1
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Govindharaj P, Wierzba AJ, Kęska K, Kochman MA, Wiosna-Sałyga G, Kubas A, Data P, Lindner M. Regioisomerism vs Conformation: Impact of Molecular Design on the Emission Pathway in Organic Light-Emitting Device Emitters. ACS APPLIED MATERIALS & INTERFACES 2024; 16. [PMID: 38668584 PMCID: PMC11082840 DOI: 10.1021/acsami.3c19212] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2023] [Revised: 04/14/2024] [Accepted: 04/17/2024] [Indexed: 05/12/2024]
Abstract
Despite the design and proposal of several new structural motifs as thermally activated delayed fluorescent (TADF) emitters for organic light-emitting device (OLED) applications, the nature of their interaction with the host matrix in the emissive layer of the device and their influence on observed photophysical outputs remain unclear. To address this issue, we present, for the first time, the use of up to four regioisomers bearing a donor-acceptor-donor electronic structure based on the desymmetrized naphthalene benzimidazole scaffold, equipped with various electron-donating units and possessing distinguished conformational lability. Quantum chemical calculations allow us to identify the most favorable conformations adopted by the electron-rich groups across the entire pool of regioisomers. These conformations were then compared with conformational changes caused by the interaction of the emitter with the Zeonex and 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP) matrices, and the correlation with observed photophysics was monitored by UV-vis absorption and steady-state photoluminescence spectra, combined with time-resolved spectroscopic techniques. Importantly, a CBP matrix was found to have a significant impact on the conformational change of regioisomers, leading to unique TADF emission mechanisms that encompass dual emission and inversion of the singlet-triplet excited-state energies and result in the enhancement of TADF efficiency. As a proof of concept, regioisomers with optimal donor positions were utilized to fabricate an OLED, revealing, with the best-performing dye, an external quantum emission of 11.6%, accompanied by remarkable luminance (28,000 cd/m2). These observations lay the groundwork for a better understanding of the role of the host matrix. In the long term, this new knowledge can lead to predicting the influence of the host matrix and adopting the structure of the emitter in a way that allows the development of highly efficient and efficient OLEDs.
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Affiliation(s)
- Prasannamani Govindharaj
- Department
of Molecular Physics, Faculty of Chemistry, Łódź University of Technology, Stefana Żeromskiego 114, 90-543 Łódź, Poland
| | - Aleksandra J. Wierzba
- Institute
of Organic Chemistry, Polish Academy of
Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
| | - Karolina Kęska
- Institute
of Organic Chemistry, Polish Academy of
Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
| | - Michał Andrzej Kochman
- Institute
of Physical Chemistry, Polish Academy of
Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
| | - Gabriela Wiosna-Sałyga
- Department
of Molecular Physics, Faculty of Chemistry, Łódź University of Technology, Stefana Żeromskiego 114, 90-543 Łódź, Poland
| | - Adam Kubas
- Institute
of Physical Chemistry, Polish Academy of
Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
| | - Przemysław Data
- Department
of Molecular Physics, Faculty of Chemistry, Łódź University of Technology, Stefana Żeromskiego 114, 90-543 Łódź, Poland
| | - Marcin Lindner
- Institute
of Organic Chemistry, Polish Academy of
Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
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2
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Di Maiolo F, Phan Huu DKA, Giavazzi D, Landi A, Racchi O, Painelli A. Shedding light on thermally-activated delayed fluorescence. Chem Sci 2024; 15:5434-5450. [PMID: 38638233 PMCID: PMC11023041 DOI: 10.1039/d4sc00033a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2024] [Accepted: 02/17/2024] [Indexed: 04/20/2024] Open
Abstract
Thermally activated delayed fluorescence (TADF) is a hot research topic in view of its impressive applications in a wide variety of fields from organic LEDs to photodynamic therapy and metal-free photocatalysis. TADF is a rare and fragile phenomenon that requires a delicate equilibrium between tiny singlet-triplet gaps, sizable spin-orbit couplings, conformational flexibility and a balanced contribution of charge transfer and local excited states. To make the picture more complex, this precarious equilibrium is non-trivially affected by the interaction of the TADF dye with its local environment. The concurrent optimization of the dye and of the embedding medium is therefore of paramount importance to boost practical applications of TADF. Towards this aim, refined theoretical and computational approaches must be cleverly exploited, paying attention to the reliability of adopted approximations. In this perspective, we will address some of the most important issues in the field. Specifically, we will critically review theoretical and computational approaches to TADF rates, highlighting the limits of widespread approaches. Environmental effects on the TADF photophysics are discussed in detail, focusing on the major role played by dielectric and conformational disorder in liquid solutions and amorphous matrices.
