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Abdelmagid AG, Qureshi HA, Papachatzakis MA, Siltanen O, Kumar M, Ashokan A, Salman S, Luoma K, Daskalakis KS. Identifying the origin of delayed electroluminescence in a polariton organic light-emitting diode. NANOPHOTONICS 2024; 13:2565-2573. [PMID: 38836100 PMCID: PMC11147497 DOI: 10.1515/nanoph-2023-0587] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/12/2023] [Accepted: 12/04/2023] [Indexed: 06/06/2024]
Abstract
Modifying the energy landscape of existing molecular emitters is an attractive challenge with favourable outcomes in chemistry and organic optoelectronic research. It has recently been explored through strong light-matter coupling studies where the organic emitters were placed in an optical cavity. Nonetheless, a debate revolves around whether the observed change in the material properties represents novel coupled system dynamics or the unmasking of pre-existing material properties induced by light-matter interactions. Here, for the first time, we examined the effect of strong coupling in polariton organic light-emitting diodes via time-resolved electroluminescence studies. We accompanied our experimental analysis with theoretical fits using a model of coupled rate equations accounting for all major mechanisms that can result in delayed electroluminescence in organic emitters. We found that in our devices the delayed electroluminescence was dominated by emission from trapped charges and this mechanism remained unmodified in the presence of strong coupling.
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Affiliation(s)
| | - Hassan A. Qureshi
- Department of Mechanical and Materials Engineering, University of Turku, Turku, Finland
| | | | - Olli Siltanen
- Department of Mechanical and Materials Engineering, University of Turku, Turku, Finland
| | - Manish Kumar
- Department of Mechanical and Materials Engineering, University of Turku, Turku, Finland
| | - Ajith Ashokan
- Chemistry Department, Clark Atlanta University, Atlanta, GA30314, USA
| | - Seyhan Salman
- Chemistry Department, Clark Atlanta University, Atlanta, GA30314, USA
| | - Kimmo Luoma
- Department of Physics and Astronomy, University of Turku, Turku, Finland
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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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Wang L, Ge Z, Xu L, Song Y. An effective method in modulating thermally activated delayed fluorescence (TADF) emitters from green to blue emission: the role of the phenyl ring. Phys Chem Chem Phys 2024; 26:5597-5606. [PMID: 38285054 DOI: 10.1039/d3cp05632e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2024]
Abstract
Developing efficient blue emitters with high performance and low cost is crucial for the further development of organic light-emitting diodes (OLEDs). Based on the two experimentally reported green thermally activated delayed fluorescence (TADF) emitters, which are thioxanthone derivatives consisting of carbazole as an electron donor and 9H-thioxanthen-9-one-S,S-dioxide (SOXO) as an electron acceptor with donor-acceptor (D-A) or donor-acceptor-donor (D-A-D) structures, two new blue TADF emitters are designed by simply inserting a phenyl ring between D and A units. The TADF processes of the four thioxanthone derivatives are studied systematically through first-principles calculations. The role of the introduced phenyl ring in the excited state properties of the designed molecules is explored by analyzing the changes in molecular geometries, frontier molecular orbital distributions, the lowest singlet-triplet energy splitting (ΔEST), the spin orbit coupling (SOC) constants, the radiative decay rates (kr) and the nonradiative decay rates (knr), as well as the intersystem crossing rates (kISC) and reverse intersystem crossing rates (kRISC). The results show that when incorporating phenyl units into the D-A and D-A-D structures, both high kr and enhanced kRISC are achieved in Cz-Ph-SOXO and DCz-DPh-SOXO, demonstrating that incorporating the phenyl unit in D-A and D-A-D structures is an efficient way for developing new SOXO-based TADF molecules. It is worth noting that the kRISC values for Cz-Ph-SOXO and DCz-DPh-SOXO are significantly increased with respect to those of the experimental molecules. The present results would provide helpful guidelines for developing new SOXO-based TADF molecules experimentally.
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Affiliation(s)
- Lijuan Wang
- School of Materials Science and Engineering, Harbin Institute of Technology at Weihai, 2 West Wenhua Road, Weihai, 264209, China.
| | - Zhongqi Ge
- School of Materials Science and Engineering, Harbin Institute of Technology at Weihai, 2 West Wenhua Road, Weihai, 264209, China.
| | - Lin Xu
- School of Materials Science and Engineering, Harbin Institute of Technology at Weihai, 2 West Wenhua Road, Weihai, 264209, China.
| | - Yan Song
- School of Materials Science and Engineering, Harbin Institute of Technology at Weihai, 2 West Wenhua Road, Weihai, 264209, China.
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Wang Y, Tian Y, Gao Y, Guo Z, Xue Z, Han Y, Yang W, Ma X. Resolving the Photophysics of Nitrogen-Embedded Multiple Resonance Emitters: Origin of Color Purity and Emitting Efficiency. J Phys Chem Lett 2023; 14:9665-9676. [PMID: 37870971 DOI: 10.1021/acs.jpclett.3c02245] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2023]
Abstract
The emerging nitrogen-embedded multiple resonance (MR) emitters with an indolo[3,2,1-jk] carbazole (ICz) unit have exhibited promising performance for high-resolution organic light-emitting diode (OLED) devices, while the underlying photophysics has been rarely reported. In this work, the optical spectra, color purity, and emitting efficiency of ICz-based MR emitters were investigated by using electronic structure and thermal vibration correlation function (TVCF) calculations. Unlike B-N MR emitters, the high color purity of investigated ICz-based MR emitters was mainly contributed by considerable structural rigidity, which also greatly affects the radiative decay rate and fluorescence quantum yield of the S1 state. For the majority of investigated emitters, potential reverse intersystem crossing (RISC) channels (T1 → S1 and T2 → S1) are limited by thermally inaccessible ΔEST* or insufficient spin-orbital coupling (SOC), which can be distinguished by the calculated temperature-dependent RISC rate pattern. We provided a systematic photophysical picture for ICz-based MR emitters that might be interesting for the OLED design and application community.
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Affiliation(s)
- Yaxin Wang
- Institute of Molecular Plus, Tianjin University, Tianjin 300072, P. R. China
| | - Yiran Tian
- Institute of Molecular Plus, Tianjin University, Tianjin 300072, P. R. China
| | - Yixuan Gao
- Institute of Molecular Plus, Tianjin University, Tianjin 300072, P. R. China
| | - Zilong Guo
- Institute of Molecular Plus, Tianjin University, Tianjin 300072, P. R. China
| | - Zheng Xue
- Engineering Research Center for Nanomaterials, Henan University, Kaifeng 475004, P. R. China
| | - Yandong Han
- Engineering Research Center for Nanomaterials, Henan University, Kaifeng 475004, P. R. China
| | - Wensheng Yang
- Institute of Molecular Plus, Tianjin University, Tianjin 300072, P. R. China
- Engineering Research Center for Nanomaterials, Henan University, Kaifeng 475004, P. R. China
| | - Xiaonan Ma
- Institute of Molecular Plus, Tianjin University, Tianjin 300072, P. R. China
- Engineering Research Center for Nanomaterials, Henan University, Kaifeng 475004, P. R. China
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5
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Rohman S, Kar R. Understanding Photophysical Properties of Molecules Relevant in Organic Semiconductor Laser Diodes from Electron Localization Function-Tuned and Solvent-Tuned Range-Separated Functionals. J Phys Chem A 2023; 127:9069-9081. [PMID: 37862688 DOI: 10.1021/acs.jpca.3c05486] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2023]
Abstract
Organic semiconductor laser diodes (OSLDs) are prevalent in optoelectronics because of their sustainable energy applications. Organic molecules used in such diodes are usually large; hence, their studies are computationally challenging with high-end benchmark methods. Computational methods with reliable accuracy and efficiency are always indispensable. In the present work, we have applied our computationally inexpensive, nonempirically tuned [electron localization function (ELF*) and solvent (Sol*)] range-separated (RS) functionals to study five molecules used in OSLDs. The emission energies in three different environments [toluene, CBP (4,4'-bis(n-carbazolyl)-1,1'-biphenyl) film, and gas] have been computed with the tuned functionals and compared with the experimental emission energies. ELF* and Sol* functionals can accurately reproduce emission energies in toluene and CBP film environments. On the other hand, both ELF* and IP-tuned functionals with excited-state geometry (IP*) perform better in the gas phase. In addition, a comparative study is performed between time-dependent density functional theory and the Tamm-Dancoff approximation. Along with the emission energy, oscillator strength values have also been reported. Different IP-tuned RS parameters were obtained with the ground- and excited-state geometries. Interestingly, it has been observed that the optimally tuned RS parameter with excited-state geometry (IP*) performs better compared to that with ground-state geometries (IP). Fractional occupation calculations show that the tuned functionals exhibit less localization and delocalization error. The study envisages that ELF* and Sol* functionals can be used to design future candidates for OSLDs.
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Affiliation(s)
- Satter Rohman
- Department of Chemistry, Dibrugarh University, Dibrugarh, Assam 786004, India
| | - Rahul Kar
- Department of Chemistry, Dibrugarh University, Dibrugarh, Assam 786004, India
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6
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Wang X, Wang S, Wang J, Yin S. Reverse Designing the Wavelength-Specific Thermally Activation Delayed Fluorescent Molecules Using a Genetic Algorithm Coupled with Cheap QM Methods. J Phys Chem A 2023. [PMID: 37418642 DOI: 10.1021/acs.jpca.3c01714] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/09/2023]
Abstract
Genetic algorithm (GA) optimization coupled with the semiempirical intermediate neglect of differential overlap (INDO)/CIS method is presented to inversely design the red thermally activation delayed fluorescent (TADF) molecules. According to the predefined donor-acceptor (DA) library to build an ADn-type TADF candidate, we utilized the chemical notation language SMILES code to generate a TADF molecule and apply the RDKit program to produce the initial 3D molecular structure. A combined fitness function is proposed to evaluate the performance of the functional-lead TADF molecule. The fitness function includes three key parameters, i.e., the emission wavelength, the energy gap (ΔEST) between the lowest singlet (S1)- and triplet (T1)-excited states, and the oscillator strengths for electron transition from S0 and S1. A cheap QM method, i.e., INDO/CIS, on the basis of an xTB-optimized molecular geometry is applied to quickly calculate the fitness function. Finally, the GA approach is utilized to globally search for the wavelength-specific TADF molecules under our predefined DA library, and the optimum 630 nm red and 660 nm deep red TADF molecules are inversely designed according to the evolution of molecular fitness functions.
