chemie und Computerchemie, Heinrich-Heine-Universität
Düsseldorf, Universitätsstraße 1, D-40225 Düsseldorf, Germany
| | - Nakagawa Hiromichi
- Institute
for Chemical Research Kyoto University, Uji, Kyoto 611-0011, Japan
| | - Yu Kusakabe
- Institute
for Chemical Research Kyoto University, Uji, Kyoto 611-0011, Japan
| | - Hironori Kaji
- Institute
for Chemical Research Kyoto University, Uji, Kyoto 611-0011, Japan
| | - Christel M. Marian
- Institut
für Theoretische Chemie und Computerchemie, Heinrich-Heine-Universität
Düsseldorf, Universitätsstraße 1, D-40225 Düsseldorf, Germany
| | - Andrew P. Monkman
- OEM
Research Group, Department of Physics, Durham
University, Durham DH1 3LE, UK
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6
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Paredis S, Cardeynaels T, Kuila S, Deckers J, Van Landeghem M, Vandewal K, Danos A, Monkman AP, Champagne B, Maes W. Balanced Energy Gaps as a Key Design Rule for Solution-Phase Organic Room Temperature Phosphorescence. Chemistry 2023:e202301369. [PMID: 37154211 DOI: 10.1002/chem.202301369] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2023] [Revised: 05/03/2023] [Accepted: 05/08/2023] [Indexed: 05/10/2023]
Abstract
Metal-free organic emitters that display solution-phase room temperature phosphorescence (sRTP) remain exceedingly rare. Here, we investigate the structural and photophysical properties that support sRTP by comparing a recently reported sRTP compound (BTaz-Th-PXZ) to two novel analogous materials, replacing the donor group by either acridine or phenothiazine. The emissive triplet excited state remains fixed in all three cases, while the emissive charge-transfer singlet states (and the calculated paired charge-transfer T2 state) vary with the donor unit. While all three materials show dominant RTP in film, in solution different singlet-triplet and triplet-triplet energy gaps give rise to triplet-triplet annihilation followed by weak sRTP for the new compounds, compared to dominant sRTP throughout for the original PXZ material. Engineering both the sRTP state and higher charge-transfer states therefore emerges as a crucial element in designing emitters capable of sRTP.
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Affiliation(s)
- Simon Paredis
- Hasselt University: Universiteit Hasselt, Chemistry, BELGIUM
| | - Tom Cardeynaels
- Hasselt University: Universiteit Hasselt, Chemistry, BELGIUM
| | | | - Jasper Deckers
- Hasselt University: Universiteit Hasselt, Chemistry, BELGIUM
| | | | - Koen Vandewal
- Hasselt University: Universiteit Hasselt, Physics, Wetenschapspark 1, 3590, Diepenbeek, BELGIUM
| | | | | | | | - Wouter Maes
- Institute for Materials Research IMO-IMOMEC , Hasselt University, Design & Synthesis of Organic Semiconductors DSOS, Univ. Campus, Agoralaan 1 - Building D, 3590, Diepenbeek, BELGIUM
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7
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Saha PK, Mallick A, Turley AT, Bismillah AN, Danos A, Monkman AP, Avestro AJ, Yufit DS, McGonigal PR. Rupturing aromaticity by periphery overcrowding. Nat Chem 2023; 15:516-525. [PMID: 36879076 PMCID: PMC10070187 DOI: 10.1038/s41557-023-01149-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2022] [Accepted: 01/26/2023] [Indexed: 03/08/2023]
Abstract
The balance between strain relief and aromatic stabilization dictates the form and function of non-planar π-aromatics. Overcrowded systems are known to undergo geometric deformations, but the energetically favourable π-electron delocalization of their aromatic ring(s) is typically preserved. In this study we incremented the strain energy of an aromatic system beyond its aromatic stabilization energy, causing it to rearrange and its aromaticity to be ruptured. We noted that increasing the steric bulk around the periphery of π-extended tropylium rings leads them to deviate from planarity to form contorted conformations in which aromatic stabilization and strain are close in energy. Under increasing strain, the aromatic π-electron delocalization of the system is broken, leading to the formation of a non-aromatic, bicyclic analogue referred to as 'Dewar tropylium'. The aromatic and non-aromatic isomers have been found to exist in rapid equilibrium with one another. This investigation demarcates the extent of steric deformation tolerated by an aromatic carbocycle and thus provides direct experimental insights into the fundamental nature of aromaticity.
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Affiliation(s)
| | | | | | | | - Andrew Danos
- Department of Physics, Durham University, Durham, UK
| | | | | | | | - Paul R McGonigal
- Department of Chemistry, Durham University, Durham, UK.
- Department of Chemistry, University of York, York, UK.
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8
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Urban M, Marek-Urban PH, Durka K, Luliński S, Pander P, Monkman AP. TADF Invariant of Host Polarity and Ultralong Fluorescence Lifetimes in a Donor-Acceptor Emitter Featuring a Hybrid Sulfone-Triarylboron Acceptor. Angew Chem Int Ed Engl 2023; 62:e202217530. [PMID: 36622736 DOI: 10.1002/anie.202217530] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2022] [Revised: 01/08/2023] [Accepted: 01/09/2023] [Indexed: 01/10/2023]
Abstract
10H-Dibenzo[b,e][1,4]thiaborinine 5,5-dioxide (SO2B)-a high triplet (T1 =3.05 eV) strongly electron-accepting boracycle was successfully utilised in thermally activated delayed fluorescence (TADF) emitters PXZ-Dipp-SO2B and CZ-Dipp-SO2B. We demonstrate the near-complete separation of highest occupied and lowest unoccupied molecular orbitals leading to a low oscillator strength of the S1 →S0 CT transition, resulting in very long ca. 83 ns and 400 ns prompt fluorescence lifetimes for CZ-Dipp-SO2B and PXZ-Dipp-SO2B, respectively, but retaining near unity photoluminescence quantum yield. OLEDs using CZ-Dipp-SO2B as the luminescent dopant display high external quantum efficiency (EQE) of 23.3 % and maximum luminance of 18600 cd m-2 with low efficiency roll off at high brightness. For CZ-Dipp-SO2B, reverse intersystem crossing (rISC) is mediated through the vibronic coupling of two charge transfer (CT) states, without involving the triplet local excited state (3 LE), resulting in remarkable rISC rate invariance to environmental polarity and polarisability whilst giving high organic light-emitting diode (OLED) efficiency. This new form of rISC allows stable OLED performance to be achieved in different host environments.
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Affiliation(s)
- Mateusz Urban
- Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664, Warsaw, Poland.,Department of Physics, Durham University, South Road, Durham, DH1 3LE, UK
| | - Paulina H Marek-Urban
- Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664, Warsaw, Poland
| | - Krzysztof Durka
- Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664, Warsaw, Poland
| | - Sergiusz Luliński
- Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664, Warsaw, Poland
| | - Piotr Pander
- Faculty of Chemistry, Silesian University of Technology, Strzody 9, 44-100, Gliwice, Poland.,Department of Physics, Durham University, South Road, Durham, DH1 3LE, UK
| | - Andrew P Monkman
- Department of Physics, Durham University, South Road, Durham, DH1 3LE, UK
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9
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Marchi Luciano H, Farias G, Salla CM, Franca LG, Kuila S, Monkman AP, Durola F, Bechtold IH, Bock H, Gallardo H. Room Temperature Phosphorescence in Solution from Thiophene-Bridged Triply Donor-Substituted Tristriazolotriazines. Chemistry 2023; 29:e202203800. [PMID: 36648938 DOI: 10.1002/chem.202203800] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2022] [Revised: 01/17/2023] [Accepted: 01/17/2023] [Indexed: 01/18/2023]
Abstract
Most organic room-temperature phosphorescence (RTP) emitters do not show their RTP in solution. Here, we incorporated sulfur-containing thiophene bridges between the donor and acceptor moieties in D3 A-type tristriazolotriazines (TTTs). The thiophene inclusion increased the spin-orbit coupling associated with the radiative T1 →S0 pathway, allowing RTP to be observed in solution for all compounds, likely assisted by protection of the emissive TTT-thiophene core from the environment by the bulky peripheral donors.
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Affiliation(s)
- Hugo Marchi Luciano
- Departamento de Química, Universidade Federal de Santa Catarina Trindade, 88040-900, Florianópolis, SC, Brazil.,Centre de Recherche Paul Pascal, Université Bordeaux, 115 av. Schweitzer, 33600, Pessac, France
| | - Giliandro Farias
- Departamento de Química, Universidade Federal de Santa Catarina Trindade, 88040-900, Florianópolis, SC, Brazil
| | - Cristian M Salla
- Departamento de Física, Universidade Federal de Santa Catarina Trindade, 88040-900, Florianópolis, SC, Brazil
| | | | - Suman Kuila
- Department of Physics, Durham University, Durham, DH1 3LE, UK
| | | | - Fabien Durola
- Centre de Recherche Paul Pascal, CNRS, 115 av. Schweitzer, 33600, Pessac, France
| | - Ivan H Bechtold
- Departamento de Física, Universidade Federal de Santa Catarina Trindade, 88040-900, Florianópolis, SC, Brazil
| | - Harald Bock
- Centre de Recherche Paul Pascal, CNRS, 115 av. Schweitzer, 33600, Pessac, France
| | - Hugo Gallardo
- Departamento de Química, Universidade Federal de Santa Catarina Trindade, 88040-900, Florianópolis, SC, Brazil
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10
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Urban M, Marek-Urban PH, Durka KK, Luliński S, Pander P, Monkman AP. TADF Invariant of Host Polarity and Ultralong Fluorescence Lifetimes in a Donor–Acceptor Emitter Featuring a Hybrid Sulfone–Triarylboron Acceptora. Angew Chem Int Ed Engl 2023. [DOI: 10.1002/ange.202217530] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Affiliation(s)
- Mateusz Urban
- Warsaw University of Technology: Politechnika Warszawska Faculty of Chemistry Noakowskiego 3 00-664 Warsaw POLAND
| | - Paulina H. Marek-Urban
- Warsaw University of Technology: Politechnika Warszawska Faculty of Chemistry 00-664 Warsaw POLAND
| | - Krzysztof Konrad Durka
- Warsaw University of Technology: Politechnika Warszawska Faculty of Chemistry Noakowskiego 3 00-664 Warsaw POLAND
| | - Sergiusz Luliński
- Warsaw University of Technology: Politechnika Warszawska Faculty of Chemistry Noakowskiego 3 00-664 Warsaw POLAND
| | - Piotr Pander
- Durham University Department of Physics South Road DH1 3LE Durham POLAND
| | - Andrew P. Monkman
- Durham University Department of Physics South Road DH1 3LE Durham POLAND
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11
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Salla CAM, Farias G, Sturm L, Dechambenoit P, Durola F, Murat A, de Souza B, Bock H, Monkman AP, Bechtold IH. The effect of substituents and molecular aggregation on the room temperature phosphorescence of a twisted π-system. Phys Chem Chem Phys 2023; 25:684-689. [DOI: 10.1039/d2cp04658j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Room temperature phosphorescence of an intrinsically apolar twisted π-system is modulated by polar substituents. Persistent phosphorescence is visible by eye in poder, induced by molecular aggregation.