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Affiliation(s)
- Francesco Di Maiolo
- Dept. Chemistry, Life Science and Environmental Sustainability, University of Parma Parco Area delle Scienze 17/A 43124 Parma Italy
| | - D K Andrea Phan Huu
- Dept. Chemistry, Life Science and Environmental Sustainability, University of Parma Parco Area delle Scienze 17/A 43124 Parma Italy
| | - Davide Giavazzi
- Dept. Chemistry, Life Science and Environmental Sustainability, University of Parma Parco Area delle Scienze 17/A 43124 Parma Italy
| | - Andrea Landi
- Dept. Chemistry, Life Science and Environmental Sustainability, University of Parma Parco Area delle Scienze 17/A 43124 Parma Italy
| | - Ottavia Racchi
- Dept. Chemistry, Life Science and Environmental Sustainability, University of Parma Parco Area delle Scienze 17/A 43124 Parma Italy
| | - Anna Painelli
- Dept. Chemistry, Life Science and Environmental Sustainability, University of Parma Parco Area delle Scienze 17/A 43124 Parma Italy
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3
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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] [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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4
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Chen G, Swartzfager JR, Asbury JB. Matrix Dynamics and Their Crucial Role in Non-radiative Decay during Thermally Activated Delayed Fluorescence. J Am Chem Soc 2023; 145:25495-25504. [PMID: 37955854 DOI: 10.1021/jacs.3c11719] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2023]
Abstract
We investigated the interplay of matrix dynamics with the molecular dynamics of a thermally activated delayed fluorescence (TADF) emitter, NAI-DMAC, to identify factors that influence the photophysical processes leading to TADF. The matrix dynamics surrounding NAI-DMAC molecules were varied continuously from the liquid to the solid state by depositing toluene solutions containing poly(methyl methacrylate) (PMMA) and NAI-DMAC onto optical substrates. We monitored changes of the NAI-DMAC emission as the liquid films dried to form solid PMMA films using temperature- and time-resolved photoluminescence spectroscopy. We observed that, in low-viscosity solutions, the proportion of delayed fluorescence from NAI-DMAC was much smaller than that of prompt fluorescence, indicating that negligible TADF occurred in the low-viscosity environment. However, as the viscosity of the environment diverged at the final stages of dry-down to form solid PMMA films, the delayed fluorescence component of NAI-DMAC emission was extended to longer time scales and increased in amplitude relative to prompt emission as the temperature increased─signatures that TADF occurred in the solid state as expected. Our findings reveal the influence that matrix dynamics have on the competition between conformational motion needed to access emissive states and undergo TADF versus larger amplitude structural fluctuations that lead to non-radiative decay. Insights from these studies will inform ongoing work to understand and predict how host matrices used in organic light-emitting devices can be designed to maximize the radiative properties of TADF emitters by allowing molecular motion needed to undergo TADF while restricting larger amplitude motion leading to non-radiative decay.
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Affiliation(s)
- Gary Chen
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - John R Swartzfager
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - John B Asbury
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
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5
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Hepguler A, Ulukan P, Catak S. The photophysical properties of sulfone-based TADF emitters in relation to their structural properties. Phys Chem Chem Phys 2023; 25:31457-31470. [PMID: 37962481 DOI: 10.1039/d3cp03557c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2023]
Abstract
In this work, thermally activated delayed fluorescence (TADF) of a series of emitters with sulfone-based acceptor moieties was studied by density functional theory (DFT) methods. Sulfone derivatives were shown to be high performing TADF emitters over recent years. When discussing the TADF efficiency, various properties, such as the singlet-triplet energy gap (ΔEST), spin-orbit coupling (SOC) and the nature of states, stand out due to their roles in reverse intersystem crossing (RISC). Here, we mainly focused on three important structural parameters that affect the intersystem crossing (ISC) and RISC pathways and their efficiencies. These three parameters are: (1) the effect of meta- and para-conjugation, (2) the effect of rigid acceptor moieties and (3) the effect of the phenyl bridge on photophysical properties.