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Affiliation(s)
- Xubin Wang
- School of Chemistry & Chemical Engineering, Shaanxi Normal University, Xian 710119, China
| | - Shiqi Wang
- School of Chemistry & Chemical Engineering, Shaanxi Normal University, Xian 710119, China
| | - Jingwen Wang
- School of Chemistry & Chemical Engineering, Shaanxi Normal University, Xian 710119, China
| | - Shiwei Yin
- School of Chemistry & Chemical Engineering, Shaanxi Normal University, Xian 710119, China
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7
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Dong H, Feng Y, Bu Y. Electron Presolvation in Tetrahydrofuran-Incorporated Supramolecular Sodium Entities. J Phys Chem A 2023; 127:1402-1412. [PMID: 36748233 DOI: 10.1021/acs.jpca.2c06944] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Alkali metal atoms can repopulate their valence electrons toward solvation due to impact from solvents or microsurroundings and provide the remaining alkali metal cations for coordinating with a variety of specific solvents, forming various electron-expanded complexes or solvated ionic pairs with special interactions. Such special solute-solvent interactions not only affect their electronic structures but also enable the formation of entirely new species. Taking Na(THF)n (n = 1-6, THF = tetrahydrofuran) and Na2@THF complexes as typical representatives, density functional theory calculations are carried out to explore the solvation of a sodium atom and its dimer in THF and characterize their complexes as solvent-incorporated supramolecular entities and particularly valence electron presolvation due to their interaction with solvent THF. Electron presolvation is caused by the Pauli repulsion between THF containing a coordinating O atom with a lone pair of electrons and the alkali metal Na or Na2 containing valence electrons, and THF coordination to them forces their valence electrons to redistribute, which can be easily realized in such solvents. Compared with strongly bound valance electrons of alkali metal atoms, THF coordination enables Na or Na2 electrons to exhibit much more active states (i.e., the presolvated states) featuring small vertical detachment energies of electrons and distorted diffuse distributions in the frames of the generally structured metal cation complexes, acting as the electron-expanded chemical entities. Furthermore, the degree of electron diffusion and the polarity of the Na-Na bond are proportional to the coordination number (n) and the coordination number difference (Δn) between two Na centers in Na2@THF. The unique properties of such entities are also discussed. This work offers a theoretical support to the supramolecular entities formed by alkali-metal atoms or their dimers with ligands containing O or N and uncovers the unique electron presolvation phenomena and also enriches our understanding of the novel metal atom complexes.
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Affiliation(s)
- Hui Dong
- School of Chemistry and Chemical Engineering, Shandong University, Jinan250100, P. R. China
| | - Yiwei Feng
- School of Chemistry and Chemical Engineering, Shandong University, Jinan250100, P. R. China
| | - Yuxiang Bu
- School of Chemistry and Chemical Engineering, Shandong University, Jinan250100, P. R. China
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8
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Mandal B, Dunietz BD. Effects of Solvent Dielectric on Thermally Activated Delayed Fluorescence: A Predictive Computational Polarization Consistent Approach. J Phys Chem A 2023; 127:216-223. [PMID: 36563166 DOI: 10.1021/acs.jpca.2c08154] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
We study computationally thermally activated delayed fluorescence (TADF) in donor-acceptor compounds. The relevant electronic excited states that are strongly affected by the dielectric environment are treated by a polarization consistent framework. The high fidelity potential energy surfaces are used following a quantum-mechanical Fermi's golden rule (FGR) picture to calculate rates of intersystem crossing (ISC) and reverse intersystem crossing (RISC). To demonstrate the potency of the approach, we consider isomers of benzonitrile functionalized tert-butyl-substituted dimethylacridine (DMAC-BN), which were recently found to perform well as TADF emitters. The calculated excited state energies that appear to reproduce well measured spectral trends with respect to the dielectric constant are used to parametrize ISC/RISC FGR rates. The calculated rates reproduce well measured rates, whereas semiclassical based rates are grossly underestimated. In particular, we find in agreement with the recent experimental study [Phys. Rev. Appl.2019, 12, 044021] that the ortho and meta isomers are significantly more effective as TADF emitters. The computational framework provides valuable insight at the molecular level into RISC rates and therefore can contribute to the design of materials of increased TADF efficiency.
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Affiliation(s)
- Bikash Mandal
- Department of Chemistry and Biochemistry, Kent State University, Kent, Ohio44242-0001, United States
| | - Barry D Dunietz
- Department of Chemistry and Biochemistry, Kent State University, Kent, Ohio44242-0001, United States
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9
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Froitzheim T, Grimme S, Mewes JM. Either Accurate Singlet-Triplet Gaps or Excited-State Structures: Testing and Understanding the Performance of TD-DFT for TADF Emitters. J Chem Theory Comput 2022; 18:7702-7713. [PMID: 36409831 DOI: 10.1021/acs.jctc.2c00905] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The energy gap between the lowest singlet and triplet excited states (ΔEST) is a key property of thermally activated delayed fluorescence (TADF) emitters, where these states are dominated by charge-transfer (CT) character. Despite its well-known shortcomings concerning CT states, time-dependent density functional theory (TD-DFT) is widely used to predict this gap and study TADF. Moreover, polar CT states exhibit a strong interaction with their molecular environment, which further complicates their computational description. Addressing these two major challenges, this work studies the performance of Tamm-Dancoff-approximated TD-DFT (TDA-DFT) on the recent STGABS27 benchmark set,1 exploring different strategies to include orbital and structural relaxation, as well as dielectric embedding. The results show that the best-performing strategy is to calculate ΔEST at the ground-state structure using functionals with a surprisingly small amount of Fock exchange of ≈10% and without a (complete) solvent model. However, as this approach heavily relies on error cancellation to mimic dielectric relaxation, it is not robust and exhibits large systematic deviations in excited state energies, state characters, and structures. More rigorous approaches, including state-specific solvation, do not share these systematic deviations, but their predicted ΔEST values exhibit larger statistical errors. We thus conclude that for the description of CT states in dielectric environments, none of the tested TDA-DFT methods is competitive with the recently presented ROKS/PCM approach regarding robustness, accuracy, and computational efficiency.
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Affiliation(s)
- Thomas Froitzheim
- Mulliken Center for Theoretical Chemistry, University of Bonn, Beringstr. 4, 53115Bonn, Germany
| | - Stefan Grimme
- Mulliken Center for Theoretical Chemistry, University of Bonn, Beringstr. 4, 53115Bonn, Germany
| | - Jan-Michael Mewes
- Mulliken Center for Theoretical Chemistry, University of Bonn, Beringstr. 4, 53115Bonn, Germany
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10
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Ye JT, Chen XY, Qiu YQ. First Hyperpolarizabilities of Intramolecular Charge-Transfer Architectures Based on Acenaphthene Derivatives in Gas, Solution, and Solid States. J Phys Chem A 2022; 126:7432-7441. [PMID: 36218337 DOI: 10.1021/acs.jpca.2c04380] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Constructing charge transfer (CT) systems and packing arrangement are common and effective methods to control the efficiency of nonlinear optical (NLO) materials. Apart from the traditional through-bond CT (TBCT) systems, through-space CT (TSCT) also leads to distinctive optical and electronic properties. Meanwhile, corresponding theoretical investigations of the aggregation effect are highly desired. In this work, some TSCT and model compounds incorporating acenaphthene as a scaffold and triphenylamine (TPA) as the donor are theoretically performed to systematically reveal the effect of both solvent and solid environments on their static first hyperpolarizabilities (βtot) by using the polarizable continuum model (PCM) and the combined quantum mechanics and molecular mechanics (QM/MM) method. Results indicate that the dichloromethane solvent effect within the PCM approach causes an almost 2 times increase of the βtot values. Besides, the different packing modes and intermolecular interactions have remarkable influence on the second-order NLO properties. For the case of TPA-ace-CN in the crystal state, the parallel arrangement will lead to large NLO responses (4.9 × 10-30 esu) compared to the correspondingly isolated molecule (3.4 × 10-30 esu). However, for the TPA-ace-TRZ compound with the TSCT architecture, selection of the molecular arrangement may make the aggregate ineffective due to the offset of the through-space dipole and charge transfer between D-A groups, which lead to the βtot values decreasing from 15.2 × 10-30 to 7.7 × 10-30 esu. We believe that our calculation will serve as a guide for the exploration of more efficient NLO materials wherein the molecules are oriented in their most favorable arrangements.
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Affiliation(s)
- Jin-Ting Ye
- College of Chemistry and Materials Science, Inner Mongolia Minzu University, Tongliao028000, China
| | - Xing-Yi Chen
- College of Chemistry and Materials Science, Inner Mongolia Minzu University, Tongliao028000, China
| | - Yong-Qing Qiu
- Institute of Functional Material Chemistry, Faculty of Chemistry, Northeast Normal University, Changchun130024, China
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11
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de Sousa LE, de Silva P. Diabatic Decomposition Perspective on the Role of Charge Transfer and Local Excitations in Thermally Activated Delayed Fluorescence. J Chem Theory Comput 2022; 18:5459-5470. [PMID: 36007256 DOI: 10.1021/acs.jctc.2c00310] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Thermally activated delayed fluorescence (TADF) is a phenomenon that relies on the upconversion of triplet excitons to singlet excitons by means of reverse intersystem crossing (rISC). It has been shown both experimentally and theoretically that the TADF mechanism depends on the interplay between charge transfer and local excitations. However, the difference between the diabatic and adiabatic character of the involved excited states is rarely discussed in the literature. Here we develop a diabatization procedure to implement a four-state model Hamiltonian to a set of TADF molecules. We provide physical interpretations of the Hamiltonian elements and show their dependence on the electronic state of the equilibrium geometry. We also demonstrate how vibrations affect the TADF efficiency by modifying the diabatic decomposition of the molecule. Finally, we provide a simple model that connects the diabatic Hamiltonian to the electronic properties relevant to TADF and show how this relationship translates into different optimization strategies for rISC, fluorescence, and overall TADF performance.