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Affiliation(s)
- Cristian A. M. Salla
- Department of Physics, Universidade Federal de Santa Catarina, 88040-900 Florianópolis, SC, Brazil
| | - Giliandro Farias
- Department of Chemistry, Universidade Federal de Santa Catarina, 88040-900 Florianópolis, SC, Brazil
| | - Ludmilla Sturm
- Centre de Recherche Paul Pascal, CNRS & Université de Bordeaux, 115, av. Schweitzer, 33600 Pessac, France
| | - Pierre Dechambenoit
- Centre de Recherche Paul Pascal, CNRS & Université de Bordeaux, 115, av. Schweitzer, 33600 Pessac, France
| | - Fabien Durola
- Centre de Recherche Paul Pascal, CNRS & Université de Bordeaux, 115, av. Schweitzer, 33600 Pessac, France
| | - Aydemir Murat
- Department of Physics, Durham University, South Road, Durham, DH1 3LE, UK
- Erzurum Technical University, Department of Fundamental Sciences, Erzurum, Turkey
| | - Bernardo de Souza
- Department of Chemistry, Universidade Federal de Santa Catarina, 88040-900 Florianópolis, SC, Brazil
| | - Harald Bock
- Centre de Recherche Paul Pascal, CNRS & Université de Bordeaux, 115, av. Schweitzer, 33600 Pessac, France
| | - Andrew P. Monkman
- Department of Physics, Durham University, South Road, Durham, DH1 3LE, UK
| | - Ivan H. Bechtold
- Department of Physics, Universidade Federal de Santa Catarina, 88040-900 Florianópolis, SC, Brazil
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12
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dos Santos PL, de Sa Pereira D, Eng J, Ward JS, Bryce MR, Penfold TJ, Monkman AP. Fine tuning the Photophysics of Donor‐Acceptor (D‐A3) Thermally Activated Delayed Fluorescence Emitters Using Isomerisation. CHEMPHOTOCHEM 2022. [DOI: 10.1002/cptc.202200248] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | - Daniel de Sa Pereira
- Durham University Physics South Road, Durham University DH1 3LE Durham UNITED KINGDOM
| | - Julien Eng
- Newcastle University School of Natural and Environmental Sciences NE1 7RU Newcastle UNITED KINGDOM
| | - Jonathan S. Ward
- University of Liverpool Chemistry Crown St L69 7ZD Liverpool UNITED KINGDOM
| | | | - Thomas J. Penfold
- Newcastle University Chemistry School of Natural and Environmental Sciences NE1 7RU Newcastle UNITED KINGDOM
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13
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Hempe M, Kukhta NA, Danos A, Batsanov AS, Monkman AP, Bryce MR. Intramolecular Hydrogen Bonding in Thermally Activated Delayed Fluorescence Emitters: Is There Evidence Beyond Reasonable Doubt? J Phys Chem Lett 2022; 13:8221-8227. [PMID: 36007139 PMCID: PMC9465681 DOI: 10.1021/acs.jpclett.2c00907] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Intramolecular hydrogen bonding between donor and acceptor segments in thermally activated delayed fluorescence (TADF) materials is now frequently employed to─purportedly─rigidify the structure and improve the emission performance of these materials. However, direct evidence for these intramolecular interactions is often lacking or ambiguous, leading to assertions that are largely speculative. Here we investigate a series of TADF-active materials incorporating pyridine, which bestows the potential ability to form intramolecular H-bonding interactions. Despite possible indications of H-bonding from an X-ray analysis, an array of other experimental investigations proved largely inconclusive. Instead, after examining computational potential energy surfaces of the donor-acceptor torsion angle we conclude that the pyridine group primarily alleviates steric congestion in our case, rather than enabling an H-bond interaction as elsewhere assumed. We suggest that many previously reported "H-bonding" TADF materials featuring similar chemical motifs may instead operate similarly and that investigation of potential energy surfaces should become a key feature of future studies.
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Affiliation(s)
- Matthias Hempe
- Chemistry
Department, Durham University, South Road, Durham DH1 3LE, U.K.
| | - Nadzeya A. Kukhta
- Chemistry
Department, Durham University, South Road, Durham DH1 3LE, U.K.
- Materials
Science and Engineering Department, University
of Washington, Seattle, Washington 98195, United States
| | - Andrew Danos
- Physics
Department, Durham University, South Road, Durham, DH1 3LE, U.K.
| | - Andrei S. Batsanov
- Chemistry
Department, Durham University, South Road, Durham DH1 3LE, U.K.
| | - Andrew P. Monkman
- Physics
Department, Durham University, South Road, Durham, DH1 3LE, U.K.
| | - Martin R. Bryce
- Chemistry
Department, Durham University, South Road, Durham DH1 3LE, U.K.
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14
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Kelly D, Franca LG, Stavrou K, Danos A, Monkman AP. Laplace Transform Fitting as a Tool To Uncover Distributions of Reverse Intersystem Crossing Rates in TADF Systems. J Phys Chem Lett 2022; 13:6981-6986. [PMID: 35881847 PMCID: PMC9358706 DOI: 10.1021/acs.jpclett.2c01864] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2022] [Accepted: 07/18/2022] [Indexed: 05/22/2023]
Abstract
Donor-acceptor (D-A) thermally activated delayed fluorescence (TADF) molecules are exquisitely sensitive to D-A dihedral angle. Although commonly simplified to an average value, these D-A angles nonetheless exist as distributions across the individual molecules embedded in films. The presence of these angle distributions translates to distributions in the rates of reverse intersystem crossing (krISC), observed as time dependent spectral shifts and multiexponential components in the emission decay, which are difficult to directly quantify. Here we apply inverse Laplace transform fitting of delayed fluorescence to directly reveal these distributions. Rather than a single average value, the crucial krISC rate is instead extracted as a density of rates. The modes and widths of these distributions vary with temperature, host environment, and intrinsic D-A torsional rigidity of different TADF molecules. This method gives new insights and deeper understanding of TADF host-guest interactions, as well as verifies future design strategies that target D-A bond rigidity.
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15
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Maggiore A, Tan X, Brosseau A, Danos A, Miomandre F, Monkman AP, Audebert P, Clavier G. Novel D-A chromophores with condensed 1,2,4-triazine system simultaneously display thermally activated delayed fluorescence and crystallization-induced phosphorescence. Phys Chem Chem Phys 2022; 24:17770-17781. [PMID: 35848596 DOI: 10.1039/d2cp00777k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Control of photophysical properties is crucial for the continued development of electroluminescent devices and luminescent materials. Preparation and study of original molecules uncovers design rules towards efficient materials and devices. Here we have prepared 7 new compounds based on the popular donor-acceptor design used in thermally activated delayed fluorescence emitters. We introduce for the first time benzofuro[3,2-e]-1,2,4-triazine and benzothieno[3,2-e]-1,2,4-triazine acceptors which were connected to several common donors: phenoxazine, phenothiazine, carbazole and 3,6-di-tert-butylcarbazole. DFT calculations, and steady-state and time-resolved photophysical studies were conducted in solution and in solid states. While derivatives with azine moieties are non-emissive in any form, the compounds comprising 3,6-di-tert-butylcarbazole display TADF in all cases. More interestingly, the two derivatives substituted with a carbazole donor are TADF active when dispersed in a polymer matrix and phosphorescent at room temperature in neat films (microcrystalline form).
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Affiliation(s)
- Antonio Maggiore
- Université Paris-Saclay, ENS Paris-Saclay, CNRS, PPSM, 91190 Gif-sur-Yvette, France. .,CNR-NANOTEC - Institute of Nanotechnology, c/o Campus Ecoteckne, Via Monteroni, 73100 Lecce, Italy
| | - Xiaofeng Tan
- Department of Polymer Chemistry and Technology, Kaunas University of Technology, Radvilenu plentas 19, LT50254 Kaunas, Lithuania
| | - Arnaud Brosseau
- Université Paris-Saclay, ENS Paris-Saclay, CNRS, PPSM, 91190 Gif-sur-Yvette, France.
| | - Andrew Danos
- Physics Department, Durham University, Durham DH1 3LE, UK
| | - Fabien Miomandre
- Université Paris-Saclay, ENS Paris-Saclay, CNRS, PPSM, 91190 Gif-sur-Yvette, France.
| | | | - Pierre Audebert
- Université Paris-Saclay, ENS Paris-Saclay, CNRS, PPSM, 91190 Gif-sur-Yvette, France.
| | - Gilles Clavier
- Université Paris-Saclay, ENS Paris-Saclay, CNRS, PPSM, 91190 Gif-sur-Yvette, France.
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16
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Franca LG, dos Santos PL, Pander P, Cabral MB, Cristiano R, Cazati T, Monkman AP, Bock H, Eccher J. Delayed Fluorescence by Triplet-Triplet Annihilation from Columnar Liquid Crystal Films. ACS Appl Electron Mater 2022; 4:3486-3494. [PMID: 35910938 PMCID: PMC9330766 DOI: 10.1021/acsaelm.2c00432] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Delayed fluorescence (DF) by triplet-triplet annihilation (TTA) is observed in solutions of a benzoperylene-imidoester mesogen that shows a hexagonal columnar mesophase at room temperature in the neat state. A similar benzoperylene-imide with a slightly smaller HOMO-LUMO gap, that also is hexagonal columnar liquid crystalline at room temperature, does not show DF in solution, and mixtures of the two mesogens show no DF in solution either, because of collisional quenching of the excited triplet states on the imidoester by the imide. In contrast, DF by TTA from the imide but not from the imidoester is observed in condensed films of such mixtures, even though neat films of either single material are not displaying DF. In contrast to the DF from the monomeric imidoester in solution, DF of the imide occurs from dimeric aggregates in the blend films, assisted by the imidoester. Thus, the close contact of intimately stacked molecules of the two different species in the columnar mesophase leads to a unique mesophase-assisted aggregate DF. This constitutes the first observation of DF by TTA from the columnar liquid crystalline state. If the imide is dispersed in films of polybromostyrene, which provides an external heavy-atom effect facilitating triplet formation, DF is also observed. Organic light-emitting diodes (OLEDs) devices incorporating these liquid crystal molecules demonstrated high external quantum efficiency (EQE). On the basis of the literature and to the best of our knowledge, the EQE reported is the highest among nondoped solution-processed OLED devices using a columnar liquid crystal molecule as the emitting layer.