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Affiliation(s)
- Aslıhan Hepguler
- Department of Chemistry, Bogazici University, Bebek, 34342, Istanbul, Turkey.
| | - Pelin Ulukan
- Department of Chemistry, Bogazici University, Bebek, 34342, Istanbul, Turkey.
| | - Saron Catak
- Department of Chemistry, Bogazici University, Bebek, 34342, Istanbul, Turkey.
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6
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Bardi B, Giavazzi D, Ferrari E, Iagatti A, Di Donato M, Phan Huu DKA, Di Maiolo F, Sissa C, Masino M, Lapini A, Painelli A. Solid state solvation: a fresh view. MATERIALS HORIZONS 2023; 10:4172-4182. [PMID: 37522331 DOI: 10.1039/d3mh00988b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/01/2023]
Abstract
The design of efficient organic electronic devices, including OLEDs, OPVs, luminescent solar concentrators, etc., relies on the optimization of relevant materials, often constituted by an active (functional) dye embedded in a matrix. Understanding solid state solvation (SSS), i.e. how the properties of the active dye are affected by the matrix, is therefore an issue of fundamental and technological relevance. Here an extensive experimental and theoretical investigation is presented shedding light on this, somewhat controversial, topic. The spectral properties of the dye at equilibrium, i.e. absorption and Raman spectra, are not affected by the matrix dynamics. Reliable estimates of the matrix polarity are then obtained from an analysis of the micro-Raman spectra of polar dyes. Specifically, to establish a reliable polarity scale, the spectra of DCM or NR dispersed in amorphous matrices are compared with the spectra of the same dyes in liquid solvents with known polarity. On the other hand, steady-state emission spectra obtained in solid matrices depend in a highly non-trivial way on the matrix polarity and its dynamics. An extensive experimental and theoretical analysis of the time-resolved emission spectra of NR in a very large time window (15 fs-15 ns) allows us to validate this dye as a good probe of the dielectric dynamics of the surrounding medium. We provide a first assessment of the relaxation dynamics of two matrices (mCBPCN and DPEPO) of interest for OLED application, unambiguously demonstrating that the matrix readjusts for at least 15 ns after the dye photoexcitation.
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Affiliation(s)
- Brunella Bardi
- Dept. Chemistry, Life Science and Environmental Sustainability, University of Parma, Parco Area delle Scienze 17/A, 43124 Parma, Italy.
| | - Davide Giavazzi
- Dept. Chemistry, Life Science and Environmental Sustainability, University of Parma, Parco Area delle Scienze 17/A, 43124 Parma, Italy.
| | - Elena Ferrari
- Dept. Chemistry, Life Science and Environmental Sustainability, University of Parma, Parco Area delle Scienze 17/A, 43124 Parma, Italy.
| | - Alessandro Iagatti
- CNR-INO (Istituto Nazionaledi Ottica), Largo Fermi 6, 50125 Firenze, Italy
- LENS (European Laboratory for Non-Linear Spectroscopy), Via N. Carrara 1, 50019, Sesto Fiorentino, FI, Italy
| | - Mariangela Di Donato
- LENS (European Laboratory for Non-Linear Spectroscopy), Via N. Carrara 1, 50019, Sesto Fiorentino, FI, Italy
- ICCOM-CNR, via Madonna del Piano 10, I-50019 Sesto Fiorentino, FI, Italy
| | - D K Andrea Phan Huu
- Dept. Chemistry, Life Science and Environmental Sustainability, University of Parma, Parco Area delle Scienze 17/A, 43124 Parma, Italy.
| | - Francesco Di Maiolo
- Dept. Chemistry, Life Science and Environmental Sustainability, University of Parma, Parco Area delle Scienze 17/A, 43124 Parma, Italy.
| | - Cristina Sissa
- Dept. Chemistry, Life Science and Environmental Sustainability, University of Parma, Parco Area delle Scienze 17/A, 43124 Parma, Italy.
| | - Matteo Masino
- Dept. Chemistry, Life Science and Environmental Sustainability, University of Parma, Parco Area delle Scienze 17/A, 43124 Parma, Italy.
| | - Andrea Lapini
- Dept. Chemistry, Life Science and Environmental Sustainability, University of Parma, Parco Area delle Scienze 17/A, 43124 Parma, Italy.