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Affiliation(s)
- Leonardo Evaristo de Sousa
- Department of Energy Conversion and Storage, Technical University of Denmark, Anker Engelunds Vej 301, 2800 Kongens Lyngby, Denmark
| | - Piotr de Silva
- Department of Energy Conversion and Storage, Technical University of Denmark, Anker Engelunds Vej 301, 2800 Kongens Lyngby, Denmark
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12
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Wang Y, Guo Z, Gao Y, Tian Y, Deng Y, Ma X, Yang W. Tuning Hybridized Local and Charge-Transfer Mixing for Efficient Hot-Exciton Emission with Improved Color Purity. J Phys Chem Lett 2022; 13:6664-6673. [PMID: 35839081 DOI: 10.1021/acs.jpclett.2c01917] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Delayed fluorescence (DF) emitters with high color purity are of high interest for applications in high-resolution displays. However, the charge transfer required by high emitting efficiency usually conflicts with the expected color purity. In this work, we investigated the S1/S0 conformational relaxation, spin-orbital coupling (SOC), and vibronic coupling of hot-exciton emitters while hybrid local and charge transfer (HLCT) state tuning was achieved by a structural meta-effect. The meta-linkage leads to suppressed S1/S0 conformational relaxation and weakened vibronic coupling, while the unsacrificed emitting efficiency is largely ensured by multiple rISC channels (Tn → Sm) with thermally accessible triplet-singlet energy gap (ΔEST) and effective SOC. We demonstrated that the unique excited-state mechanism provides opportunities to improve the emitting color purity of hot-exciton emitters without sacrificing emitting efficiency by HLCT state tuning with simple chemical structural modification, for which hot-exciton emitters might play a more important role for high-resolution organic light-emitting diode displays.
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Affiliation(s)
- Yaxin Wang
- Institute of Molecular Plus, Tianjin University, Tianjin 300072, P.R. China
| | - Zilong Guo
- Institute of Molecular Plus, Tianjin University, Tianjin 300072, P.R. China
| | - Yixuan Gao
- Institute of Molecular Plus, Tianjin University, Tianjin 300072, P.R. China
| | - Yiran Tian
- Institute of Molecular Plus, Tianjin University, Tianjin 300072, P.R. China
| | - Yingyi Deng
- Institute of Molecular Plus, Tianjin University, Tianjin 300072, P.R. China
| | - Xiaonan Ma
- Institute of Molecular Plus, Tianjin University, Tianjin 300072, P.R. China
| | - Wensheng Yang
- Institute of Molecular Plus, Tianjin University, Tianjin 300072, P.R. China
- Engineering Research Center for Nanomaterials, Henan University, Kaifeng 475004, P.R. China
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13
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Francese T, Kundu A, Gygi F, Galli G. Quantum simulations of thermally activated delayed fluorescence in an all-organic emitter. Phys Chem Chem Phys 2022; 24:10101-10113. [PMID: 35416814 DOI: 10.1039/d2cp01147f] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We investigate the prototypical NAI-DMAC thermally activated delayed fluorescence (TADF) emitter in the gas phase- and high-packing fraction limits at finite temperature, by combining first principles molecular dynamics with a quantum thermostat to account for nuclear quantum effects (NQE). We find a weak dependence of the singlet-triplet energy gap (ΔEST) on temperature in both the solid and the molecule, and a substantial effect of packing. While the ΔEST vanishes in the perfect crystal, it is of the order of ∼0.3 eV in the molecule, with fluctuations ranging from 0.1 to 0.4 eV at 300 K. The transition probability between the HOMOs and LUMOs has a stronger dependence on temperature than the singlet-triplet gap, with a desirable effect for thermally activated fluorescence; such temperature effect is weaker in the condensed phase than in the molecule. Our results on ΔEST and oscillator strengths, together with our estimates of direct and reverse intersystem crossing rates, show that optimization of packing and geometrical conformation is critical to increase the efficiency of TADF compounds. Our findings highlight the importance of considering thermal fluctuations and NQE to obtain robust predictions of the electronic properties of NAI-DMAC.
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Affiliation(s)
- Tommaso Francese
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL 60637, USA.
| | - Arpan Kundu
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL 60637, USA.
| | - Francois Gygi
- Department of Computer Science, University of California, Davis, CA 95616, 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
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14
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Spin Orbit Coupling in Orthogonal Charge Transfer States: (TD-)DFT of Pyrene-Dimethylaniline. Molecules 2022; 27:molecules27030891. [PMID: 35164162 PMCID: PMC8839636 DOI: 10.3390/molecules27030891] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2021] [Revised: 01/25/2022] [Accepted: 01/26/2022] [Indexed: 11/17/2022] Open
Abstract
The conformational dependence of the matrix element for spin-orbit coupling and of the electronic coupling for charge separation are determined for an electron donor-acceptor system containing a pyrene acceptor and a dimethylaniline donor. Different kinetic and energetic aspects that play a role in the spin-orbit charge transfer intersystem crossing (SOCT-ISC) mechanism are discussed. This includes parameters related to initial charge separation and the charge recombination pathways using the Classical Marcus Theory of electron transfer. The spin-orbit coupling, which plays a significant role in charge recombination to the triplet state, can be probed by (TD)-DFT, using the latter as a tool to understand and predict the SOCT-ISC mechanism. The matrix elements for spin-orbit coupling for acetone and 4-thio-thymine are used for benchmarking. (Time Dependent-) Density Functional Theory (DFT and TD-DFT) calculations are applied using the quantum chemical program Amsterdam Density Functional (ADF).
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15
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Lin KH, Wetzelaer GJAH, Blom PWM, Andrienko D. Virtual Screening of TADF Emitters for Single-Layer OLEDs. Front Chem 2022; 9:800027. [PMID: 34976956 PMCID: PMC8716429 DOI: 10.3389/fchem.2021.800027] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2021] [Accepted: 11/17/2021] [Indexed: 11/13/2022] Open
Abstract
Thermally-activated delayed fluorescence (TADF) is a concept which helps to harvest triplet excitations, boosting the efficiency of an organic light-emitting diode. TADF can be observed in molecules with spatially separated donor and acceptor groups with a reduced triplet-singlet energy level splitting. TADF materials with balanced electron and hole transport are attractive for realizing efficient single-layer organic light emitting diodes, greatly simplifying their manufacturing and improving their stability. Our goal here is to computationally screen such materials and provide a comprehensive database of compounds with a range of emission wavelengths, ionization energies, and electron affinities.
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Affiliation(s)
- Kun-Han Lin
- Max Planck Institute for Polymer Research, Mainz, Germany
| | | | - Paul W M Blom
- Max Planck Institute for Polymer Research, Mainz, Germany
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16
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Li J, Li T, Zhang M, Guo D, Zhang H. Rational designs of structurally similar TADF and HLCT emitters with benzo- or naphtho-carbazole units as electron donors. Phys Chem Chem Phys 2022; 24:25937-25949. [DOI: 10.1039/d2cp03500f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Structurally similar D–A type molecules with the combination of benzo- or naphtho-carbazole units as electron donors and tunable electron acceptors with different electron-withdrawing ability are designed to realize HLCT and TADF emissions.
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Affiliation(s)
- Jiaqi Li
- State Key Laboratory of Supramolecular Structure and Materials, Institute of Theoretical Chemistry, College of Chemistry, Jilin University, Changchun 130012, P. R. China
| | - Tingyu Li
- State Key Laboratory of Supramolecular Structure and Materials, Institute of Theoretical Chemistry, College of Chemistry, Jilin University, Changchun 130012, P. R. China
| | - Mingfan Zhang
- State Key Laboratory of Supramolecular Structure and Materials, Institute of Theoretical Chemistry, College of Chemistry, Jilin University, Changchun 130012, P. R. China
| | - Dongxue Guo
- State Key Laboratory of Supramolecular Structure and Materials, Institute of Theoretical Chemistry, College of Chemistry, Jilin University, Changchun 130012, P. R. China
| | - Houyu Zhang
- State Key Laboratory of Supramolecular Structure and Materials, Institute of Theoretical Chemistry, College of Chemistry, Jilin University, Changchun 130012, P. R. China
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17
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Guo Y, Guan H, Li P, Wang C, Wu Z, Wang Y, Yu Z, Zhang Z, Wang S, Zhao G. Thermally Activated Delayed Fluorescence Enabled by Reversed Conformational Distortion for Blue Emitters. J Phys Chem Lett 2021; 12:9501-9507. [PMID: 34559539 DOI: 10.1021/acs.jpclett.1c02642] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
In this work, we present for the first time a general strategy via molecular reversed conformational distortion for thermally activated delayed fluorescence (TADF). A model purely organic compound named BNNIO with a common fluorophore flexibly linked to benzene by an oxygen atom is rationally designed and successfully synthesized. Moreover, the rate constant of reverse intersystem crossing reaches 2.34 × 104 s-1 as determined by transient spectroscopy. As a result, TADF emission of BNNIO is observed with a photoluminescence quantum yield of 90.72% and a lifetime of 84.76 μs at 415 nm. This universal regulation strategy undoubtedly opens a new avenue for the development of novel purely organic blue light-emitting materials.