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Affiliation(s)
- Larissa G. Franca
- Department
of Physics, Durham University, South Road, Durham, DH1 3LE, United
Kingdom
- Departamento
de Física, Universidade Federal de
Santa Catarina, 88040900, Florianópolis, Santa Catarina, Brazil
| | - Paloma L. dos Santos
- Department
of Physics, Durham University, South Road, Durham, DH1 3LE, United
Kingdom
| | - Piotr Pander
- Department
of Physics, Durham University, South Road, Durham, DH1 3LE, United
Kingdom
- Faculty
of Chemistry, Silesian University of Technology, Strzody 9, 44-100 Gliwice, Poland
| | - Marília
G. B. Cabral
- Departamento
de Química, Universidade Federal
da Paraíba, CEP 58051-900, João Pessoa, Paraíba, Brazil
- Centre
de Recherche Paul-Pascal, CNRS & Université
de Bordeaux, 33600, Pessac, France
| | - Rodrigo Cristiano
- Departamento
de Química, Universidade Federal
da Paraíba, CEP 58051-900, João Pessoa, Paraíba, Brazil
| | - Thiago Cazati
- Departamento
de Física, Universidade Federal de
Ouro Preto − UFOP, 35400-000, Ouro Preto, Minas
Gerais, Brazil
| | - Andrew P. Monkman
- Department
of Physics, Durham University, South Road, Durham, DH1 3LE, United
Kingdom
| | - Harald Bock
- Centre
de Recherche Paul-Pascal, CNRS & Université
de Bordeaux, 33600, Pessac, France
| | - Juliana Eccher
- Departamento
de Física, Universidade Federal de
Santa Catarina, 88040900, Florianópolis, Santa Catarina, Brazil
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17
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Turley AT, Saha PK, Danos A, Bismillah AN, Monkman AP, Yufit DS, Curchod BFE, Etherington MK, McGonigal PR. Extended Conjugation Attenuates the Quenching of Aggregation-Induced Emitters by Photocyclization Pathways. Angew Chem Int Ed Engl 2022; 61:e202202193. [PMID: 35343025 PMCID: PMC9325432 DOI: 10.1002/anie.202202193] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2022] [Indexed: 12/22/2022]
Abstract
Herein, we expose how the antagonistic relationship between solid‐state luminescence and photocyclization of oligoaryl alkene chromophores is modulated by the conjugation length of their alkenyl backbones. Heptaaryl cycloheptatriene molecular rotors exhibit aggregation‐induced emission characteristics. We show that their emission is turned off upon breaking the conjugation of the cycloheptatriene by epoxide formation. While this modification is deleterious to photoluminescence, it enables formation of extended polycyclic frameworks by Mallory reactions. We exploit this dichotomy (i) to manipulate emission properties in a controlled manner and (ii) as a synthetic tool to link together pairs of phenyl rings in a specific sequence. This method to alter the tendency of oligoaryl alkenes to undergo photocyclization can inform the design of solid‐state emitters that avoid this quenching mechanism, while also allowing selective cyclization in syntheses of polycyclic aromatic hydrocarbons.
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Affiliation(s)
- Andrew T Turley
- Department of Chemistry, Durham University, Lower Mountjoy, Stockton Road, Durham, DH1 3LE, UK
| | - Promeet K Saha
- Department of Chemistry, Durham University, Lower Mountjoy, Stockton Road, Durham, DH1 3LE, UK
| | - Andrew Danos
- Department of Physics, Durham University, Lower Mountjoy, Stockton Road, Durham, DH1 3LE, UK
| | - Aisha N Bismillah
- Department of Chemistry, Durham University, Lower Mountjoy, Stockton Road, Durham, DH1 3LE, UK
| | - Andrew P Monkman
- Department of Physics, Durham University, Lower Mountjoy, Stockton Road, Durham, DH1 3LE, UK
| | - Dmitry S Yufit
- Department of Chemistry, Durham University, Lower Mountjoy, Stockton Road, Durham, DH1 3LE, UK
| | - Basile F E Curchod
- Department of Chemistry, Durham University, Lower Mountjoy, Stockton Road, Durham, DH1 3LE, UK
| | - Marc K Etherington
- Department of Physics, Durham University, Lower Mountjoy, Stockton Road, Durham, DH1 3LE, UK.,Department of Mathematics, Physics and Electrical Engineering, Northumbria University, Ellison Place, Newcastle upon Tyne, NE1 8ST, UK
| | - Paul R McGonigal
- Department of Chemistry, Durham University, Lower Mountjoy, Stockton Road, Durham, DH1 3LE, UK
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18
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Turley AT, Saha PK, Danos A, Bismillah AN, Monkman AP, Yufit DS, Curchod BFE, Etherington MK, McGonigal PR. Extended Conjugation Attenuates the Quenching of Aggregation‐Induced Emitters by Photocyclization Pathways. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202202193] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
| | | | - Andrew Danos
- Durham University Department of Physics UNITED KINGDOM
| | | | | | - Dmitry S Yufit
- Durham University Department of Chemistry UNITED KINGDOM
| | | | - Marc Kenneth Etherington
- Northumbria University Department of Mathematics, Physics, and Electrical Engineering UNITED KINGDOM
| | - Paul Ronald McGonigal
- Durham University Department of Chemistry Lower Mountjoy DH1 3LE Durham UNITED KINGDOM
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19
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Kaminski JM, Rodríguez-Serrano A, Dinkelbach F, Miranda-Salinas H, Monkman AP, Marian CM. Vibronic effects accelerate the intersystem crossing processes of the through-space charge transfer states in the triptycene bridged acridine–triazine donor–acceptor molecule TpAT-tFFO. Chem Sci 2022; 13:7057-7066. [PMID: 35774172 PMCID: PMC9200131 DOI: 10.1039/d1sc07101g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2021] [Accepted: 02/16/2022] [Indexed: 11/21/2022] Open
Abstract
Quantum chemical studies employing combined density functional and multireference configuration interaction methods suggest five excited electronic states to be involved in the prompt and delayed fluorescence emission of TpAT-tFFO. Three of them, a pair of singlet and triplet charge transfer (CT) states (S1 and T1) and a locally excited (LE) triplet state (T3), can be associated with the (Me → N) conformer, the other two CT-type states (S2 and T2) form the lowest excited singlet and triplet states of the (Me → Ph) conformer. The two conformers, which differ in essence by the shearing angle of the face-to-face aligned donor and acceptor moieties, are easily interconverted in the electronic ground state whereas the reorganization energy is substantial in the excited singlet state, thus explaining the two experimentally observed time constants of prompt fluorescence emission. Forward and reverse intersystem crossing between the singlet and triplet CT states is mediated by vibronic spin–orbit interactions involving the LE T3 state. Low-frequency vibrational modes altering the distance and alignment of the donor and acceptor π-systems tune the S1 and T3 states (likewise S2 and T3) into and out of resonance. The enhancement of intersystem crossing due to the interplay of vibronic and spin–orbit coupling is considered a general feature of organic through-space charge-transfer thermally activated delayed fluorescence emitters. DFT/MRCI quantum chemical studies suggest five excited electronic states to be involved in the prompt and delayed fluorescence emission of TpAT-tFFO.![]()
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Affiliation(s)
- Jeremy M. Kaminski
- Institute of Theoretical and Computational Chemistry, Heinrich-Heine-University Düsseldorf, D-40204 Düsseldorf, Germany
| | - Angela Rodríguez-Serrano
- Institute of Theoretical and Computational Chemistry, Heinrich-Heine-University Düsseldorf, D-40204 Düsseldorf, Germany
| | - Fabian Dinkelbach
- Institute of Theoretical and Computational Chemistry, Heinrich-Heine-University Düsseldorf, D-40204 Düsseldorf, Germany
| | | | - Andrew P. Monkman
- Dept of Physics, OEM Research Group, Durham University, Durham, DH1 3LE, UK
| | - Christel M. Marian
- Institute of Theoretical and Computational Chemistry, Heinrich-Heine-University Düsseldorf, D-40204 Düsseldorf, Germany
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20
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Farias G, Salla CAM, Aydemir M, Sturm L, Dechambenoit P, Durola F, de Souza B, Bock H, Monkman AP, Bechtold IH. Halogenation of a twisted non-polar π-system as a tool to modulate phosphorescence at room temperature. Chem Sci 2021; 12:15116-15127. [PMID: 34909153 PMCID: PMC8612374 DOI: 10.1039/d1sc04936d] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2021] [Accepted: 10/28/2021] [Indexed: 11/21/2022] Open
Abstract
Halogenation of a twisted three-fold symmetric hydrocarbon with F, Cl or Br leads to strong modulation of triplet-triplet annihilation and dual phosphorescence, one thermally activated and the other very persistent and visible by eye, with different relative contributions depending on the halide. The room temperature phosphorescence is highly unusual given the absence of lone-pair-contributing heteroatoms. The interplay between the spin-orbit coupling matrix elements and the spatial configuration of the triplet state induces efficient intersystem crossing and thus room temperature phosphorescence even without relying on heteroatomic electron lone pairs. A ninefold increase of the ISC rate after introduction of three bromine atoms is accompanied by a much higher 34-fold increase of phosphorescence rate.
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Affiliation(s)
- Giliandro Farias
- Department of Chemistry, Universidade Federal de Santa Catarina 88040-900 Florianópolis SC Brazil
| | - Cristian A M Salla
- Department of Physics, Universidade Federal de Santa Catarina 88040-900 Florianópolis SC Brazil
| | - Murat Aydemir
- Department of Physics, Durham University South Road Durham DH1 3LE UK
- Erzurum Technical University, Department of Fundamental Sciences Erzurum Turkey
| | - Ludmilla Sturm
- Centre de Recherche Paul Pascal, CNRS, Université de Bordeaux 115, av. Schweitzer 33600 Pessac France
| | - Pierre Dechambenoit
- Centre de Recherche Paul Pascal, CNRS, Université de Bordeaux 115, av. Schweitzer 33600 Pessac France
| | - Fabien Durola
- Centre de Recherche Paul Pascal, CNRS, Université de Bordeaux 115, av. Schweitzer 33600 Pessac France
| | - Bernardo de Souza
- Department of Chemistry, Universidade Federal de Santa Catarina 88040-900 Florianópolis SC Brazil
| | - Harald Bock
- Centre de Recherche Paul Pascal, CNRS, Université de Bordeaux 115, av. Schweitzer 33600 Pessac France
| | - Andrew P Monkman
- Department of Physics, Durham University South Road Durham DH1 3LE UK
| | - Ivan H Bechtold
- Department of Physics, Universidade Federal de Santa Catarina 88040-900 Florianópolis SC Brazil
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21
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Haase N, Danos A, Pflumm C, Stachelek P, Brütting W, Monkman AP. Are the rates of dexter transfer in TADF hyperfluorescence systems optically accessible? Mater Horiz 2021; 8:1805-1815. [PMID: 34846509 DOI: 10.1039/d0mh01666g] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Seemingly not, but for unexpected reasons. Combining the triplet harvesting properties of TADF materials with the fast emission rates and colour purity of fluorescent emitters is attractive for developing high performance OLEDs. In this "hyperfluorescence" approach, triplet excitons are converted to singlets on the TADF material and transferred to the fluorescent material by long range Förster energy transfer. The primary loss mechanism is assumed to be Dexter energy transfer from the TADF triplet to the non-emissive triplet of the fluorescent emitter. Here we use optical spectroscopy to investigate energy transfer in representative emissive layers. Despite observing kinetics that at first appear consistent with Dexter quenching of the TADF triplet state, transient absorption, photoluminescence quantum yields, and comparison to phosphor-sensitised "hyperphosphorescent" systems reveal that this is not the case. While Dexter quenching by the fluorescent emitter is likely still a key loss mechanism in devices, we demonstrate that - despite initial appearances - it is inoperative under optical excitation. These results reveal a deep limitation of optical spectroscopy in characterizing hyperfluorescent systems.