- LENS (European Laboratory for Non-Linear Spectroscopy), Via N. Carrara 1, 50019, Sesto Fiorentino, FI, Italy
| | - Anna Painelli
- Dept. Chemistry, Life Science and Environmental Sustainability, University of Parma, Parco Area delle Scienze 17/A, 43124 Parma, Italy.
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7
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Sivasakthi P, Jacob JM, Ravva MK, Samanta PK. Theoretical Insights into the Optical and Excited State Properties of Donor-Phenyl Bridge-Acceptor Containing Through-Space Charge Transfer Molecules. J Phys Chem A 2023; 127:886-893. [PMID: 36653147 DOI: 10.1021/acs.jpca.2c07055] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
A comparative new strategy to enhance thermally activated delayed fluorescence (TADF) of through-space charge transfer (CT) molecules in organic light-emitting diodes (OLEDs) is investigated. Generally, TADF molecules adopt a twisted donor and acceptor structure to get a sufficiently small ΔEST and a higher value of the spin-orbit coupling matrix element (SOCME). However, molecules containing donor-phenyl bridge-acceptor (D-p-A) units and featuring π-stacked architectures have intramolecular CT contribution through space and exhibit high TADF efficiency. We have explored the insights into the TADF mechanism in D-p-A molecules using the density functional theory (DFT) and time-dependent DFT methods. The calculated optical absorption and ΔEST values are found to be in good agreement with available experimental data. Interestingly, we found the origin of the SOCME to be the twisted orientation of the donor and bridge moieties. Also, we predicted similar molecules with enhanced OLED efficiency with different substitutions.
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Affiliation(s)
- Pandiyan Sivasakthi
- Department of Chemistry, School of Science, GITAM University, Hyderabad502329, India
| | - Jesni M Jacob
- Department of Chemistry, SRM University-AP, Amaravati522240, Andhra Pradesh, India
| | - Mahesh Kumar Ravva
- Department of Chemistry, SRM University-AP, Amaravati522240, Andhra Pradesh, India
| | - Pralok K Samanta
- Department of Chemistry, School of Science, GITAM University, Hyderabad502329, India
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8
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Swartzfager JR, Chen G, Francese T, Galli G, Asbury JB. Interplay of molecular dynamics and radiative decay of a TADF emitter in a glass-forming liquid. Phys Chem Chem Phys 2023; 25:3151-3159. [PMID: 36621848 DOI: 10.1039/d2cp05138a] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
We investigate the role of molecular dynamics in the luminescent properties of a prototypical thermally activated delayed fluorescence (TADF) emitter, NAI-DMAC, in solution using a combination of temperature dependent time-resolved photoluminescence and absorption spectroscopies. We use a glass forming liquid, 2-methylfuran, to introduce an abrupt change in the temperature dependent diffusion dynamics of the solvent and examine the influence this has on the emission intensity of NAI-DMAC molecules. Comparison of experiment with first principles molecular dynamics simulations reveals that the emission intensity of NAI-DMAC molecules follows the temperature-dependent self-diffusion dynamics of the solvent. A marked reduction of emission intensity is observed as the temperature decreases toward the glass transition because the rate at which NAI-DMAC molecules can access emissive molecular conformations is greatly reduced. Below the glass transition, the diffusion dynamics of the solvent changes more slowly with temperature, which causes the emission intensity to decrease more slowly as well. The combination of experiment and computation suggests a pathway by which TADF emitters may transiently access a distribution of conformational states and avoid the need for an average conformation that strikes a balance between lower singlet-triplet energy splittings versus higher emission probabilities.
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Affiliation(s)
- John R Swartzfager
- Department of Chemistry, The Pennsylvania State University, University Park, PA, 16802, USA.
| | - Gary Chen
- Department of Chemistry, The Pennsylvania State University, University Park, PA, 16802, USA.
| | - Tommaso Francese
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL, 60637, USA
| | - Giulia Galli
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL, 60637, USA.,Materials Science Division and Center for Molecular Engineering, Argonne National Laboratory, Lemont, IL, 60439, USA.,Department of Chemistry, University of Chicago, Chicago, IL, 60637, USA
| | - John B Asbury
- Department of Chemistry, The Pennsylvania State University, University Park, PA, 16802, USA.