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Affiliation(s)
- Yurong Guo
- Department of Chemistry, Molecular Dynamic Chemistry Center, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, School of Science, Tianjin University, Tianjin 300354, China
| | - Hongwei Guan
- Institute of Molecular Sciences and Engineering, Shandong University, Qingdao 266237, China
| | - Peng Li
- Institute of Molecular Sciences and Engineering, Shandong University, Qingdao 266237, China
| | - Chao Wang
- Department of Chemistry, Molecular Dynamic Chemistry Center, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, School of Science, Tianjin University, Tianjin 300354, China
| | - Zibo Wu
- Department of Chemistry, Molecular Dynamic Chemistry Center, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, School of Science, Tianjin University, Tianjin 300354, China
| | - Yanan Wang
- Department of Chemistry, Molecular Dynamic Chemistry Center, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, School of Science, Tianjin University, Tianjin 300354, China
| | - Zhenyi Yu
- Department of Chemistry, Molecular Dynamic Chemistry Center, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, School of Science, Tianjin University, Tianjin 300354, China
| | - Zhen Zhang
- Department of Chemistry, Molecular Dynamic Chemistry Center, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, School of Science, Tianjin University, Tianjin 300354, China
| | - Shiping Wang
- Department of Chemistry, Molecular Dynamic Chemistry Center, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, School of Science, Tianjin University, Tianjin 300354, China
| | - Guangjiu Zhao
- Department of Chemistry, Molecular Dynamic Chemistry Center, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, School of Science, Tianjin University, Tianjin 300354, China
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18
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Ortstein K, Hutsch S, Hambsch M, Tvingstedt K, Wegner B, Benduhn J, Kublitski J, Schwarze M, Schellhammer S, Talnack F, Vogt A, Bäuerle P, Koch N, Mannsfeld SCB, Kleemann H, Ortmann F, Leo K. Band gap engineering in blended organic semiconductor films based on dielectric interactions. NATURE MATERIALS 2021; 20:1407-1413. [PMID: 34112978 DOI: 10.1038/s41563-021-01025-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2020] [Accepted: 04/26/2021] [Indexed: 06/12/2023]
Abstract
Blending organic molecules to tune their energy levels is currently being investigated as an approach to engineer the bulk and interfacial optoelectronic properties of organic semiconductors. It has been proven that the ionization energy and electron affinity can be equally shifted in the same direction by electrostatic effects controlled by blending similar halogenated derivatives with different energetics. Here we show that the energy gap of organic semiconductors can also be tuned by blending. We use oligothiophenes with different numbers of thiophene rings as an example and investigate their structure and electronic properties. Photoelectron spectroscopy and inverse photoelectron spectroscopy show tunability of the single-particle gap, with the optical gaps showing similar, but smaller, effects. Theoretical analysis shows that this tuning is mainly caused by a change in the dielectric constant with blend ratio. Further studies will explore the practical impact of this energy-level engineering strategy for optoelectronic devices.
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Affiliation(s)
- Katrin Ortstein
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universität Dresden, Dresden, Germany
| | - Sebastian Hutsch
- Center for Advancing Electronics Dresden, Technische Universität Dresden, Dresden, Germany
- Technische Universität München, Department of Chemistry, Garching, Germany
| | - Mike Hambsch
- Center for Advancing Electronics Dresden, Technische Universität Dresden, Dresden, Germany
- Faculty of Electrical and Computer Engineering, Technische Universität Dresden, Dresden, Germany
| | - Kristofer Tvingstedt
- Lehrstuhl für Experimentelle Physik IV, Julius-Maximilians-Universität Würzburg, Würzburg, Germany
| | - Berthold Wegner
- Institut für Physik & IRIS Adlershof, Humboldt-Universität zu Berlin, Berlin, Germany
| | - Johannes Benduhn
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universität Dresden, Dresden, Germany
| | - Jonas Kublitski
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universität Dresden, Dresden, Germany
| | - Martin Schwarze
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universität Dresden, Dresden, Germany
| | - Sebastian Schellhammer
- Center for Advancing Electronics Dresden, Technische Universität Dresden, Dresden, Germany
| | - Felix Talnack
- Center for Advancing Electronics Dresden, Technische Universität Dresden, Dresden, Germany
- Faculty of Electrical and Computer Engineering, Technische Universität Dresden, Dresden, Germany
| | - Astrid Vogt
- Institut für Organische Chemie II und Neue Materialien, Universität Ulm, Ulm, Germany
| | - Peter Bäuerle
- Institut für Organische Chemie II und Neue Materialien, Universität Ulm, Ulm, Germany
| | - Norbert Koch
- Institut für Physik & IRIS Adlershof, Humboldt-Universität zu Berlin, Berlin, Germany
| | - Stefan C B Mannsfeld
- Center for Advancing Electronics Dresden, Technische Universität Dresden, Dresden, Germany
- Faculty of Electrical and Computer Engineering, Technische Universität Dresden, Dresden, Germany
| | - Hans Kleemann
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universität Dresden, Dresden, Germany
| | - Frank Ortmann
- Center for Advancing Electronics Dresden, Technische Universität Dresden, Dresden, Germany.
- Technische Universität München, Department of Chemistry, Garching, Germany.
| | - Karl Leo
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universität Dresden, Dresden, Germany.
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19
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Kunze L, Hansen A, Grimme S, Mewes JM. PCM-ROKS for the Description of Charge-Transfer States in Solution: Singlet-Triplet Gaps with Chemical Accuracy from Open-Shell Kohn-Sham Reaction-Field Calculations. J Phys Chem Lett 2021; 12:8470-8480. [PMID: 34449230 DOI: 10.1021/acs.jpclett.1c02299] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
The adiabatic energy gap between the lowest singlet and triplet excited states ΔEST is a central property of thermally activated delayed fluorescence (TADF) emitters. Since these states are dominated by a charge-transfer character, causing strong orbital-relaxation and environmental effects, an accurate prediction of ΔEST is very challenging, even with modern quantum-chemical excited-state methods. Addressing this major challenge, we present an approach that combines spin-unrestricted (UKS) and restricted open-shell Kohn-Sham (ROKS) self-consistent field calculations with a polarizable-continuum model and range-separated hybrid functionals. Tests on a new representative benchmark set of 27 TADF emitters with accurately known ΔEST values termed STGABS27 reveal a robust and unprecedented performance with a mean absolute deviation of only 0.025 eV (∼0.5 kcal/mol) and few deviations greater than 0.05 eV (∼1 kcal/mol), even in electronically challenging cases. Requiring only two geometry optimizations per molecule at the ROKS/UKS level in a compact double-ζ basis, the approach is computationally efficient and can routinely be applied to molecules with more than 100 atoms.
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Affiliation(s)
- Lukas Kunze
- Mulliken Center for Theoretical Chemistry, Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms Universität Bonn, Beringstraßze 4, 53115 Bonn, Germany
| | - Andreas Hansen
- Mulliken Center for Theoretical Chemistry, Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms Universität Bonn, Beringstraßze 4, 53115 Bonn, Germany
| | - Stefan Grimme
- Mulliken Center for Theoretical Chemistry, Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms Universität Bonn, Beringstraßze 4, 53115 Bonn, Germany
| | - Jan-Michael Mewes
- Mulliken Center for Theoretical Chemistry, Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms Universität Bonn, Beringstraßze 4, 53115 Bonn, Germany
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20
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de Sousa LE, de Silva P. Unified Framework for Photophysical Rate Calculations in TADF Molecules. J Chem Theory Comput 2021; 17:5816-5824. [PMID: 34383498 DOI: 10.1021/acs.jctc.1c00476] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
One of the challenges in organic light-emitting diodes research is finding ways to increase device efficiency by making use of the triplet excitons that are inevitably generated in the process of electroluminescence. One way to do so is by thermally activated delayed fluorescence (TADF), a process in which triplet excitons undergo upconversion to singlet states, allowing them to relax radiatively. The discovery of this phenomenon has ensued a quest for new materials that are able to effectively take advantage of this mechanism. From a theoretical standpoint, this requires the capacity to estimate the rates of the various processes involved in the photophysics of candidate molecules, such as intersystem crossing, reverse intersystem crossing, fluorescence, and phosphorescence. Here, we present a method that is able to, within a single framework, compute all of these rates and predict the photophysics of new molecules. We apply the method to two TADF molecules and show that results compare favorably with other theoretical approaches and experimental results. Finally, we use a kinetic model to show how the calculated rates act in concert to produce different photophysical behavior.
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Affiliation(s)
- Leonardo Evaristo de Sousa
- Department of Energy Conversion and Storage, Technical University of Denmark, Anker Engelunds Vej 301, 2800 Kongens Lyngby, Denmark
| | - Piotr de Silva
- Department of Energy Conversion and Storage, Technical University of Denmark, Anker Engelunds Vej 301, 2800 Kongens Lyngby, Denmark
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21
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Yang L, Horton JT, Payne MC, Penfold TJ, Cole DJ. Modeling Molecular Emitters in Organic Light-Emitting Diodes with the Quantum Mechanical Bespoke Force Field. J Chem Theory Comput 2021; 17:5021-5033. [PMID: 34264669 DOI: 10.1021/acs.jctc.1c00135] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Combined molecular dynamics (MD) and quantum mechanics (QM) simulation procedures have gained popularity in modeling the spectral properties of functional organic molecules. However, the potential energy surfaces used to propagate long-time scale dynamics in these simulations are typically described using general, transferable force fields designed for organic molecules in their electronic ground states. These force fields do not typically include spectroscopic data in their training, and importantly, there is no general protocol for including changes in geometry or intermolecular interactions with the environment that may occur upon electronic excitation. In this work, we show that parameters tailored for thermally activated delayed fluorescence (TADF) emitters used in organic light-emitting diodes (OLEDs), in both their ground and electronically excited states, can be readily derived from a small number of QM calculations using the QUBEKit (QUantum mechanical BEspoke toolKit) software and improve the overall accuracy of these simulations.
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Affiliation(s)
- Lupeng Yang
- TCM Group, Cavendish Laboratory, 19 JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Joshua T Horton
- School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom
| | - Michael C Payne
- TCM Group, Cavendish Laboratory, 19 JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Thomas J Penfold
- School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom
| | - Daniel J Cole
- School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom
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22
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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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23
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Dhali R, Phan Huu DKA, Bertocchi F, Sissa C, Terenziani F, Painelli A. Understanding TADF: a joint experimental and theoretical study of DMAC-TRZ. Phys Chem Chem Phys 2021; 23:378-387. [DOI: 10.1039/d0cp05982j] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
TADF offers a promising way to harvest triplets in OLED for improved efficiency. To concurrently optimize the dye inside the matrix, a thorough experimental and theoretical study is presented of a the TADF dye addressing environmental effects.