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Affiliation(s)
- Nils Haase
- Institute of Physics, Experimental Physics IV, University of Augsburg, Universitätsstr. 1, 86135 Augsburg, Germany
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22
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Hempe M, Kukhta NA, Danos A, Fox MA, Batsanov AS, Monkman AP, Bryce MR. Vibrational Damping Reveals Vibronic Coupling in Thermally Activated Delayed Fluorescence Materials. Chem Mater 2021; 33:3066-3080. [PMID: 34267422 PMCID: PMC8273894 DOI: 10.1021/acs.chemmater.0c03783] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2020] [Revised: 04/05/2021] [Indexed: 05/18/2023]
Abstract
We investigate a series of D-A molecules consisting of spiro[acridan-9,9'-fluorene] as the donor and 2-phenylenepyrimidine as the acceptor. In two of the materials, a spiro center effectively electronically isolates the D unit from (consequently) optically innocent yet structurally influential adamantyl side groups. In a third material, adamantyl groups attached directly to the acceptor strongly influence the electronic properties. Steady-state and time-resolved photophysical studies in solution, Zeonex polymer matrix, and neat films reveal that the substituents impact the efficiency of vibronic coupling between singlet and triplet states relevant to reverse intersystem crossing (rISC) and thermally activated delayed fluorescence (TADF), without significantly changing the singlet-triplet gap in the materials. The adamantyl groups serve to raise the segmental mass and inertia, thereby damping intramolecular motions (both vibrational and rotational). This substitution pattern reveals the role of large-amplitude (primarily D-A dihedral angle rocking) motions on reverse intersystem crossing (rISC), as well as smaller contributions from low-amplitude or dampened vibrations in solid state. We demonstrate that rISC still occurs when the high-amplitude motions are suppressed in Zeonex and discuss various vibronic coupling scenarios that point to an underappreciated role of intersegmental motions that persist in rigid solids. Our results underline the complexity of vibronic couplings in the mediation of rISC and provide a synthetic tool to enable future investigations of vibronic coupling through selective mechanical dampening with no impact on electronic systems.
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Affiliation(s)
- Matthias Hempe
- Chemistry
Department, Durham University, South Road, Durham DH1 3LE, U.K.
| | - Nadzeya A. Kukhta
- Chemistry
Department, Durham University, South Road, Durham DH1 3LE, U.K.
| | - Andrew Danos
- Physics
Department, Durham University, South Road, Durham DH1 3LE, U.K.
| | - Mark A. Fox
- Chemistry
Department, Durham University, South Road, Durham DH1 3LE, U.K.
| | - Andrei S. Batsanov
- Chemistry
Department, Durham University, South Road, Durham DH1 3LE, U.K.
| | - Andrew P. Monkman
- Physics
Department, Durham University, South Road, Durham DH1 3LE, U.K.
| | - Martin R. Bryce
- Chemistry
Department, Durham University, South Road, Durham DH1 3LE, U.K.
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23
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Wright IA, Danos A, Montanaro S, Batsanov AS, Monkman AP, Bryce MR. Conformational Dependence of Triplet Energies in Rotationally Hindered N- and S-Heterocyclic Dimers: New Design and Measurement Rules for High Triplet Energy OLED Host Materials. Chemistry 2021; 27:6545-6556. [PMID: 33560550 PMCID: PMC8251716 DOI: 10.1002/chem.202100036] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2021] [Revised: 02/08/2021] [Indexed: 12/22/2022]
Abstract
A series of four heterocyclic dimers has been synthesized, with twisted geometries imposed across the central linking bond by ortho-alkoxy chains. These include two isomeric bicarbazoles, a bis(dibenzothiophene-S,S-dioxide) and a bis(thioxanthene-S,S-dioxide). Spectroscopic and electrochemical methods, supported by density functional theory, have given detailed insights into how para- vs. meta- vs. broken conjugation, and electron-rich vs. electron-poor heterocycles impact the HOMO-LUMO gap and singlet and triplet energies. Crucially for applications as OLED hosts, the triplet energy (ET ) of these molecules was found to vary significantly between dilute polymer films and neat films, related to conformational demands of the molecules in the solid state. One of the bicarbazole species shows a variation in ET of 0.24 eV in the different media-sufficiently large to "make-or-break" an OLED device-with similar discrepancies found between neat films and frozen solution measurements of other previously reported OLED hosts. From consolidated optical and optoelectronic investigations of different host/dopant combinations, we identify that only the lower ET values measured in neat films give a reliable indicator of host/guest compatibility. This work also provides new molecular design rules for obtaining very high ET materials and controlling their HOMO and LUMO energies.
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Affiliation(s)
- Iain A. Wright
- Department of ChemistryDurham UniversitySouth RoadDurhamDH1 3LEUK
- Department of ChemistryLoughborough UniversityLoughboroughLeicestershireLE11 3TUUK
| | - Andrew Danos
- Department of PhysicsDurham UniversitySouth RoadDurhamDH1 3LEUK
| | - Stephanie Montanaro
- Department of ChemistryLoughborough UniversityLoughboroughLeicestershireLE11 3TUUK
| | | | | | - Martin R. Bryce
- Department of ChemistryDurham UniversitySouth RoadDurhamDH1 3LEUK
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24
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Kumar S, Franca LG, Stavrou K, Crovini E, Cordes DB, Slawin AMZ, Monkman AP, Zysman-Colman E. Investigation of Intramolecular Through-Space Charge-Transfer States in Donor-Acceptor Charge-Transfer Systems. J Phys Chem Lett 2021; 12:2820-2830. [PMID: 33719455 PMCID: PMC8041366 DOI: 10.1021/acs.jpclett.1c00265] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2021] [Accepted: 03/04/2021] [Indexed: 05/29/2023]
Abstract
Commonly, thermally activated delayed fluorescence (TADF) emitters present a twisted donor-acceptor structure. Here, electronic communication is mediated through-bond via π-conjugation between donor and acceptor groups. A second class of TADF emitters are those where electronic communication between donor and acceptor moieties is mediated through-space. In these through-space charge-transfer (TSCT) architectures, the donor and acceptor groups are disposed in a pseudocofacial orientation and linked via a bridging group that is typically an arene (or heteroarene). In most of these systems, there is no direct evidence that the TSCT is the dominant contributor to the communication between the donor and acceptor. Herein we investigate the interplay between through-bond localized excited (LE) and charge-transfer (CT) states and the TSCT in a rationally designed emitter, TPA-ace-TRZ, and a family of model compounds. From our photophysical studies, TSCT TADF in TPA-ace-TRZ is unambiguously confirmed and supported by theoretical modeling.
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Affiliation(s)
- Shiv Kumar
- Organic
Semiconductor Centre, EaStCHEM School of Chemistry, University of St. Andrews, St. Andrews, Fife, U.K. KY16 9ST
| | | | - Kleitos Stavrou
- Department
of Physics, Durham University, Durham, U.K. DH1 3LE
| | - Ettore Crovini
- Organic
Semiconductor Centre, EaStCHEM School of Chemistry, University of St. Andrews, St. Andrews, Fife, U.K. KY16 9ST
| | - David B. Cordes
- Organic
Semiconductor Centre, EaStCHEM School of Chemistry, University of St. Andrews, St. Andrews, Fife, U.K. KY16 9ST
| | - Alexandra M. Z. Slawin
- Organic
Semiconductor Centre, EaStCHEM School of Chemistry, University of St. Andrews, St. Andrews, Fife, U.K. KY16 9ST
| | | | - Eli Zysman-Colman
- Organic
Semiconductor Centre, EaStCHEM School of Chemistry, University of St. Andrews, St. Andrews, Fife, U.K. KY16 9ST
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25
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Stavrou K, Franca LG, Monkman AP. Photophysics of TADF Guest-Host Systems: Introducing the Idea of Hosting Potential. ACS Appl Electron Mater 2020; 2:2868-2881. [PMID: 32984822 PMCID: PMC7513578 DOI: 10.1021/acsaelm.0c00514] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2020] [Accepted: 08/11/2020] [Indexed: 05/29/2023]
Abstract
The thermally activated delayed fluorescence (TADF) donor-acceptor (D-A) molecule, DMAC-TRZ, is used as a TADF emitter "probe" to distinguish the environmental effects of a range of solid-state host materials in guest-host systems. Using the guest's photophysical behavior in solution as a benchmark, a comprehensive study using a variety of typical TADF organic light-emitting diode hosts with different characteristics provides a clearer understanding of guest-host interactions and what affects emitter performance in solid state. We investigate which are the key host characteristics that directly affect charge-transfer (CT) state energy and singlet triplet energy gaps. Using time-resolved photoluminescence measurements, we use the CT state energy distribution obtained from the full width at half-maximum (fwhm) of the emission band and correlate this with other photophysical properties such as the apparent dynamic red shift of CT emission on-set to estimate the disorder-induced heterogeneity of D-A dihedral angles and singlet triplet gaps. Further, the delayed emission stabilization energy value and time-dependent CT band fwhm are shown to be related to a combination of host's rigidity, emitter molecule packing, and the energy difference between guest and host lowest energy triplet states. Concentration dependence studies show that emitter dimerization/aggregation can improve as well as reduce emission efficiency depending on the characteristics of the host. Two similar host materials, mCPCN and mCBPCN, with optimum host characteristics show completely different behaviors, and their hosting potential is extensively explored. We demonstrate that type I and type III TADF emitters behave differently in the same host and that the materials with intrinsic small ΔE ST have the smallest disorder-induced CT energy and reverse intersystem crossing rate dispersion. We also present an optimized method to define the actual triplet energy of a guest-host system, a crucial parameter in understanding the overall mechanism of the TADF efficiency of the system.
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26
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Turley AT, Danos A, Prlj A, Monkman AP, Curchod BFE, McGonigal PR, Etherington MK. Modulation of charge transfer by N-alkylation to control photoluminescence energy and quantum yield. Chem Sci 2020; 11:6990-6995. [PMID: 34122995 PMCID: PMC8159361 DOI: 10.1039/d0sc02460k] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Charge transfer in organic fluorophores is a fundamental photophysical process that can be either beneficial, e.g., facilitating thermally activated delayed fluorescence, or detrimental, e.g., mediating emission quenching. N-Alkylation is shown to provide straightforward synthetic control of the charge transfer, emission energy and quantum yield of amine chromophores. We demonstrate this concept using quinine as a model. N-Alkylation causes changes in its emission that mirror those caused by changes in pH (i.e., protonation). Unlike protonation, however, alkylation of quinine's two N sites is performed in a stepwise manner to give kinetically stable species. This kinetic stability allows us to isolate and characterize an N-alkylated analogue of an ‘unnatural’ protonation state that is quaternized selectively at the less basic site, which is inaccessible using acid. These materials expose (i) the through-space charge-transfer excited state of quinine and (ii) the associated loss pathway, while (iii) developing a simple salt that outperforms quinine sulfate as a quantum yield standard. This N-alkylation approach can be applied broadly in the discovery of emissive materials by tuning charge-transfer states. A versatile N-alkylation strategy controls the presence of charge-transfer excited states and the emission colour of N-heterocyclic chromophores.![]()
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Affiliation(s)
- Andrew T Turley
- Department of Chemistry, Durham University South Road Durham DH1 3LE UK
| | - Andrew Danos
- Department of Physics, Durham University South Road Durham DH1 3LE UK
| | - Antonio Prlj
- Department of Chemistry, Durham University South Road Durham DH1 3LE UK
| | - Andrew P Monkman
- Department of Physics, Durham University South Road Durham DH1 3LE UK
| | | | - Paul R McGonigal
- Department of Chemistry, Durham University South Road Durham DH1 3LE UK
| | - Marc K Etherington
- Department of Physics, Durham University South Road Durham DH1 3LE UK .,Department of Mathematics, Physics and Electrical Engineering, Northumbria University Ellison Place NE1 8ST UK
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27
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Scholz R, Kleine P, Lygaitis R, Popp L, Lenk S, Etherington MK, Monkman AP, Reineke S. Investigation of Thermally Activated Delayed Fluorescence from a Donor-Acceptor Compound with Time-Resolved Fluorescence and Density Functional Theory Applying an Optimally Tuned Range-Separated Hybrid Functional. J Phys Chem A 2020; 124:1535-1553. [PMID: 32024366 DOI: 10.1021/acs.jpca.9b11083] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Emitters showing thermally activated delayed fluorescence (TADF) in electroluminescent devices rely on efficient reverse intersystem crossing (rISC) arising from small thermal activation barriers between the lowest excited triplet and singlet manifolds. A small donor-acceptor compound consisting of a demethylacridine donor and a methylbenzoate acceptor group is used as a model TADF emitter. The spectroscopic signatures of this system are characterized using a combination of photoluminescence and photoluminescence excitation, and the photoluminescence decay dynamics are recorded between delays of 2 ns and 20 ms. Above T = 200 K, our data provide convincing evidence for TADF at intermediate delays in the microsecond range, whereas triplet-triplet annihilation and slow triplet decay at later times can be observed over the entire temperature range from T = 80 K to room temperature. Moreover, close to room temperature, we find a second and faster up-conversion mechanism, tentatively assigned to reverse internal conversion between different triplet configurations. An interpretation of these experimental findings requires a calculation of the deformation patterns and potential minima of several electronic configurations. This task is performed with a range-separated hybrid functional, outperforming standard density functionals or global hybrids. In particular, the systematic underestimation of the energy of charge transfer (CT) states with respect to local excitations within the constituting chromophores is replaced by more reliable transition energies for both kinds of excitations. Hence, several absorption and emission features can be assigned unambiguously, and the observed activation barriers for rISC and reverse internal conversion correspond to calculated energy differences between the potential surfaces in different electronic configurations.