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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] [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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Phan Huu DKA, Saseendran S, Dhali R, Franca LG, Stavrou K, Monkman A, Painelli A. Thermally Activated Delayed Fluorescence: Polarity, Rigidity, and Disorder in Condensed Phases. J Am Chem Soc 2022; 144:15211-15222. [PMID: 35944182 PMCID: PMC9413221 DOI: 10.1021/jacs.2c05537] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
We present a detailed and comprehensive picture of the photophysics of thermally activated delayed fluorescence (TADF). The approach relies on a few-state model, parametrized ab initio on a prototypical TADF dye, that explicitly accounts for the nonadiabatic coupling between electrons and vibrational and conformational motion, crucial to properly address (reverse) intersystem crossing rates. The Onsager model is exploited to account for the medium polarity and polarizability, with careful consideration of the different time scales of relevant degrees of freedom. TADF photophysics is then quantitatively addressed in a coherent and exhaustive approach that accurately reproduces the complex temporal evolution of emission spectra in liquid solvents as well as in solid organic matrices. The different rigidity of the two environments is responsible for the appearance in matrices of important inhomogeneous broadening phenomena that are ascribed to the intertwined contribution from (quasi)static conformational and dielectric disorder.
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Affiliation(s)
- D K Andrea Phan Huu
- Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, 43124 Parma, Italy
| | - Sangeeth Saseendran
- Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, 43124 Parma, Italy
| | - Rama Dhali
- Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, 43124 Parma, Italy
| | | | - Kleitos Stavrou
- Department of Physics, Durham University, South Road, Durham DH1 3LE, U.K
| | - Andrew Monkman
- Department of Physics, Durham University, South Road, Durham DH1 3LE, U.K
| | - Anna Painelli
- Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, 43124 Parma, Italy
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11
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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: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [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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12
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Wang Y, Wu W, Choy KL. The optical spectra of DMAC based molecules for organic light‐emitting diodes: Hybrid‐exchange density functional theory study. J PHYS ORG CHEM 2022; 35:e4386. [PMID: 36246346 PMCID: PMC9541038 DOI: 10.1002/poc.4386] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2022] [Revised: 04/11/2022] [Accepted: 05/18/2022] [Indexed: 11/24/2022]
Abstract
Organic light‐emitting diodes (OLED) have considerable advantages over the conventional counterpart. Molecular design by simulations is important for the discovery of new material candidate to improve the performance of OLED. Recently, thermally assisted delayed fluorescence OLED based on DMAC (9,9‐dimethyl‐9,10‐dihydroacridine)‐related molecules have been found to have superior performance. In this work, a series of first‐principles calculations are performed on DMAC‐DPS (diphenylsulfone, emission of blue‐color light), DMAC‐BP (benzophenone, green), DMAC‐DCPP (dicyclohexylphosphonium, red), and the newly designed DMAC‐BF (enaminone difluoroboron complexes, red) molecules, based on time‐dependent density‐functional theory, the hybrid‐exchange density functional, and the long‐range corrected hybrid‐exchange density functional. By varying the percentage of Hartree–Fock (HF) exchange in the hybrid‐exchange functional, the emission spectra can be over 97% fitted to the experimental results. We found that the fitted proportion of HF will increase as the wavelengths of the molecules decrease (30% for DPS, 20% for BP, and 10% for DCPP). By contrast, the long‐range corrected hybrid‐exchange density functional can lead to a good estimate on the absorption spectra. In addition, we have also applied our fitting computational procedure to the newly designed molecule. The molecular orbitals involved in the related excited states have also been investigated for these molecules, which show a common charge‐transfer characteristic between the acceptor part (DPS/BP/DCPP/BF) and the donor (DMAC).