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Affiliation(s)
- Rama Dhali
- Department of Chemistry
- Life Science and Environmental Sustainability
- University of Parma
- 43124 Parma
- Italy
| | - D. K. Andrea Phan Huu
- Department of Chemistry
- Life Science and Environmental Sustainability
- University of Parma
- 43124 Parma
- Italy
| | - Francesco Bertocchi
- Department of Chemistry
- Life Science and Environmental Sustainability
- University of Parma
- 43124 Parma
- Italy
| | - Cristina Sissa
- Department of Chemistry
- Life Science and Environmental Sustainability
- University of Parma
- 43124 Parma
- Italy
| | - Francesca Terenziani
- Department of Chemistry
- Life Science and Environmental Sustainability
- University of Parma
- 43124 Parma
- Italy
| | - Anna Painelli
- Department of Chemistry
- Life Science and Environmental Sustainability
- University of Parma
- 43124 Parma
- Italy
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24
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Tang X, Cui LS, Li HC, Gillett AJ, Auras F, Qu YK, Zhong C, Jones STE, Jiang ZQ, Friend RH, Liao LS. Highly efficient luminescence from space-confined charge-transfer emitters. NATURE MATERIALS 2020; 19:1332-1338. [PMID: 32541938 DOI: 10.1038/s41563-020-0710-z] [Citation(s) in RCA: 226] [Impact Index Per Article: 56.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/29/2019] [Accepted: 05/15/2020] [Indexed: 06/11/2023]
Abstract
Charge-transfer (CT) complexes, formed by electron transfer from a donor to an acceptor, play a crucial role in organic semiconductors. Excited-state CT complexes, termed exciplexes, harness both singlet and triplet excitons for light emission, and are thus useful for organic light-emitting diodes (OLEDs). However, present exciplex emitters often suffer from low photoluminescence quantum efficiencies (PLQEs), due to limited control over the relative orientation, electronic coupling and non-radiative recombination channels of the donor and acceptor subunits. Here, we use a rigid linker to control the spacing and relative orientation of the donor and acceptor subunits, as demonstrated with a series of intramolecular exciplex emitters based on 10-phenyl-9,10-dihydroacridine and 2,4,6-triphenyl-1,3,5-triazine. Sky-blue OLEDs employing one of these emitters achieve an external quantum efficiency (EQE) of 27.4% at 67 cd m-2 with only minor efficiency roll-off (EQE = 24.4%) at a higher luminous intensity of 1,000 cd m-2. As a control experiment, devices using chemically and structurally related but less rigid emitters reach substantially lower EQEs. These design rules are transferrable to other donor/acceptor combinations, which will allow further tuning of emission colour and other key optoelectronic properties.
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Affiliation(s)
- Xun Tang
- Institute of Functional Nano and Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Joint International Research Laboratory of Carbon-Based Functional Materials and Devices, Soochow University, Suzhou, China
| | - Lin-Song Cui
- Cavendish Laboratory, University of Cambridge, Cambridge, UK.
| | - Hong-Cheng Li
- Institute of Functional Nano and Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Joint International Research Laboratory of Carbon-Based Functional Materials and Devices, Soochow University, Suzhou, China
| | | | - Florian Auras
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | - Yang-Kun Qu
- Institute of Functional Nano and Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Joint International Research Laboratory of Carbon-Based Functional Materials and Devices, Soochow University, Suzhou, China
| | - Cheng Zhong
- Department of Chemistry, Hubei Key Laboratory on Organic and Polymeric Optoelectronic Materials, Wuhan University, Wuhan, China
| | - Saul T E Jones
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | - Zuo-Quan Jiang
- Institute of Functional Nano and Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Joint International Research Laboratory of Carbon-Based Functional Materials and Devices, Soochow University, Suzhou, China.
| | | | - Liang-Sheng Liao
- Institute of Functional Nano and Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Joint International Research Laboratory of Carbon-Based Functional Materials and Devices, Soochow University, Suzhou, China.
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25
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Zhang Y, Zhang K, Ma Y, Lin L, Wang CK, Fan J. Tunable lifetimes and efficiencies of room temperature phosphorescent liquids by modulating the length and number of alkyl chains. Phys Chem Chem Phys 2020; 22:19746-19757. [PMID: 32842141 DOI: 10.1039/d0cp03401k] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Organic room temperature phosphorescence (RTP) liquid composites exhibit the potential to make innovative changes in large area flexible lighting applications, and it is extremely challenging to achieve high-efficiency RTP in pure organic solvent-free liquid systems. The excited state properties and inner lighting mechanisms of these composites are unclear; therefore, a theoretical perspective to design high efficiency RTP liquids with tunable lifetime is highly desired. Herein, we systematically investigate the photophysical properties of a series of long swallow-tailed bromonaphthalimide (BT unit) molecules by the newly proposed optimally tuned range-separated (RS) functional method, and a state-of-the-art RTP molecule with an absolute quantum yield (ΦRTP) of 57.1% and a lifetime (τ) of 160 ms in solvent-free liquid is obtained. Moreover, theoretical results show that the energy gap between the lowest singlet excited state (S1) and triplet excited state (T1) can be reduced and the non-radiative energy consumption process can be restricted by modulating the length and number of alkyl chains in organic RTP molecules. Thus, a wise molecular design strategy is proposed and five additional efficient RTP molecules with tunable lifetimes (43, 19, 136, 0.11 and 0.005 ms) and efficiencies (11.3%, 6.8%, 5.9%, 0.2% and 0.05%) are theoretically proposed. This study sheds light on the relationship among molecular structure, lifetime and efficiency, and can provide an important prototype to explore high-efficiency RTP by pure organic solvent-free liquid systems.
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Affiliation(s)
- Yuchen Zhang
- Shandong Province Key Laboratory of Medical Physics and Image Processing Technology, Institute of Materials and Clean Energy, School of Physics and Electronics, Shandong Normal University, 250014 Jinan, China.
| | - Kai Zhang
- Shandong Province Key Laboratory of Medical Physics and Image Processing Technology, Institute of Materials and Clean Energy, School of Physics and Electronics, Shandong Normal University, 250014 Jinan, China.
| | - Yuying Ma
- Shandong Province Key Laboratory of Medical Physics and Image Processing Technology, Institute of Materials and Clean Energy, School of Physics and Electronics, Shandong Normal University, 250014 Jinan, China.
| | - Lili Lin
- Shandong Province Key Laboratory of Medical Physics and Image Processing Technology, Institute of Materials and Clean Energy, School of Physics and Electronics, Shandong Normal University, 250014 Jinan, China.
| | - Chuan-Kui Wang
- Shandong Province Key Laboratory of Medical Physics and Image Processing Technology, Institute of Materials and Clean Energy, School of Physics and Electronics, Shandong Normal University, 250014 Jinan, China.
| | - Jianzhong Fan
- Shandong Province Key Laboratory of Medical Physics and Image Processing Technology, Institute of Materials and Clean Energy, School of Physics and Electronics, Shandong Normal University, 250014 Jinan, China. and Guangdong Provincial Key Laboratory of Luminescence from Molecular Aggregates (South China University of Technology), Guangzhou 510640, China
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26
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Metin E, Arsu N, Catak S, Aviyente V. Photophysical, kinetic and thermodynamic study of one-component Type II thioxanthone acetic acid photoinitiators. Eur Polym J 2020. [DOI: 10.1016/j.eurpolymj.2020.109909] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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27
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Su L, Cao F, Cheng C, Tsuboi T, Zhu Y, Deng C, Zheng X, Wang D, Liu Z, Zhang Q. High Fluorescence Rate of Thermally Activated Delayed Fluorescence Emitters for Efficient and Stable Blue OLEDs. ACS APPLIED MATERIALS & INTERFACES 2020; 12:31706-31715. [PMID: 32567302 DOI: 10.1021/acsami.0c07840] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
A lack of an efficient and stable blue device is a critical factor restricting the development of organic light-emitting diode (OLED) technology that is currently expected to be overcome by employing thermally activated delayed fluorescence (TADF). Here, we investigate the TADF and electroluminescence (EL) performance of six carbazole/triphenyltriazine derivatives in different hosts. A good linearity between lg(LT50/kF2) and the EL emission wavelength is found, where LT50 is the half-life of the devices and kF is the fluorescence rate of the emitters, suggesting the dominance of the singlet exciton energy and lifetime in device stability. An indolylcarbazole/triphenyltriazine derivative (ICz-TRZ) with the capability to suppress solid-state solvation exhibits blue-shifted emission and an increased kF (1.5 × 108 s-1) in comparison to the control emitters in doped films. ICz-TRZ-based devices achieve a maximum external quantum efficiency (EQE) of 18% and an EQE of 5.5% at a very high luminance of 7 × 104 cd/m2. Ignoring the poor electrochemical stability of ICz-TRZ, the device offers an LT50 approaching 100 h under an initial luminance of 1000 cd/m2 and CIE coordinates of (0.14, 0.19). The findings in this work suggest that computer-aided design of high kF TADF emitters can be an approach to realize efficient and stable blue OLEDs.