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Affiliation(s)
- Reinhard Scholz
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics , Technische Universität Dresden , 01062 Dresden , Germany.,Leibniz Institute of Polymer Research Dresden , P.O. Box 120 411, 01005 Dresden , Germany
| | - Paul Kleine
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics , Technische Universität Dresden , 01062 Dresden , Germany
| | - Ramunas Lygaitis
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics , Technische Universität Dresden , 01062 Dresden , Germany.,Department of Organic Technology , Kaunas University of Technology , Radvilenu Plentas 19 , LT 3028 Kaunas , Lithuania
| | - Ludwig Popp
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics , Technische Universität Dresden , 01062 Dresden , Germany
| | - Simone Lenk
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics , Technische Universität Dresden , 01062 Dresden , Germany
| | - Marc K Etherington
- Organic Electroactive Materials Research Group, Physics Department , Durham University , South Road , Durham DH1 3LE , United Kingdom.,Department of Mathematics, Physics & Electrical Engineering , Northumbria University , Ellison Place , Newcastle upon Tyne NE1 8ST , United Kingdom
| | - Andrew P Monkman
- Organic Electroactive Materials Research Group, Physics Department , Durham University , South Road , Durham DH1 3LE , United Kingdom
| | - Sebastian Reineke
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics , Technische Universität Dresden , 01062 Dresden , Germany
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28
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Benjamin H, Zheng Y, Kozhevnikov VN, Siddle JS, O'Driscoll LJ, Fox MA, Batsanov AS, Griffiths GC, Dias FB, Monkman AP, Bryce MR. Unusual dual-emissive heteroleptic iridium complexes incorporating TADF cyclometalating ligands. Dalton Trans 2020; 49:2190-2208. [DOI: 10.1039/c9dt04672k] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Five new neutral heteroleptic iridium(iii) complexes IrL2(pic) (2–6) based on the archetypical blue emitter FIrpic have been synthesised.
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Affiliation(s)
- Helen Benjamin
- Department of Chemistry
- Durham University
- Durham DH1 3LE
- UK
| | - Yonghao Zheng
- Department of Chemistry
- Durham University
- Durham DH1 3LE
- UK
- School of Optoelectronic Science and Engineering
| | - Valery N. Kozhevnikov
- Department of Chemistry
- Durham University
- Durham DH1 3LE
- UK
- Department of Applied Sciences
| | | | | | - Mark A. Fox
- Department of Chemistry
- Durham University
- Durham DH1 3LE
- UK
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29
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Ward J, Kukhta NA, dos Santos PL, Congrave DG, Batsanov AS, Monkman AP, Bryce MR. Delayed Blue Fluorescence via Upper-Triplet State Crossing from C-C Bonded Donor-Acceptor Charge Transfer Molecules with Azatriangulene Cores. Chem Mater 2019; 31:6684-6695. [PMID: 32063676 PMCID: PMC7011764 DOI: 10.1021/acs.chemmater.9b01184] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2019] [Revised: 05/09/2019] [Indexed: 05/24/2023]
Abstract
We report the synthesis and structural and photophysical characterization of two series of molecules with functionalized azatriangulene electron donor cores and three pendant electron acceptor units. The presented donor and acceptor units are joined by C-C bonds, instead of the usual C-heteroatom bonds often found in thermally activated delayed fluorescence (TADF) emitters. The effects of the donor-acceptor strength and donor-acceptor dihedral angle on the emission properties are assessed. The data establish that the singlet-triplet energy gap is >0.3 eV and that delayed emission is present in only specific host matrices, irrespective of host polarity. Specific host behavior is atypical of many TADF materials, and we suggest the delayed emission in this work does not occur by a conventional vibronically coupled TADF mechanism, as the ΔE ST value is too large. Detailed photophysical analysis and supporting density functional theory calculations suggest that some presented azatriangulene molecules emit via an upper-triplet state crossing mechanism. This work highlights that several different mechanisms can be responsible for delayed emission, often with highly similar photophysics. Detailed photophysical analysis is required to establish which delayed emission mechanism is occurring. Our results also highlight a clear future direction toward vibronically coupled C-C bonded TADF materials.
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Affiliation(s)
- Jonathan
S. Ward
- Department
of Chemistry, Durham University, Durham DH1 3LE, U.K.
| | | | | | | | | | | | - Martin R. Bryce
- Department
of Chemistry, Durham University, Durham DH1 3LE, U.K.
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30
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Stachelek P, Ward JS, dos Santos PL, Danos A, Colella M, Haase N, Raynes SJ, Batsanov AS, Bryce MR, Monkman AP. Molecular Design Strategies for Color Tuning of Blue TADF Emitters. ACS Appl Mater Interfaces 2019; 11:27125-27133. [PMID: 31314484 PMCID: PMC7006999 DOI: 10.1021/acsami.9b06364] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2019] [Accepted: 07/01/2019] [Indexed: 05/24/2023]
Abstract
New thermally activated delayed fluorescence (TADF) blue emitter molecules based on the known donor-acceptor-donor (D-A-D)-type TADF molecule, 2,7-bis(9,9-dimethylacridin-10-yl)-9,9-dimethylthioxanthene-S,S-dioxide (DDMA-TXO2), are reported. The motivation for the present investigation is via the use of rational molecular design, based on DDMA-TXO2, to elevate the organic light emitting diode (OLED) performance and obtain deeper blue color coordinates. To achieve this goal, the strength of the donor (D) unit and acceptor (A) units have been tuned with methyl substituents. The methyl functionality on the acceptor was also expected to modulate the D-A torsion angle in order to obtain a blue shift in the electroluminescence. The effect of regioisomeric structures has also been investigated. Herein, we report the photophysical, electrochemical, and single-crystal X-ray crystallography data to assist with the successful OLED design. The methyl substituents on the DDMA-TXO2 framework have profound effects on the photophysics and color coordinates of the emitters. The weak electron-donating methyl groups alter the redox properties of the D and A units and consequently affect the singlet and triplet levels but not the energy gap (ΔEST). By systematically manipulating all of the aforementioned factors, devices have been obtained with acceptor-substituted III with a maximum external quantum efficiency of 22.6% and Commission Internationale de l'Éclairage coordinates of (0.15, 0.18) at 1000 cd m-2.
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Affiliation(s)
- Patrycja Stachelek
- Department
of Physics and Department of Chemistry, Durham University, Durham DH1 3LE, U.K.
| | - Jonathan S. Ward
- Department
of Physics and Department of Chemistry, Durham University, Durham DH1 3LE, U.K.
| | - Paloma L. dos Santos
- Department
of Physics and Department of Chemistry, Durham University, Durham DH1 3LE, U.K.
| | - Andrew Danos
- Department
of Physics and Department of Chemistry, Durham University, Durham DH1 3LE, U.K.
| | - Marco Colella
- Department
of Physics and Department of Chemistry, Durham University, Durham DH1 3LE, U.K.
| | - Nils Haase
- Institute
of Physics, Experimental Physics IV, University
of Augsburg, Universitätsstr.
1, Augsburg 86135, Germany
- Merck
KGaA, Performance Materials—Display Solutions, Frankfurter Straße 250, Darmstadt 64293, Germany
| | - Samuel J. Raynes
- Department
of Physics and Department of Chemistry, Durham University, Durham DH1 3LE, U.K.
| | - Andrei S. Batsanov
- Department
of Physics and Department of Chemistry, Durham University, Durham DH1 3LE, U.K.
| | - Martin R. Bryce
- Department
of Physics and Department of Chemistry, Durham University, Durham DH1 3LE, U.K.
| | - Andrew P. Monkman
- Department
of Physics and Department of Chemistry, Durham University, Durham DH1 3LE, U.K.
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31
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de Sa Pereira D, Menelaou C, Danos A, Marian C, Monkman AP. Electroabsorption Spectroscopy as a Tool for Probing Charge Transfer and State Mixing in Thermally Activated Delayed Fluorescence Emitters. J Phys Chem Lett 2019; 10:3205-3211. [PMID: 31117683 PMCID: PMC7007248 DOI: 10.1021/acs.jpclett.9b00999] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2019] [Accepted: 05/21/2019] [Indexed: 05/24/2023]
Abstract
Solid-state electroabsorption is demonstrated as a powerful tool for probing the charge transfer (CT) character and state mixing in the low-energy optical transitions of two structurally similar thermally activated delayed fluorescent (TADF) materials with divergent photophysical and device performances. The Liptay model is used to fit differentials of the low-energy absorption bands to the measured electroabsorption spectra, with both emitters showing CT characteristics and large changes in dipole moments upon excitation despite the associated absorption bands appearing to be structured. High electric fields then reveal transfer of oscillator strength to a state close to the CT in the better performing molecule. With supporting TDDFT-TDA and DFT/MRCI calculations, this state showed ππ* characteristics of a local acceptor triplet that strongly mixes with the σπ* of the CT. The emitter with poor TADF performance showed no evidence of such mixing.