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Affiliation(s)
- Yuting Wang
- UCL Institute for Materials Discovery, University College London London United Kingdom
| | - Wei Wu
- UCL Institute for Materials Discovery, University College London London United Kingdom
| | - Kwang Leong Choy
- UCL Institute for Materials Discovery, University College London London United Kingdom
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13
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Carreras A, Casanova D. Theory of exciton dynamics in thermally activated delayed fluorescence. CHEMPHOTOCHEM 2022. [DOI: 10.1002/cptc.202200066] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
| | - David Casanova
- Donostia International Physics Center Donostia International Physics Center Paseo Manuel Lardizabal,4 20018 San Sebastián SPAIN
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14
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Intersystem Crossing in Boron-Based Donor-Spiro-Acceptor Organic Chromophore: A Detailed Theoretical Study. J Phys Chem A 2021; 125:6674-6680. [PMID: 34343011 DOI: 10.1021/acs.jpca.1c03729] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Intersystem crossing and reverse intersystem crossing (rISC) processes were investigated in a boron-based donor-spiro-acceptor organic chromophore which shows thermally activated delayed fluorescence. Due to the perpendicular arrangement between donor and acceptor moieties, the HOMO and the LUMO are spatially separated, and the compound shows charge transfer (CT) transitions. We found both S1 and T1 excited states are CT in nature (i.e., electron and hole wave functions are localized on acceptor and donor units, respectively) and T2, which is higher in energy than S1 and T1, is locally excited in nature (i.e., both electron and hole wave functions are localized on an acceptor unit). Because of the same nature of excitation (i.e., CT here), the spin-orbit coupling matrix element between S1 and T1 is very low and insignificant exciton conversion occurs from the T1 state to the S1 state (and vice versa). Our combined time-dependent density functional theory and quantum dynamics simulation shows that the rISC process from the T1 state to the S1 state can be enhanced by the presence of a nearby local excited triplet state (i.e., T2 state here). A smaller gap between the T1 and T2 states efficiently establishes the rISC route.
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Eng J, Penfold TJ. Open questions on the photophysics of thermally activated delayed fluorescence. Commun Chem 2021; 4:91. [PMID: 36697585 PMCID: PMC9814861 DOI: 10.1038/s42004-021-00533-y] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2021] [Accepted: 05/27/2021] [Indexed: 01/28/2023] Open
Affiliation(s)
- Julien Eng
- grid.1006.70000 0001 0462 7212Chemistry, School of Natural and Environmental Sciences, Newcastle University, Newcastle Upon Tyne, UK
| | - Thomas J. Penfold
- grid.1006.70000 0001 0462 7212Chemistry, School of Natural and Environmental Sciences, Newcastle University, Newcastle Upon Tyne, UK
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16
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Dhali R, Phan Huu DKA, Terenziani F, Sissa C, Painelli A. Thermally activated delayed fluorescence: A critical assessment of environmental effects on the singlet-triplet energy gap. J Chem Phys 2021; 154:134112. [PMID: 33832272 DOI: 10.1063/5.0042058] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The effective design of dyes optimized for thermally activated delayed fluorescence (TADF) requires the precise control of two tiny energies: the singlet-triplet gap, which has to be maintained within thermal energy, and the strength of spin-orbit coupling. A subtle interplay among low-energy excited states having dominant charge-transfer and local character then governs TADF efficiency, making models for environmental effects both crucial and challenging. The main message of this paper is a warning to the community of chemists, physicists, and material scientists working in the field: the adiabatic approximation implicitly imposed to the treatment of fast environmental degrees of freedom in quantum-classical and continuum solvation models leads to uncontrolled results. Several approximation schemes were proposed to mitigate the issue, but we underline that the adiabatic approximation to fast solvation is inadequate and cannot be improved; rather, it must be abandoned in favor of an antiadiabatic approach.
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Affiliation(s)
- Rama Dhali
- Department of Chemistry, Life Science and Environmental Sustainability, University of Parma, Parma, Italy
| | - D K Andrea Phan Huu
- Department of Chemistry, Life Science and Environmental Sustainability, University of Parma, Parma, Italy
| | - Francesca Terenziani
- Department of Chemistry, Life Science and Environmental Sustainability, University of Parma, Parma, Italy
| | - Cristina Sissa
- Department of Chemistry, Life Science and Environmental Sustainability, University of Parma, Parma, Italy
| | - Anna Painelli
- Department of Chemistry, Life Science and Environmental Sustainability, University of Parma, Parma, Italy
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