1
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Cho HH, Congrave DG, Gillett AJ, Montanaro S, Francis HE, Riesgo-Gonzalez V, Ye J, Chowdury R, Zeng W, Etherington MK, Royakkers J, Millington O, Bond AD, Plasser F, Frost JM, Grey CP, Rao A, Friend RH, Greenham NC, Bronstein H. Suppression of Dexter transfer by covalent encapsulation for efficient matrix-free narrowband deep blue hyperfluorescent OLEDs. Nat Mater 2024; 23:519-526. [PMID: 38480865 PMCID: PMC10990937 DOI: 10.1038/s41563-024-01812-4] [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] [Subscribe] [Scholar Register] [Received: 02/28/2023] [Accepted: 01/18/2024] [Indexed: 03/21/2024]
Abstract
Hyperfluorescence shows great promise for the next generation of commercially feasible blue organic light-emitting diodes, for which eliminating the Dexter transfer to terminal emitter triplet states is key to efficiency and stability. Current devices rely on high-gap matrices to prevent Dexter transfer, which unfortunately leads to overly complex devices from a fabrication standpoint. Here we introduce a molecular design where ultranarrowband blue emitters are covalently encapsulated by insulating alkylene straps. Organic light-emitting diodes with simple emissive layers consisting of pristine thermally activated delayed fluorescence hosts doped with encapsulated terminal emitters exhibit negligible external quantum efficiency drops compared with non-doped devices, enabling a maximum external quantum efficiency of 21.5%. To explain the high efficiency in the absence of high-gap matrices, we turn to transient absorption spectroscopy. It is directly observed that Dexter transfer from a pristine thermally activated delayed fluorescence sensitizer host can be substantially reduced by an encapsulated terminal emitter, opening the door to highly efficient 'matrix-free' blue hyperfluorescence.
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Affiliation(s)
- Hwan-Hee Cho
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | - Daniel G Congrave
- Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK.
| | | | - Stephanie Montanaro
- Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK
| | - Haydn E Francis
- Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK
- The Faraday Institution, Quad One, Harwell Science and Innovation Campus, Didcot, UK
| | - Víctor Riesgo-Gonzalez
- Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK
- The Faraday Institution, Quad One, Harwell Science and Innovation Campus, Didcot, UK
| | - Junzhi Ye
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | | | - Weixuan Zeng
- Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK
| | - Marc K Etherington
- Department of Mathematics, Physics and Electrical Engineering, Northumbria University, Ellison Place, Newcastle upon Tyne, UK
| | - Jeroen Royakkers
- Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK
| | - Oliver Millington
- Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK
| | - Andrew D Bond
- Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK
| | - Felix Plasser
- Department of Chemistry, Loughborough University, Loughborough, UK
| | | | - Clare P Grey
- Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK
- The Faraday Institution, Quad One, Harwell Science and Innovation Campus, Didcot, UK
| | - Akshay Rao
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | | | - Neil C Greenham
- Cavendish Laboratory, University of Cambridge, Cambridge, UK.
| | - Hugo Bronstein
- Cavendish Laboratory, University of Cambridge, Cambridge, UK.
- Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK.
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2
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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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3
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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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4
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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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5
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Abstract
Emitters that exhibit thermally activated delayed fluorescence (TADF) are of interest for commercial applications in organic light-emitting diodes (OLEDs) due to their ability to achieve internal quantum efficiency of 100%. However, beyond the intrinsic properties of these materials it is important to understand how the molecules interact with each other and when these interactions may occur. Such interactions lead to a significant red shift in the photoluminescence and electroluminescence, making them less practicable for commercial use. Through summarizing the literature, covering solid-state solvation effects and aggregate effects in organic emitters, this mini review outlines a framework for the complete study of TADF emitters formed from the current-state-of-the-art techniques.
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Affiliation(s)
- Marc K. Etherington
- Department of Mathematics, Physics and Electrical Engineering, Northumbria University, Newcastle upon Tyne, United Kingdom
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6
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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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7
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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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8
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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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9
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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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10
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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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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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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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Etherington MK, Gibson J, Higginbotham HF, Penfold TJ, Monkman AP. Revealing the spin-vibronic coupling mechanism of thermally activated delayed fluorescence. Nat Commun 2016; 7:13680. [PMID: 27901046 PMCID: PMC5141373 DOI: 10.1038/ncomms13680] [Citation(s) in RCA: 359] [Impact Index Per Article: 44.9] [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: 08/08/2016] [Accepted: 10/25/2016] [Indexed: 12/14/2022] Open
Abstract
Knowing the underlying photophysics of thermally activated delayed fluorescence (TADF) allows proper design of high efficiency organic light-emitting diodes. We have proposed a model to describe reverse intersystem crossing (rISC) in donor-acceptor charge transfer molecules, where spin-orbit coupling between singlet and triplet states is mediated by one of the local triplet states of the donor (or acceptor). This second order, vibronically coupled mechanism describes the basic photophysics of TADF. Through a series of measurements, whereby the energy ordering of the charge transfer (CT) excited states and the local triplet are tuned in and out of resonance, we show that TADF reaches a maximum at the resonance point, substantiating our model of rISC. Moreover, using photoinduced absorption, we show how the populations of both singlet and triplet CT states and the local triplet state change in and out of resonance. Our vibronic coupling rISC model is used to predict this behaviour and describes how rISC and TADF are affected by external perturbation.
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Affiliation(s)
- Marc K Etherington
- 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 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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