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Affiliation(s)
- Daniel de Sa Pereira
- Department
of Physics, Durham University, South Road, Durham DH1 3LE, United
Kingdom
| | - Christopher Menelaou
- Department
of Physics, Durham University, South Road, Durham DH1 3LE, United
Kingdom
| | - Andrew Danos
- Department
of Physics, Durham University, South Road, Durham DH1 3LE, United
Kingdom
| | - Christel Marian
- Institut
für Theoretische Chemie, Heinrich-Heine-Universität, Universitätsstrasse 1, 40225 Düsseldorf, Germany
| | - Andrew P. Monkman
- Department
of Physics, Durham University, South Road, Durham DH1 3LE, United
Kingdom
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32
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Woon KL, Yi CL, Pan KC, Etherington MK, Wu CC, Wong KT, Monkman AP. Intramolecular Dimerization Quenching of Delayed Emission in Asymmetric D-D'-A TADF Emitters. J Phys Chem C Nanomater Interfaces 2019; 123:12400-12410. [PMID: 32952765 PMCID: PMC7493288 DOI: 10.1021/acs.jpcc.9b01900] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2019] [Revised: 04/17/2019] [Indexed: 05/29/2023]
Abstract
Understanding the excited-state dynamics and conformational relaxation in thermally activated delayed fluorescence (TADF) molecules, including conformations that potentially support intramolecular through-space charge transfer, can open new avenues for TADF molecular design as well as elucidate complex photophysical pathways in structurally complex molecules. Emissive molecules comprising a donor (triphenylamine, TPA) and an acceptor (triphenyltriazine, TRZ) bridged by a second donor (9,9-dimethyl-9-10-dihydroacridin, DMAC, or phenoxazine, PXZ) are synthesized and characterized. In solution, the flexibility of the sp3-hybridized carbon atom in DMAC of DMAC-TPA-TRZ, compared to the rigid PXZ, allows significant conformational reorganization, giving rise to multiple charge-transfer excited states. As a result of such a reorganization, the TRZ and TPA moieties become cofacially aligned, driven by a strong dipole-dipole attraction between the TPA and TRZ units, forming a weakly charge-transfer dimer state, in stark contrast to the case of PXZ-TPA-TRZ where the rigid PXZ bridge only supports a single PXZ-TRZ charge transfer (CT) state. The low-energy TPA-TRZ dimer is found to have a high-energy dimer local triplet state, which quenches delayed emission because the resultant singlet CT local triplet energy gap is too large to mediate efficient reverse intersystem crossing. However, organic light-emitting diodes using PXZ-TPA-TRZ as an emitting dopant resulted in external quantum efficiency as high as 22%, more than two times higher than that of DMAC-TPA-TRZ-based device, showing the impact that such intramolecular reorganization and donor-acceptor dimerization have on TADF performance.
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Affiliation(s)
- Kai-Lin Woon
- Department
of Physics, Durham University, South Road, Durham DH1 3LE, U.K.
- Low
Dimensional Materials Research Centre, Department of Physics, University of Malaya, Kuala Lumpur 50603, Malaysia
| | - Chih-Lun Yi
- Department
of Chemistry, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan
| | - Kuan-Chung Pan
- Department
of Electrical Engineering, Graduate Institute of Electronics Engineering,
and Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei 10617, Taiwan
| | | | - Chung-Chih Wu
- Department
of Electrical Engineering, Graduate Institute of Electronics Engineering,
and Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei 10617, Taiwan
| | - Ken-Tsung Wong
- Department
of Chemistry, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan
- Institute
of Atomic and Molecular Science, Academia
Sinica, Taipei 10617, Taiwan
| | - Andrew P. Monkman
- Department
of Physics, Durham University, South Road, Durham DH1 3LE, U.K.
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33
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Etherington MK, Kukhta NA, Higginbotham HF, Danos A, Bismillah AN, Graves DR, McGonigal PR, Haase N, Morherr A, Batsanov AS, Pflumm C, Bhalla V, Bryce MR, Monkman AP. Persistent Dimer Emission in Thermally Activated Delayed Fluorescence Materials. J Phys Chem C Nanomater Interfaces 2019; 123:11109-11117. [PMID: 31080540 PMCID: PMC6501699 DOI: 10.1021/acs.jpcc.9b01458] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2019] [Indexed: 05/22/2023]
Abstract
We expose significant changes in the emission color of carbazole-based thermally activated delayed fluorescence (TADF) emitters that arise from the presence of persistent dimer states in thin films and organic light-emitting diodes (OLEDs). Direct photoexcitation of this dimer state in 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) reveals the significant influence of dimer species on the color purity of its photoluminescence and electroluminescence. The dimer species is sensitive to the sample preparation method, and its enduring presence contributes to the widely reported concentration-mediated red shift in the photoluminescence and electroluminescence of evaporated thin films. This discovery has implications on the usability of these, and similar, molecules for OLEDs and explains disparate electroluminescence spectra presented in the literature for these compounds. The dimerization-controlled changes observed in the TADF process and photoluminescence efficiency mean that careful consideration of dimer states is imperative in the design of future TADF emitters and the interpretation of previously reported studies of carbazole-based TADF materials.
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Affiliation(s)
- Marc K. Etherington
- Department
of Physics and Department of Chemistry, Durham University, South Road, Durham DH1
3LE, U.K.
- E-mail:
| | - Nadzeya A. Kukhta
- Department
of Physics and Department of Chemistry, Durham University, South Road, Durham DH1
3LE, U.K.
| | - Heather F. Higginbotham
- Department
of Physics and Department of Chemistry, Durham University, South Road, Durham DH1
3LE, U.K.
| | - Andrew Danos
- Department
of Physics and Department of Chemistry, Durham University, South Road, Durham DH1
3LE, U.K.
| | - Aisha N. Bismillah
- Department
of Physics and Department of Chemistry, Durham University, South Road, Durham DH1
3LE, U.K.
| | - David R. Graves
- Department
of Physics and Department of Chemistry, Durham University, South Road, Durham DH1
3LE, U.K.
| | - Paul R. McGonigal
- Department
of Physics and Department of Chemistry, Durham University, South Road, Durham DH1
3LE, U.K.
| | - Nils Haase
- Merck
KGaA, Performance Materials—Display Solutions, Frankfurter Straße 250, 64293 Darmstadt, Germany
- Institute
of Physics, Experimental Physics IV, University
of Augsburg, Universitätsstr.
1, 86135 Augsburg, Germany
| | - Antonia Morherr
- Merck
KGaA, Performance Materials—Display Solutions, Frankfurter Straße 250, 64293 Darmstadt, Germany
| | - Andrei S. Batsanov
- Department
of Physics and Department of Chemistry, Durham University, South Road, Durham DH1
3LE, U.K.
| | - Christof Pflumm
- Merck
KGaA, Performance Materials—Display Solutions, Frankfurter Straße 250, 64293 Darmstadt, Germany
| | - Vandana Bhalla
- Department
of Physics and Department of Chemistry, Durham University, South Road, Durham DH1
3LE, U.K.
- Department
of Chemistry, Guru Nanak Dev University, Grand Trunk Road, Off NH 1, Amritsar, Punjab 143005, India
| | - Martin R. Bryce
- Department
of Physics and Department of Chemistry, Durham University, South Road, Durham DH1
3LE, U.K.
| | - Andrew P. Monkman
- Department
of Physics and Department of Chemistry, Durham University, South Road, Durham DH1
3LE, U.K.
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34
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Colella M, Danos A, Monkman AP. Less Is More: Dilution Enhances Optical and Electrical Performance of a TADF Exciplex. J Phys Chem Lett 2019; 10:793-798. [PMID: 30726086 PMCID: PMC7005938 DOI: 10.1021/acs.jpclett.8b03646] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2018] [Accepted: 02/06/2019] [Indexed: 05/25/2023]
Abstract
A surprising yet highly practical approach to improve the performance of a TADF exciplex blend is reported. Using the TSBPA donor and PO-T2T acceptor to form an exciplex, we are able to blue shift the emission, increase PLQY from 58 to 80%, and increase the device EQE from 14.8 to 19.2% by simply diluting the exciplex with an inert high triplet energy host material-here either UGH-3 or DPEPO. These effects are explained in terms of an increasing donor-acceptor distance and associated charge separation, while different behaviors observed in the different hosts are attributed to different energy barriers to electron transfer through the host. We expect that the observed performance-enhancing effects of dilution will be general to different exciplex blends and host materials and offer a new way to optimize the electrical properties of exciplex emission layers with narrow blue emission.
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35
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Dos Santos PL, Silveira OJ, Huang R, Jardim GAM, Matos MJS, da Silva Júnior EN, Monkman AP, Dias FB, Cury LA. Dynamics of aggregated states resolved by gated fluorescence in films of room temperature phosphorescent emitters. Phys Chem Chem Phys 2019; 21:3814-3821. [PMID: 30698176 DOI: 10.1039/c8cp07005a] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Phenazine derivative molecules were studied using steady state and time resolved fluorescence techniques and demonstrated to lead to strong formation of aggregated species, identified as dimers by time dependent density functional theory calculations. Blended films in a matrix of Zeonex®, produced at different concentrations, showed different contributions of dimer and monomer emissions in a prompt time frame, e.g. less than 50 ns. In contrast, the phosphorescence (e.g. emission from the triplet state) shows no significant effect on dimer formation, although strong dependence of the phosphorescence intensity on concentration is observed, leading to phosphorescence being quenched at higher concentration.
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Affiliation(s)
- Paloma L Dos Santos
- Department of Physics, University of Durham, South Road DH1 3LE, Durham, UK.
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36
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Colella M, Pander P, Pereira DDS, Monkman AP. Interfacial TADF Exciplex as a Tool to Localize Excitons, Improve Efficiency, and Increase OLED Lifetime. ACS Appl Mater Interfaces 2018; 10:40001-40007. [PMID: 30381946 DOI: 10.1021/acsami.8b15942] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
In this work, we employ a thermally activated delayed fluorescence (TADF) exciplex formed between the emissive layer (EML) host, 26DCzPPy, and the electron transport layer (ETL) 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine at the interface between the EML and the ETL to improve the stability and efficiency of a phosphorescence organic light-emitting diode based on Ir(dmpq)2acac. We show that the presence of the TADF exciplex at the EML-ETL interface induces an efficient localization of the recombination zone, which is confined within the 5 nm thick EML. Furthermore, the TADF exciplex allows harvesting of the holes and electrons that piled up at the EML-ETL interface and transfers the resultant excited state energy to the phosphorescent emitter through Förster and/or Dexter energy transfer. This approach effectively improves the LT90 of devices from <1 min to 6 h by limiting recombination processes outside of the 5 nm EML.
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Affiliation(s)
- Marco Colella
- Physics Department , Durham University , South Road , Durham DH1 3LE , United Kingdom
| | - Piotr Pander
- Physics Department , Durham University , South Road , Durham DH1 3LE , United Kingdom
| | - Daniel de Sa Pereira
- Physics Department , Durham University , South Road , Durham DH1 3LE , United Kingdom
| | - Andrew P Monkman
- Physics Department , Durham University , South Road , Durham DH1 3LE , United Kingdom
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Abstract
A method for producing simple and efficient thermally-activated delayed fluorescence organic light-emitting diodes (OLEDs) based on guest-host or exciplex donor-acceptor emitters is presented. With a step-by-step procedure, readers will be able to repeat and produce OLED devices based on simple organic emitters. A patterning procedure allowing the creation of personalized indium tin oxide (ITO) shape is shown. This is followed by the evaporation of all layers, encapsulation and characterization of each individual device. The end goal is to present a procedure that will give the opportunity to repeat the information presented in cited publication but also using different compounds and structures in order to prepare efficient OLEDs.
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Affiliation(s)
| | | | - Przemyslaw Data
- Physics Department, Durham University; Faculty of Chemistry, Silesian University of Technology; Centre of Polymer and Carbon Materials, Polish Academy of Science;
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38
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Oh CS, Pereira DDS, Han SH, Park HJ, Higginbotham HF, Monkman AP, Lee JY. Dihedral Angle Control of Blue Thermally Activated Delayed Fluorescent Emitters through Donor Substitution Position for Efficient Reverse Intersystem Crossing. ACS Appl Mater Interfaces 2018; 10:35420-35429. [PMID: 30238749 DOI: 10.1021/acsami.8b10595] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
This study shows a molecular design strategy for controlling the dihedral angle of two carbazole donors linked to a 2,4-diphenyl-1,3,5-triazine acceptor by a phenyl unit. Using this approach, six thermally activated delayed fluorescence emitters were synthesized with donors placed in various positions around a central phenyl core, and the photophysical relationship between the donor position and its dihedral angle was investigated. We demonstrate that this angle can affect both the strength of the charge transfer state and the conjugation across the entire molecule, effectively changing the singlet-triplet energy gap of the system. We conclude that materials containing two substituted -ortho donors or one -ortho and an adjacent -meta have the smallest energy gaps and the shortest delayed fluorescence lifetimes. On the other hand, emitters with no -ortho substituted donors have larger energy gaps and slow-to-negligible delayed fluorescence. When applying these materials to organic light-emitting diodes, these blue-emitting devices have a range of electrical properties, the best producing efficiencies as high as 21.8% together with high resistance to roll-off that correlate with the reverse intersystem crossing rates obtained.