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Affiliation(s)
- Liwu Su
- MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Fangyi Cao
- MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, Zhejiang 310027, China
- Yungu (Gu'an) Technology Co. Ltd., Langfang, Hebei 065500, China
| | - Cong Cheng
- MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Taiju Tsuboi
- MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Yunhui Zhu
- MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Chao Deng
- MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Xinyuan Zheng
- MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Dan Wang
- MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Zhang Liu
- MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Qisheng Zhang
- MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, Zhejiang 310027, China
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Lei Y, Dai W, Guan J, Guo S, Ren F, Zhou Y, Shi J, Tong B, Cai Z, Zheng J, Dong Y. Wide‐Range Color‐Tunable Organic Phosphorescence Materials for Printable and Writable Security Inks. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202003585] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- Yunxiang Lei
- Beijing Key Laboratory of Construction Tailorable Advanced Functional Materials and Green Applications School of Materials Science & Engineering Beijing Institute of Technology Beijing 100081 China
| | - Wenbo Dai
- Beijing Key Laboratory of Construction Tailorable Advanced Functional Materials and Green Applications School of Materials Science & Engineering Beijing Institute of Technology Beijing 100081 China
| | - Jianxin Guan
- Beijing National Laboratory for Molecular Sciences College of Chemistry and Molecular Engineering Peking University Beijing 100871 China
| | - Shuai Guo
- Beijing Key Laboratory of Construction Tailorable Advanced Functional Materials and Green Applications School of Materials Science & Engineering Beijing Institute of Technology Beijing 100081 China
| | - Fei Ren
- Beijing Key Laboratory of Construction Tailorable Advanced Functional Materials and Green Applications School of Materials Science & Engineering Beijing Institute of Technology Beijing 100081 China
| | - Yudai Zhou
- Beijing Key Laboratory of Construction Tailorable Advanced Functional Materials and Green Applications School of Materials Science & Engineering Beijing Institute of Technology Beijing 100081 China
| | - Jianbing Shi
- Beijing Key Laboratory of Construction Tailorable Advanced Functional Materials and Green Applications School of Materials Science & Engineering Beijing Institute of Technology Beijing 100081 China
| | - Bin Tong
- Beijing Key Laboratory of Construction Tailorable Advanced Functional Materials and Green Applications School of Materials Science & Engineering Beijing Institute of Technology Beijing 100081 China
| | - Zhengxu Cai
- Beijing Key Laboratory of Construction Tailorable Advanced Functional Materials and Green Applications School of Materials Science & Engineering Beijing Institute of Technology Beijing 100081 China
| | - Junrong Zheng
- Beijing National Laboratory for Molecular Sciences College of Chemistry and Molecular Engineering Peking University Beijing 100871 China
| | - Yuping Dong
- Beijing Key Laboratory of Construction Tailorable Advanced Functional Materials and Green Applications School of Materials Science & Engineering Beijing Institute of Technology Beijing 100081 China
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29
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Lei Y, Dai W, Guan J, Guo S, Ren F, Zhou Y, Shi J, Tong B, Cai Z, Zheng J, Dong Y. Wide-Range Color-Tunable Organic Phosphorescence Materials for Printable and Writable Security Inks. Angew Chem Int Ed Engl 2020; 59:16054-16060. [PMID: 32500576 DOI: 10.1002/anie.202003585] [Citation(s) in RCA: 176] [Impact Index Per Article: 44.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Indexed: 12/25/2022]
Abstract
Organic materials with long-lived, color-tunable phosphorescence are potentially useful for optical recording, anti-counterfeiting, and bioimaging. Herein, we develop a series of novel host-guest organic phosphors allowing dynamic color tuning from the cyan (502 nm) to orange red (608 nm). Guest materials are employed to tune the phosphorescent color, while the host materials interact with the guest to activate the phosphorescence emission. These organic phosphors have an ultra-long lifetime of 0.7 s and a maximum phosphorescence efficiency of 18.2 %. Although color-tunable inks have already been developed using visible dyes, solution-processed security inks that are temperature dependent and display time-resolved printed images are unprecedented. This strategy can provide a crucial step towards the next-generation of security technologies for information handling.
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Affiliation(s)
- Yunxiang Lei
- Beijing Key Laboratory of Construction Tailorable Advanced Functional Materials and Green Applications, School of Materials Science & Engineering, Beijing Institute of Technology, Beijing, 100081, China
| | - Wenbo Dai
- Beijing Key Laboratory of Construction Tailorable Advanced Functional Materials and Green Applications, School of Materials Science & Engineering, Beijing Institute of Technology, Beijing, 100081, China
| | - Jianxin Guan
- Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, China
| | - Shuai Guo
- Beijing Key Laboratory of Construction Tailorable Advanced Functional Materials and Green Applications, School of Materials Science & Engineering, Beijing Institute of Technology, Beijing, 100081, China
| | - Fei Ren
- Beijing Key Laboratory of Construction Tailorable Advanced Functional Materials and Green Applications, School of Materials Science & Engineering, Beijing Institute of Technology, Beijing, 100081, China
| | - Yudai Zhou
- Beijing Key Laboratory of Construction Tailorable Advanced Functional Materials and Green Applications, School of Materials Science & Engineering, Beijing Institute of Technology, Beijing, 100081, China
| | - Jianbing Shi
- Beijing Key Laboratory of Construction Tailorable Advanced Functional Materials and Green Applications, School of Materials Science & Engineering, Beijing Institute of Technology, Beijing, 100081, China
| | - Bin Tong
- Beijing Key Laboratory of Construction Tailorable Advanced Functional Materials and Green Applications, School of Materials Science & Engineering, Beijing Institute of Technology, Beijing, 100081, China
| | - Zhengxu Cai
- Beijing Key Laboratory of Construction Tailorable Advanced Functional Materials and Green Applications, School of Materials Science & Engineering, Beijing Institute of Technology, Beijing, 100081, China
| | - Junrong Zheng
- Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, China
| | - Yuping Dong
- Beijing Key Laboratory of Construction Tailorable Advanced Functional Materials and Green Applications, School of Materials Science & Engineering, Beijing Institute of Technology, Beijing, 100081, China
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30
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Cho E, Coropceanu V, Brédas JL. Electronic Structure of Multicomponent Organic Molecular Materials: Evaluation of Range-Separated Hybrid Functionals. J Chem Theory Comput 2020; 16:3712-3719. [DOI: 10.1021/acs.jctc.0c00138] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Eunkyung Cho
- Department of Chemistry and Biochemistry, The University of Arizona, Tucson, Arizona 85721-0088, United States
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, United States
| | - Veaceslav Coropceanu
- Department of Chemistry and Biochemistry, The University of Arizona, Tucson, Arizona 85721-0088, United States
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, United States
| | - Jean-Luc Brédas
- Department of Chemistry and Biochemistry, The University of Arizona, Tucson, Arizona 85721-0088, United States
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, United States
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31
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Begam K, Bhandari S, Maiti B, Dunietz BD. Screened Range-Separated Hybrid Functional with Polarizable Continuum Model Overcomes Challenges in Describing Triplet Excitations in the Condensed Phase Using TDDFT. J Chem Theory Comput 2020; 16:3287-3293. [DOI: 10.1021/acs.jctc.0c00086] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Affiliation(s)
- Khadiza Begam
- Department of Physics, Kent State University, Kent, Ohio 44242, United States
| | - Srijana Bhandari
- Department of Chemistry and Biochemistry, Kent State University, Kent, Ohio 44242, United States
| | - Buddhadev Maiti
- Department of Chemistry and Biochemistry, Kent State University, Kent, Ohio 44242, United States
| | - Barry D. Dunietz
- Department of Chemistry and Biochemistry, Kent State University, Kent, Ohio 44242, United States
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Feng S, Guo X, Zhang J. An effective strategy for simply varying relative position of two carbazole groups in the thermally activated delayed fluorescence emitters to achieve deep-blue emission. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2020; 226:117564. [PMID: 31614274 DOI: 10.1016/j.saa.2019.117564] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/23/2019] [Revised: 09/16/2019] [Accepted: 09/22/2019] [Indexed: 06/10/2023]
Abstract
The development of efficient deep-blue thermally activated delayed fluorescence (TADF) materials is especially important for organic light-emitting devices as displays and lighting sources. However, finding suitable deep-blue TADF emitters is still challenging. Based on an experimentally reported blue-light TADF emitter DCZ-TTR, two new molecules (DCZ1-TTR and DCZ2-TTR) have been designed to investigate the impact of the change of relative position in two carbazole groups on their TADF properties. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations coupled with the Marcus rate theory have been performed. It is found that the absorption and emission spectra simulated using the BMK functional can reproduce the available experimental data very well. The fluorescence emissions of DCZ1-TTR and DCZ2-TTR are predicted to show clear blue-shifting in cyclohexane with respect to their analogue DCZ-TTR. Especially, the emission wavelength of DCZ2-TTR is calculated to be 435nm, in the deep-blue light range. According to the Marcus rate theory, the rates of reverse intersystem crossing of DCZ1-TTR and DCZ2-TTR are estimated to be two orders of magnitude larger than that of DCZ-TTR, which is more favorable for the occurrence of delayed fluorescence. This strongly suggests that our newly designed two molecules DCZ1-TTR and DCZ2-TTR can be also expected to be potential blue-light or even deep-blue-light TADF emitters. This may be an effective strategy for realizing deep-blue emission by simply varying relative position of two carbazole groups in the TADF molecules. To our best knowledge, this is a novel finding, which may be useful in preparing highly efficient deep-blue TADF-OLED materials.
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Affiliation(s)
- Songyan Feng
- Institute of Upconversion Nanoscale Materials, Henan Provincial Engineering Research Center of Green Anticorrosion Technology for Magnesium Alloy, College of Chemistry and Chemical Engineering, Henan University, Kaifeng, 475004, PR China
| | - Xugeng Guo
- Institute of Upconversion Nanoscale Materials, Henan Provincial Engineering Research Center of Green Anticorrosion Technology for Magnesium Alloy, College of Chemistry and Chemical Engineering, Henan University, Kaifeng, 475004, PR China.
| | - Jinglai Zhang
- Institute of Upconversion Nanoscale Materials, Henan Provincial Engineering Research Center of Green Anticorrosion Technology for Magnesium Alloy, College of Chemistry and Chemical Engineering, Henan University, Kaifeng, 475004, PR China.
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33
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Zhang X, Shi Y, Cai L, Zhou Y, Wang CK, Lin L. Solvent effect on the photophysical properties of thermally activated delayed fluorescence molecules. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2020; 225:117473. [PMID: 31470345 DOI: 10.1016/j.saa.2019.117473] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2019] [Revised: 07/27/2019] [Accepted: 08/15/2019] [Indexed: 06/10/2023]
Abstract
As the third-generation organic electroluminescent materials, thermally activated delayed fluorescence (TADF) molecules have become the research focus recently. Significant solvent effect on TADF molecules were found experimentally, while theoretical investigations are quite limited. In this work, the solvent effect on photophysical properties of DCBPy and DTCBPy are investigated with first-principles calculations. The solvent polarity has slight influence on the molecular geometries and orbitals, while it can decrease the energy gap between the first singlet excited state (S1) and first triplet excited state (T1) significantly. Both the oscillator strength and the radiation rates of S1 increase with larger solvent polarity. The large energy gap between S1 and T1 induce negligible intersystem crossing (ISC) and reverse ISC rates between them, which also indicates higher triplet excited states are involved in the up-conversion process. Our results provide valuable information about solvent influence on the light-emitting properties of TADF molecules, which could help one better understand the light-emitting mechanism of them and favor the design of TADF molecules.