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Affiliation(s)
- Chan Seok Oh
- School of Chemical Engineering , Sungkyunkwan University , 2066, Seobu-ro , Jangan-gu, Suwon , Gyeonggi 440-746 , Korea
| | | | - Si Hyun Han
- School of Chemical Engineering , Sungkyunkwan University , 2066, Seobu-ro , Jangan-gu, Suwon , Gyeonggi 440-746 , Korea
| | - Hee-Jun Park
- School of Chemical Engineering , Sungkyunkwan University , 2066, Seobu-ro , Jangan-gu, Suwon , Gyeonggi 440-746 , Korea
| | | | - Andrew P Monkman
- Department of Physics , Durham University , South Road , Durham DH1 3LE , U.K
| | - Jun Yeob Lee
- School of Chemical Engineering , Sungkyunkwan University , 2066, Seobu-ro , Jangan-gu, Suwon , Gyeonggi 440-746 , Korea
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dos Santos PL, Ward JS, Congrave DG, Batsanov AS, Eng J, Stacey JE, Penfold TJ, Monkman AP, Bryce MR. Triazatruxene: A Rigid Central Donor Unit for a D-A 3 Thermally Activated Delayed Fluorescence Material Exhibiting Sub-Microsecond Reverse Intersystem Crossing and Unity Quantum Yield via Multiple Singlet-Triplet State Pairs. Adv Sci (Weinh) 2018; 5:1700989. [PMID: 29938177 PMCID: PMC6010696 DOI: 10.1002/advs.201700989] [Citation(s) in RCA: 77] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2017] [Revised: 02/08/2018] [Indexed: 05/23/2023]
Abstract
By inverting the common structural motif of thermally activated delayed fluorescence materials to a rigid donor core and multiple peripheral acceptors, reverse intersystem crossing (rISC) rates are demonstrated in an organic material that enables utilization of triplet excited states at faster rates than Ir-based phosphorescent materials. A combination of the inverted structure and multiple donor-acceptor interactions yields up to 30 vibronically coupled singlet and triplet states within 0.2 eV that are involved in rISC. This gives a significant enhancement to the rISC rate, leading to delayed fluorescence decay times as low as 103.9 ns. This new material also has an emission quantum yield ≈1 and a very small singlet-triplet gap. This work shows that it is possible to achieve both high photoluminescence quantum yield and fast rISC in the same molecule. Green organic light-emitting diode devices with external quantum efficiency >30% are demonstrated at 76 cd m-2.
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Affiliation(s)
| | - Jonathan S. Ward
- Department of ChemistryDurham UniversitySouth RoadDurhamDH1 3LEUK
| | | | | | - Julien Eng
- Chemistry School of Natural and Environmental SciencesNewcastle UniversityNewcastle upon TyneNE1 7RUUK
| | - Jessica E. Stacey
- Chemistry School of Natural and Environmental SciencesNewcastle UniversityNewcastle upon TyneNE1 7RUUK
| | - Thomas J. Penfold
- Chemistry School of Natural and Environmental SciencesNewcastle UniversityNewcastle upon TyneNE1 7RUUK
| | | | - Martin R. Bryce
- Department of ChemistryDurham UniversitySouth RoadDurhamDH1 3LEUK
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40
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Wright IA, Al-Attar HA, Batsanov AS, Monkman AP, Bryce MR. Conformationally-restricted bicarbazoles with phenylene bridges displaying deep-blue emission and high triplet energies: systematic structure–property relationships. Phys Chem Chem Phys 2018; 20:11867-11875. [PMID: 29662993 DOI: 10.1039/c8cp01636d] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Twelve bicarbazole derivatives with emission ranging from blue-green to deep-blue, and ET 2.6–3.0 eV.
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Affiliation(s)
- Iain A. Wright
- Department of Chemistry, Durham University
- Durham
- UK
- Department of Chemistry, Loughborough University
- Loughborough
| | - Hameed A. Al-Attar
- Department of Physics, Durham University
- Durham
- UK
- Department of Physics, Basrah University
- Basrah
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41
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Kukhta NA, Matulaitis T, Volyniuk D, Ivaniuk K, Turyk P, Stakhira P, Grazulevicius JV, Monkman AP. Deep-Blue High-Efficiency TTA OLED Using Para- and Meta-Conjugated Cyanotriphenylbenzene and Carbazole Derivatives as Emitter and Host. J Phys Chem Lett 2017; 8:6199-6205. [PMID: 29227664 DOI: 10.1021/acs.jpclett.7b02867] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Elaboration of the appropriate host materials proved to be not less important for the fabrication of a highly efficient OLED than the design of emitters. In the present work, we show how by simple variation of molecular structure both blue emitters exhibiting delayed fluorescence and ambipolar high triplet energy hosts can be obtained. The compounds with a para-junction revealed higher thermal stability (TID up to 480 °C), lower ionization potentials (5.51-5.60 eV), exclusively hole transport, and higher photoluminescence quantum efficiencies (0.90-0.97). Meta-linkage leads to ambipolar charge transport and higher triplet energies (2.82 eV). Introduction of the accepting nitrile groups in the para-position induces intensive delayed fluorescence via a triplet-triplet annihilation up-conversion mechanism. By utilization of the para-substituted derivative as an emitter and the meta-substituted isomer as the host, a deep-blue OLED with the external quantum efficiency of 14.1% was fabricated.
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Affiliation(s)
- Nadzeya A Kukhta
- Department of Polymer Chemistry and Technology, Kaunas University of Technology , Radvilenu pl. 19, LT-254 Kaunas, Lithuania
| | - Tomas Matulaitis
- Department of Polymer Chemistry and Technology, Kaunas University of Technology , Radvilenu pl. 19, LT-254 Kaunas, Lithuania
| | - Dmytro Volyniuk
- Department of Polymer Chemistry and Technology, Kaunas University of Technology , Radvilenu pl. 19, LT-254 Kaunas, Lithuania
| | - Khrystyna Ivaniuk
- Lviv Polytechnic National University , S. Bandera 12, 79013 Lviv, Ukraine
| | - Pavlo Turyk
- Lviv Polytechnic National University , S. Bandera 12, 79013 Lviv, Ukraine
| | - Pavlo Stakhira
- Lviv Polytechnic National University , S. Bandera 12, 79013 Lviv, Ukraine
| | - Juozas V Grazulevicius
- Department of Polymer Chemistry and Technology, Kaunas University of Technology , Radvilenu pl. 19, LT-254 Kaunas, Lithuania
| | - Andrew P Monkman
- Department of Physics, Durham University , South Road, Durham DH1 3LE, United Kingdom
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42
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Sturala J, Etherington MK, Bismillah AN, Higginbotham HF, Trewby W, Aguilar JA, Bromley EHC, Avestro AJ, Monkman AP, McGonigal PR. Excited-State Aromatic Interactions in the Aggregation-Induced Emission of Molecular Rotors. J Am Chem Soc 2017; 139:17882-17889. [PMID: 29151342 DOI: 10.1021/jacs.7b08570] [Citation(s) in RCA: 106] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Small, apolar aromatic groups, such as phenyl rings, are commonly included in the structures of fluorophores to impart hindered intramolecular rotations, leading to desirable solid-state luminescence properties. However, they are not normally considered to take part in through-space interactions that influence the fluorescent output. Here, we report on the photoluminescence properties of a series of phenyl-ring molecular rotors bearing three, five, six, and seven phenyl groups. The fluorescent emissions from two of the rotors are found to originate, not from the localized excited state as one might expect, but from unanticipated through-space aromatic-dimer states. We demonstrate that these relaxed dimer states can form as a result of intra- or intermolecular interactions across a range of environments in solution and solid samples, including conditions that promote aggregation-induced emission. Computational modeling also suggests that the formation of aromatic-dimer excited states may account for the photophysical properties of a previously reported luminogen. These results imply, therefore, that this is a general phenomenon that should be taken into account when designing and interpreting the fluorescent outputs of luminescent probes and optoelectronic devices based on fluorescent molecular rotors.
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Affiliation(s)
- Jiri Sturala
- Department of Chemistry and ‡Department of Physics, Durham University , Lower Mountjoy, Stockton Road, Durham DH1 3LE, United Kingdom
| | - Marc K Etherington
- Department of Chemistry and ‡Department of Physics, Durham University , Lower Mountjoy, Stockton Road, Durham DH1 3LE, United Kingdom
| | - Aisha N Bismillah
- Department of Chemistry and ‡Department of Physics, Durham University , Lower Mountjoy, Stockton Road, Durham DH1 3LE, United Kingdom
| | - Heather F Higginbotham
- Department of Chemistry and ‡Department of Physics, Durham University , Lower Mountjoy, Stockton Road, Durham DH1 3LE, United Kingdom
| | - William Trewby
- Department of Chemistry and ‡Department of Physics, Durham University , Lower Mountjoy, Stockton Road, Durham DH1 3LE, United Kingdom
| | - Juan A Aguilar
- Department of Chemistry and ‡Department of Physics, Durham University , Lower Mountjoy, Stockton Road, Durham DH1 3LE, United Kingdom
| | - Elizabeth H C Bromley
- Department of Chemistry and ‡Department of Physics, Durham University , Lower Mountjoy, Stockton Road, Durham DH1 3LE, United Kingdom
| | - Alyssa-Jennifer Avestro
- Department of Chemistry and ‡Department of Physics, Durham University , Lower Mountjoy, Stockton Road, Durham DH1 3LE, United Kingdom
| | - Andrew P Monkman
- Department of Chemistry and ‡Department of Physics, Durham University , Lower Mountjoy, Stockton Road, Durham DH1 3LE, United Kingdom
| | - Paul R McGonigal
- Department of Chemistry and ‡Department of Physics, Durham University , Lower Mountjoy, Stockton Road, Durham DH1 3LE, United Kingdom
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43
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Altınölçek N, Aydemir M, Tavaslı M, Dos Santos PL, Monkman AP. Synthesis of biscyclometalated iridium(III) acetylacetonate complexes via a 15 min bridge-splitting reaction, their characterisations and photophysical properties. J Organomet Chem 2017. [DOI: 10.1016/j.jorganchem.2017.09.028] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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44
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Higginbotham HF, Etherington MK, Monkman AP. Fluorescence and Phosphorescence Anisotropy from Oriented Films of Thermally Activated Delayed Fluorescence Emitters. J Phys Chem Lett 2017; 8:2930-2935. [PMID: 28548498 DOI: 10.1021/acs.jpclett.7b00729] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Anisotropy within three TADF materials has been observed using steady-state fluorescence polarization. This technique has allowed for the observation of differences in polarization within dilute solution, and both unstretched and stretched films; the latter producing highly aligned molecules within the sample. Using these aligned films differences in anisotropy can be observed between the emission from the 1LE and 1CT states and upon exciting different absorption bands. Furthermore, polarization observed from time-resolved measurements highlights the strong vibronic coupling between charge-transfer and local triplet states.