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Affiliation(s)
- Xiaotong Zhang
- Shandong Province Key Laboratory of Medical Physics and Image Processing Technology, School of Physics and Electronics, Shandong Normal University, 250014 Jinan, China
| | - Yurong Shi
- Shandong Province Key Laboratory of Medical Physics and Image Processing Technology, School of Physics and Electronics, Shandong Normal University, 250014 Jinan, China
| | - Lei Cai
- Shandong Province Key Laboratory of Medical Physics and Image Processing Technology, School of Physics and Electronics, Shandong Normal University, 250014 Jinan, China
| | - Yong Zhou
- Shandong Province Key Laboratory of Medical Physics and Image Processing Technology, School of Physics and Electronics, Shandong Normal University, 250014 Jinan, China
| | - Chuan-Kui Wang
- Shandong Province Key Laboratory of Medical Physics and Image Processing Technology, School of Physics and Electronics, Shandong Normal University, 250014 Jinan, China.
| | - Lili Lin
- Shandong Province Key Laboratory of Medical Physics and Image Processing Technology, School of Physics and Electronics, Shandong Normal University, 250014 Jinan, China.
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34
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Abroshan H, Cho E, Coropceanu V, Brédas J. Suppression of Concentration Quenching in Ortho‐Substituted Thermally Activated Delayed Fluorescence Emitters. ADVANCED THEORY AND SIMULATIONS 2019. [DOI: 10.1002/adts.201900185] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Affiliation(s)
- Hadi Abroshan
- School of Chemistry and Biochemistry Center for Organic Photonics and Electronics Georgia Institute of Technology Atlanta GA 30332‐0400 USA
| | - Eunkyung Cho
- School of Chemistry and Biochemistry Center for Organic Photonics and Electronics Georgia Institute of Technology Atlanta GA 30332‐0400 USA
| | - Veaceslav Coropceanu
- School of Chemistry and Biochemistry Center for Organic Photonics and Electronics Georgia Institute of Technology Atlanta GA 30332‐0400 USA
| | - Jean‐Luc Brédas
- School of Chemistry and Biochemistry Center for Organic Photonics and Electronics Georgia Institute of Technology Atlanta GA 30332‐0400 USA
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35
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de Silva P. Inverted Singlet-Triplet Gaps and Their Relevance to Thermally Activated Delayed Fluorescence. J Phys Chem Lett 2019; 10:5674-5679. [PMID: 31483656 DOI: 10.1021/acs.jpclett.9b02333] [Citation(s) in RCA: 81] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The basic design principle for emitters exhibiting thermally activated delayed fluorescence (TADF) is the minimization of the singlet-triplet gap. While typically this gap is positive, a possible inversion of states has been proposed as a pathway to improve the efficiency of organic light-emitting diodes. Despite the efforts to design such emitters, there are very few reports indicating that it is at all possible. We analyze the problem of the gap inversion from the perspective of the electronic structure theory. The key result is that inversion is possible but requires a substantial contribution of double excitations and that commonly used cheap electronic structure methods would fail to predict it.
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Affiliation(s)
- Piotr de Silva
- Department of Energy Conversion and Storage , Technical University of Denmark , Fysikvej 309 , 2800 Kongens Lyngby , Denmark
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36
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Guo H, Peng Q, Chen XK, Gu Q, Dong S, Evans EW, Gillett AJ, Ai X, Zhang M, Credgington D, Coropceanu V, Friend RH, Brédas JL, Li F. High stability and luminescence efficiency in donor-acceptor neutral radicals not following the Aufbau principle. NATURE MATERIALS 2019; 18:977-984. [PMID: 31332338 DOI: 10.1038/s41563-019-0433-1] [Citation(s) in RCA: 125] [Impact Index Per Article: 25.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2018] [Accepted: 06/13/2019] [Indexed: 06/10/2023]
Abstract
With their unusual electronic structures, organic radical molecules display luminescence properties potentially relevant to lighting applications; yet, their luminescence quantum yield and stability lag behind those of other organic emitters. Here, we designed donor-acceptor neutral radicals based on an electron-poor perchlorotriphenylmethyl or tris(2,4,6-trichlorophenyl)methyl radical moiety combined with different electron-rich groups. Experimental and quantum-chemical studies demonstrate that the molecules do not follow the Aufbau principle: the singly occupied molecular orbital is found to lie below the highest (doubly) occupied molecular orbital. These donor-acceptor radicals have a strong emission yield (up to 54%) and high photostability, with estimated half-lives reaching up to several months under pulsed ultraviolet laser irradiation. Organic light-emitting diodes based on such a radical emitter show deep-red/near-infrared emission with a maximal external quantum efficiency of 5.3%. Our results provide a simple molecular-design strategy for stable, highly luminescent radicals with non-Aufbau electronic structures.
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Affiliation(s)
- Haoqing Guo
- State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun, China
| | - Qiming Peng
- State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun, China
- Key Laboratory of Flexible Electronics (KLOFE) & Institute of Advanced Materials (IAM), Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing Tech University (NanjingTech), Nanjing, China
| | - Xian-Kai Chen
- School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, GA, USA
| | - Qinying Gu
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | - Shengzhi Dong
- State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun, China
| | - Emrys W Evans
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | | | - Xin Ai
- State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun, China
| | - Ming Zhang
- State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun, China
| | - Dan Credgington
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | - Veaceslav Coropceanu
- School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, GA, USA
| | | | - Jean-Luc Brédas
- School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, GA, USA.
| | - Feng Li
- State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun, China.
- Cavendish Laboratory, University of Cambridge, Cambridge, UK.
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37
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Ahn CH, Kim D. Role of the Geometry Restriction and Quasi‐Degeneracy of the Excited States in Thermally Activated Delayed Fluorescence: A Density Functional Theory Study of Carbzolyl‐Bispyridinylmethanone Derivatives. CHEMPHOTOCHEM 2019. [DOI: 10.1002/cptc.201900099] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Chang Hwan Ahn
- Department of ChemistryKyonggi University 154-42, Gwanggyosan-ro, Yeongtong-gu Suwon 16227 Korea
| | - Dongwook Kim
- Department of ChemistryKyonggi University 154-42, Gwanggyosan-ro, Yeongtong-gu Suwon 16227 Korea
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38
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Liu J, Zhou K, Wang D, Deng C, Duan K, Ai Q, Zhang Q. Pyrazine-Based Blue Thermally Activated Delayed Fluorescence Materials: Combine Small Singlet-Triplet Splitting With Large Fluorescence Rate. Front Chem 2019; 7:312. [PMID: 31165054 PMCID: PMC6536661 DOI: 10.3389/fchem.2019.00312] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2019] [Accepted: 04/18/2019] [Indexed: 01/21/2023] Open
Abstract
Metal-free thermally activated delayed fluorescence (TADF) emitters have emerged as promising candidate materials for highly efficient and low-cost organic light-emitting diodes (OLEDs). Here, a novel acceptor 2-cyanopyrazine is selected for the construction of blue TADF molecules via computer-assisted molecular design. Both theoretical prediction and experimental photophysical data indicate a small S1-T1 energy gap (ΔEST) and a relative large fluorescence rate (kF) in an o-phenylene-bridged 2-cyanopyrazine/3,6-di-tert-butylcarbazole compound (TCzPZCN). The kF value of 3.7 × 107 s−1 observed in a TCzPZCN doped film is among the highest in the TADF emitters with a ΔEST smaller than 0.1 eV. Blue TADF emission is observed in a TCzPZCN doped film with a short TADF lifetime of 1.9 μs. The OLEDs using TCzPZCN as emitter exhibit a maximum external quantum efficiency (EQE) of 7.6% with low-efficiency roll-off. A sky-blue device containing a derivative of TCzPZCN achieves an improved EQE maximum of 12.2% by suppressing the non-radiative decay at T1.
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Affiliation(s)
- Junyuan Liu
- MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, China
| | - Keren Zhou
- MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, China
| | - Dan Wang
- MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, China
| | - Chao Deng
- MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, China
| | - Ke Duan
- MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, China
| | - Qi Ai
- MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, China
| | - Qisheng Zhang
- MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, China
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39
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Yurash B, Nakanotani H, Olivier Y, Beljonne D, Adachi C, Nguyen TQ. Photoluminescence Quenching Probes Spin Conversion and Exciton Dynamics in Thermally Activated Delayed Fluorescence Materials. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2019; 31:e1804490. [PMID: 30957291 DOI: 10.1002/adma.201804490] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2018] [Revised: 09/05/2018] [Indexed: 06/09/2023]
Abstract
Fluorescent materials that efficiently convert triplet excitons into singlets through reverse intersystem crossing (RISC) rival the efficiencies of phosphorescent state-of-the-art organic light-emitting diodes. This upconversion process, a phenomenon known as thermally activated delayed fluorescence (TADF), is dictated by the rate of RISC, a material-dependent property that is challenging to determine experimentally. In this work, a new analytical model is developed which unambiguously determines the magnitude of RISC, as well as several other important photophysical parameters such as exciton diffusion coefficients and lengths, all from straightforward time-resolved photoluminescence measurements. From a detailed investigation of five TADF materials, important structure-property relationships are derived and a brominated derivative of 2,4,5,6-tetrakis(carbazol-9-yl)isophthalonitrile that has an exciton diffusion length of over 40 nm and whose excitons interconvert between the singlet and triplet states ≈36 times during one lifetime is identified.