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Affiliation(s)
| | - Marc K Etherington
- Department of Physics, Durham University , South Road, Durham DH1 3LE, United Kingdom
| | - Andrew P Monkman
- Department of Physics, Durham University , South Road, Durham DH1 3LE, United Kingdom
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45
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Etherington MK, Franchello F, Gibson J, Northey T, Santos J, Ward JS, Higginbotham HF, Data P, Kurowska A, Dos Santos PL, Graves DR, Batsanov AS, Dias FB, Bryce MR, Penfold TJ, Monkman AP. Regio- and conformational isomerization critical to design of efficient thermally-activated delayed fluorescence emitters. Nat Commun 2017; 8:14987. [PMID: 28406153 PMCID: PMC5399286 DOI: 10.1038/ncomms14987] [Citation(s) in RCA: 186] [Impact Index Per Article: 26.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2016] [Accepted: 02/19/2017] [Indexed: 11/12/2022] Open
Abstract
Regio- and conformational isomerization are fundamental in chemistry, with profound effects upon physical properties, however their role in excited state properties is less developed. Here two regioisomers of bis(10H-phenothiazin-10-yl)dibenzo[b,d]thiophene-S,S-dioxide, a donor–acceptor–donor (D–A–D) thermally-activated delayed fluorescence (TADF) emitter, are studied. 2,8-bis(10H-phenothiazin-10-yl)dibenzo[b,d]thiophene-S,S-dioxide exhibits only one quasi-equatorial conformer on both donor sites, with charge-transfer (CT) emission close to the local triplet state leading to efficient TADF via spin-vibronic coupling. However, 3,7-bis(10H-phenothiazin-10-yl)dibenzo[b,d]thiophene-S,S-dioxide displays both a quasi-equatorial CT state and a higher-energy quasi-axial CT state. No TADF is observed in the quasi-axial CT emission. These two CT states link directly to the two folded conformers of phenothiazine. The presence of the low-lying local triplet state of the axial conformer also means that this quasi-axial CT is an effective loss pathway both photophysically and in devices. Importantly, donors or acceptors with more than one conformer have negative repercussions for TADF in organic light-emitting diodes. The search for brighter emitting materials is essential to the development of OLED devices. Etherington et al. show how the presence of two regioisomers of a donor-acceptor-donor thermally-activated delayed fluorescence molecule affects the device efficiency, with one acting as a triplet quencher.
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Affiliation(s)
- Marc K Etherington
- Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
| | - Flavio Franchello
- Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
| | - Jamie Gibson
- School of Chemistry, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
| | - Thomas Northey
- School of Chemistry, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
| | - Jose Santos
- Department of Chemistry, Durham University, South Road, Durham DH1 3LE, UK
| | - Jonathan S Ward
- Department of Chemistry, Durham University, South Road, Durham DH1 3LE, UK
| | | | - Przemyslaw Data
- Department of Physics, Durham University, South Road, Durham DH1 3LE, UK.,Faculty of Chemistry, Silesian University of Technology, Marcina Strzody 9, 44-100 Gliwice, Poland
| | - Aleksandra Kurowska
- Faculty of Chemistry, Silesian University of Technology, Marcina Strzody 9, 44-100 Gliwice, Poland
| | | | - David R Graves
- Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
| | - Andrei S Batsanov
- Department of Chemistry, Durham University, South Road, Durham DH1 3LE, UK
| | - Fernando B Dias
- Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
| | - Martin R Bryce
- Department of Chemistry, Durham University, South Road, Durham DH1 3LE, UK
| | - Thomas J Penfold
- School of Chemistry, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
| | - Andrew P Monkman
- Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
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46
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Okazaki M, Takeda Y, Data P, Pander P, Higginbotham H, Monkman AP, Minakata S. Thermally activated delayed fluorescent phenothiazine-dibenzo[ a, j]phenazine-phenothiazine triads exhibiting tricolor-changing mechanochromic luminescence. Chem Sci 2017; 8:2677-2686. [PMID: 28553504 PMCID: PMC5433494 DOI: 10.1039/c6sc04863c] [Citation(s) in RCA: 179] [Impact Index Per Article: 25.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2016] [Accepted: 01/07/2017] [Indexed: 12/24/2022] Open
Abstract
Novel U-shaped donor-acceptor-donor (D-A-D) π-conjugated multi-functional molecules comprising dibenzo[a,j]phenazine (DBPHZ) as an acceptor and phenothiazines (PTZ) as donors have been developed. Most importantly, the D-A-D compounds exhibit not only distinct tricolor-changeable mechanochromic luminescence (MCL) properties but also efficient thermally activated delayed fluorescence (TADF). Quantum chemical calculations, X-ray diffraction analysis, and systematic studies on the photophysical properties indicated that the "two-conformation-switchable" PTZ units play a highly important role in achieving multi-color-changing MCL. Time-resolved photophysical measurements revealed that the developed D-A-D compounds also exhibit efficient orange-TADF. Furthermore, organic light-emitting diode (OLED) devices fabricated with the new TADF emitters have achieved high external quantum efficiencies (EQEs) up to 16.8%, which significantly exceeds the theoretical maximum (∼5%) of conventional fluorescent emitters.
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Affiliation(s)
- Masato Okazaki
- Department of Applied Chemistry , Graduate School of Engineering , Osaka University , Yamadaoka 2-1, Suita , Osaka 565-0871 , Japan . ;
| | - Youhei Takeda
- Department of Applied Chemistry , Graduate School of Engineering , Osaka University , Yamadaoka 2-1, Suita , Osaka 565-0871 , Japan . ;
| | - Przemyslaw Data
- Physics Department , Durham University , South Road , Durham DH1 3LE , UK .
- Faculty of Chemistry , Silesian University of Technology , M. Stzody 9 , 44-100 Gliwice , Poland
| | - Piotr Pander
- Physics Department , Durham University , South Road , Durham DH1 3LE , UK .
- Faculty of Chemistry , Silesian University of Technology , M. Stzody 9 , 44-100 Gliwice , Poland
| | | | - Andrew P Monkman
- Physics Department , Durham University , South Road , Durham DH1 3LE , UK .
| | - Satoshi Minakata
- Department of Applied Chemistry , Graduate School of Engineering , Osaka University , Yamadaoka 2-1, Suita , Osaka 565-0871 , Japan . ;
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47
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48
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Benjamin H, Fox MA, Batsanov AS, Al-Attar HA, Li C, Ren Z, Monkman AP, Bryce MR. Pyridylpyrazole N^N ligands combined with sulfonyl-functionalised cyclometalating ligands for blue-emitting iridium(iii) complexes and solution-processable PhOLEDs. Dalton Trans 2017; 46:10996-11007. [DOI: 10.1039/c7dt02289a] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
A blue phosphorescent emitter for PhOLEDs with brightness of 5400 cd m−2 at 10 V and λELmax 460 nm, CIEx,y (0.15, 0.21).
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Affiliation(s)
- Helen Benjamin
- Department of Chemistry
- Durham University
- Durham DH1 3LE
- UK
| | - Mark A. Fox
- Department of Chemistry
- Durham University
- Durham DH1 3LE
- UK
| | | | | | - Chensen Li
- State Key Laboratory of Chemical Resource Engineering
- Beijing University of Chemical Technology
- Beijing 100029
- China
| | - Zhongjie Ren
- State Key Laboratory of Chemical Resource Engineering
- Beijing University of Chemical Technology
- Beijing 100029
- China
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49
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Costa BBA, Jardim GAM, Santos PL, Calado HDR, Monkman AP, Dias FB, da Silva Júnior EN, Cury LA. Indirect consequences of exciplex states on the phosphorescence lifetime of phenazine-based 1,2,3-triazole luminescent probes. Phys Chem Chem Phys 2017; 19:3473-3479. [DOI: 10.1039/c6cp06134f] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Exciplex formation, and delayed fluorescence and phosphorescence interplay interactions were investigated in phenazine derivative solutions at room temperature.
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Affiliation(s)
- Bárbara B. A. Costa
- Instituto de Ciências Exatas
- Departamento de Física
- Universidade Federal de Minas Gerais
- Belo Horizonte
- Brazil
| | - Guilherme A. M. Jardim
- Instituto de Ciências Exatas
- Departamento de Química
- Universidade Federal de Minas Gerais
- Belo Horizonte
- Brazil
| | | | - Hállen D. R. Calado
- Instituto de Ciências Exatas
- Departamento de Química
- Universidade Federal de Minas Gerais
- Belo Horizonte
- Brazil
| | | | | | | | - Luiz A. Cury
- Instituto de Ciências Exatas
- Departamento de Física
- Universidade Federal de Minas Gerais
- Belo Horizonte
- Brazil
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Dias FB, Santos J, Graves DR, Data P, Nobuyasu RS, Fox MA, Batsanov AS, Palmeira T, Berberan‐Santos MN, Bryce MR, Monkman AP. The Role of Local Triplet Excited States and D-A Relative Orientation in Thermally Activated Delayed Fluorescence: Photophysics and Devices. Adv Sci (Weinh) 2016; 3:1600080. [PMID: 27981000 PMCID: PMC5157178 DOI: 10.1002/advs.201600080] [Citation(s) in RCA: 135] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2016] [Revised: 05/19/2016] [Indexed: 05/20/2023]
Abstract
Here, a comprehensive photophysical investigation of a the emitter molecule DPTZ-DBTO2, showing thermally activated delayed fluorescence (TADF), with near-orthogonal electron donor (D) and acceptor (A) units is reported. It is shown that DPTZ-DBTO2 has minimal singlet-triplet energy splitting due to its near-rigid molecular geometry. However, the electronic coupling between the local triplet (3LE) and the charge transfer states, singlet and triplet, (1CT, 3CT), and the effect of dynamic rocking of the D-A units about the orthogonal geometry are crucial for efficient TADF to be achieved. In solvents with low polarity, the guest emissive singlet 1CT state couples directly to the near-degenerate 3LE, efficiently harvesting the triplet states by a spin orbit coupling charge transfer mechanism (SOCT). However, in solvents with higher polarity the emissive CT state in DPTZ-DBTO2 shifts below (the static) 3LE, leading to decreased TADF efficiencies. The relatively large energy difference between the 1CT and 3LE states and the extremely low efficiency of the 1CT to 3CT hyperfine coupling is responsible for the reduction in TADF efficiency. Both the electronic coupling between 1CT and 3LE, and the (dynamic) orientation of the D-A units are thus critical elements that dictate reverse intersystem crossing processes and thus high efficiency in TADF.
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Affiliation(s)
| | - Jose Santos
- Physics DepartmentDurham UniversitySouth RoadDurhamDH1 3LEUK
- IMDEA NanocienciaC/Faraday, 9Campus Universitario de Cantoblanco28049MadridSpain
| | - David R. Graves
- Physics DepartmentDurham UniversitySouth RoadDurhamDH1 3LEUK
| | - Przemyslaw Data
- Physics DepartmentDurham UniversitySouth RoadDurhamDH1 3LEUK
- Faculty of ChemistrySilesian University of TechnologyM. Strzody 944‐100GliwicePoland
| | | | - Mark A. Fox
- Chemistry DepartmentDurham UniversitySouth RoadDurhamDH1 3LEUK
| | | | - Tiago Palmeira
- Centro de Quimica‐Fisica MolecularInstituto Superior Tecnico1049‐001LisboaPortugal
| | | | - Martin R. Bryce
- Chemistry DepartmentDurham UniversitySouth RoadDurhamDH1 3LEUK
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