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Affiliation(s)
- Brett Yurash
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA, 93106, USA
| | - Hajime Nakanotani
- Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, 744 Motooka, Nishi, Fukuoka, 819-0395, Japan
| | - Yoann Olivier
- Laboratory for Chemistry of Novel Materials, University of Mons, Place du Parc 20, B-7000, Mons, Belgium
| | - David Beljonne
- Laboratory for Chemistry of Novel Materials, University of Mons, Place du Parc 20, B-7000, Mons, Belgium
| | - Chihaya Adachi
- Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, 744 Motooka, Nishi, Fukuoka, 819-0395, Japan
| | - Thuc-Quyen Nguyen
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA, 93106, USA
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40
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Bella AP, Solomon RV, Vedha SA, Merlin JP. Enhanced luminescence efficiency of structurally tailored new coumarin-based heterocyclic organic materials: a DFT/TD-DFT study. Theor Chem Acc 2019. [DOI: 10.1007/s00214-019-2448-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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41
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Lv L, Yuan K, Zhu Y, Zuo G, Wang Y. Investigation of Conversion and Decay Processes in Thermally Activated Delayed Fluorescence Copper(I) Molecular Crystal: Theoretical Estimations from an ONIOM Approach Combined with the Tuned Range-Separated Density Functional Theory. J Phys Chem A 2019; 123:2080-2090. [DOI: 10.1021/acs.jpca.9b00321] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- Lingling Lv
- College of Chemical Engineering and Technology, Tianshui Normal University, Tianshui, Gansu 741001, China
- Supercomputing Center for Theoretical Chemistry, Tianshui Normal University, Tianshui, GanSu 741001, China
| | - Kun Yuan
- College of Chemical Engineering and Technology, Tianshui Normal University, Tianshui, Gansu 741001, China
- Supercomputing Center for Theoretical Chemistry, Tianshui Normal University, Tianshui, GanSu 741001, China
| | - Yuancheng Zhu
- College of Chemical Engineering and Technology, Tianshui Normal University, Tianshui, Gansu 741001, China
- Supercomputing Center for Theoretical Chemistry, Tianshui Normal University, Tianshui, GanSu 741001, China
| | - Guofang Zuo
- College of Chemical Engineering and Technology, Tianshui Normal University, Tianshui, Gansu 741001, China
| | - Yongcheng Wang
- College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, Gansu 730070, China
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Lin Z, Van Voorhis T. Triplet Tuning: A Novel Family of Non-Empirical Exchange–Correlation Functionals. J Chem Theory Comput 2019; 15:1226-1241. [DOI: 10.1021/acs.jctc.8b00853] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Affiliation(s)
- Zhou Lin
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Troy Van Voorhis
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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Olivier Y, Sancho-Garcia JC, Muccioli L, D'Avino G, Beljonne D. Computational Design of Thermally Activated Delayed Fluorescence Materials: The Challenges Ahead. J Phys Chem Lett 2018; 9:6149-6163. [PMID: 30265539 DOI: 10.1021/acs.jpclett.8b02327] [Citation(s) in RCA: 73] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Thermally activated delayed fluorescence (TADF) offers promise for all-organic light-emitting diodes with quantum efficiencies competing with those of transition-metal-based phosphorescent devices. While computational efforts have so far largely focused on gas-phase calculations of singlet and triplet excitation energies, the design of TADF materials requires multiple methodological developments targeting among others a quantitative description of electronic excitation energetics, fully accounting for environmental electrostatics and molecular conformational effects, the accurate assessment of the quantum mechanical interactions that trigger the elementary electronic processes involved in TADF, and a robust picture for the dynamics of these fundamental processes. In this Perspective, we describe some recent progress along those lines and highlight the main challenges ahead for modeling, which we hope will be useful to the whole TADF community.
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Affiliation(s)
- Y Olivier
- Laboratory for Chemistry of Novel Materials , University of Mons , Place du Parc 20 , B-7000 Mons , Belgium
| | - J-C Sancho-Garcia
- Departamento de Química Física , Universidad de Alicante , E-03080 Alicante , Spain
| | - L Muccioli
- Dipartimento di Chimica Industriale "Toso Montanari" , Università di Bologna , I-40136 Bologna , Italy
- Institut des Sciences Moléculaires, UMR 5255 , University of Bordeaux , F- 33405 Talence , France
| | - G D'Avino
- Institut Néel, CNRS and Grenoble Alpes University, F-38042 Grenoble , France
| | - D Beljonne
- Laboratory for Chemistry of Novel Materials , University of Mons , Place du Parc 20 , B-7000 Mons , Belgium
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Sontakke AD, Mouesca JM, Castaing V, Ferrier A, Salaün M, Gautier-Luneau I, Maurel V, Ibanez A, Viana B. Time-gated triplet-state optical spectroscopy to decipher organic luminophores embedded in rigid matrices. Phys Chem Chem Phys 2018; 20:23294-23300. [PMID: 30198536 DOI: 10.1039/c8cp03952f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Wet-chemically synthesized inorganic materials often exhibit luminescence behavior. We have recently shown that the amorphous yttrium-aluminium-borate (a-YAB) powders obtained by sol-gel and modified Pechini methods exhibit organic impurities, responsible for their intense visible photoluminescence and phosphorescence afterglow. However, the heterogeneity of impurity organic compounds and difficulties in their intact extraction from the solid inorganic host matrix limit the extraction-based chemical analysis for luminophore identification. Here, we propose a photo-physical route based on time-gated triplet-state optical spectroscopy (TGTSS) to construct the electronic structures of the trapped unknown luminophores, which successfully illustrates the luminescence properties of a-YAB powders in more detail and also provides important insights intrinsic to the nature of the luminophores. The experimental results accompanied with TD-DFT calculations of the theoretical electronic structures thus help us to propose the probable luminophore compounds trapped in rigid a-YAB matrices. We anticipate that the present approach will open new opportunities for analyzing similar complex luminescent materials, including carbon dots, graphene oxides, etc., which is vital for their improvement.
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Affiliation(s)
- Atul D Sontakke
- PSL Research University, Chimie ParisTech - CNRS, Institut de Recherche de Chimie Paris, 75005 Paris, France.
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Chen XK, Kim D, Brédas JL. Thermally Activated Delayed Fluorescence (TADF) Path toward Efficient Electroluminescence in Purely Organic Materials: Molecular Level Insight. Acc Chem Res 2018; 51:2215-2224. [PMID: 30141908 DOI: 10.1021/acs.accounts.8b00174] [Citation(s) in RCA: 215] [Impact Index Per Article: 35.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Since the seminal work of Tang and Vanslyke in 1987 on small-molecule emitters and that of Friend and co-workers in 1990 on conjugated-polymer emitters, organic light-emitting diodes (OLEDs) have attracted much attention from academia as well as industry, as the OLED market is estimated to reach the $30 billion mark by the end of 2018. In these first-generation organic emitters, on the basis of simple spin statistics, electrical excitation resulted in the formation of ∼25% singlet excitons and ∼75% triplet excitons. Radiative decay of the singlet excitons to the singlet ground state leads to a prompt fluorescence emission, while the triplet excitons only lead to weak phosphorescence due to the very small spin-orbit couplings present in purely organic molecules. The consequence is a ca. 75% energy loss, which triggered wide-ranging efforts to try and harvest as many of the triplet excitons as possible. In 1998, Thompson, Forrest, and their co-workers reported second-generation OLED emitters based on coordination complexes with heavy transition metals (e.g., iridium or platinum). Here, the triplet excitons stimulate efficient and fast phosphorescence due to the strong spin-orbit couplings enabled by the heavy-metal atoms. Internal quantum efficiencies (IQE) up to 100% have been reported, which means that for every electron injected into the device, a photon is emitted. While these second-generation emitters are those mainly exploited in current OLED applications, there is strong impetus from both cost and environmental standpoints to find new ways of exploiting purely organic emitters, which in addition can offer greater flexibility to fine-tune the electronic and optical properties by exploiting the synthetic organic chemistry toolbox. In 2012, Adachi and co-workers introduced a promising strategy, based on thermally activated delayed fluorescence (TADF), to harvest the triplet excitons in purely organic molecular materials. These materials now represent the third generation of OLED emitters. Impressive photophysical properties and device performances have been reported, with internal quantum efficiencies also reaching nearly 100%. Our objectives in this Account are threefold: (i) to lay out a comprehensive description, at the molecular level, of the fundamental photophysical processes behind TADF emitters; (ii) to discuss some of the challenges facing the design of TADF emitters, such as the need to balance the efficiency of thermal activation of triplet excitons into the singlet manifold with the efficiency of radiative transition to the ground state; and (iii) to highlight briefly some of the recent molecular-design strategies that pave the way to new classes of TADF materials.
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Affiliation(s)
- Xian-Kai Chen
- Center for Organic Photonics and Electronics and School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, United States
| | - Dongwook Kim
- Department of Chemistry, Kyonggi University, 154-42 Gwanggyosan-Ro, Yeongtong-Gu, Suwon 16227, Korea
| | - Jean-Luc Brédas
- Center for Organic Photonics and Electronics and School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, United States
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Zhou B, Hu Z, Jiang Y, Zhong C, Sun Z, Sun H. Theoretical exploitation of acceptors based on benzobis(thiadiazole) and derivatives for organic NIR-II fluorophores. Phys Chem Chem Phys 2018; 20:19759-19767. [PMID: 29998265 DOI: 10.1039/c8cp03135e] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Small-molecule dyes with fluorescence emission in the second near-infrared (NIR-II) region (1000-1700 nm) have attracted considerable attention in the biomedical and bioimaging fields due to their greater imaging depths, better spatial resolution, and higher signal-to-background ratios. However, currently reported organic NIR-II fluorophores are still limited and there is great demand to develop other novel NIR-II fluorophores besides benzobisthiadiazole (BBT)-based fluorophores. More importantly, there is a lack of an appropriate level of theory capable of providing both efficient and accurate predictions of the electronic structures of organic NIR-II fluorophores. In this work, successful application of time-dependent density functional theory (TDDFT) using optimally-tuned range-separated functionals for calculations of both absorption and fluorescence spectral properties has been demonstrated, compared with the available experimental data. A series of thiadiazole-based acceptors (A) and derivatives based on the D-A-D skeleton are designed coupled with the triphenylamine donor (D). The structure-property relationships for these fluorophores are thus revealed by analyzing their ground (S0) and excited (S1) state geometries, frontier molecular orbitals (HOMO and LUMO), HOMO-LUMO energy gaps, oscillator strengths, hole-electron distributions and fluorescence wavelengths. It is suggested that the existence of a hypervalent structure leading to a much lower LUMO level and accompanying significant hole-electron separation plays a key role in the red-shift of fluorescence emission in the NIR-II region. In addition, the substitution of BBT oligomers and analogues as acceptor cores is an efficient way to achieve both red-shifted fluorescence wavelengths and enhanced oscillator strengths. The present work provides a reliable and efficient theoretical tool for predicting the related electronic and spectral properties of organic fluorophores and future screening out of potential candidates for excellent NIR-II molecular fluorophores.
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Affiliation(s)
- Bin Zhou
- State Key Laboratory of Precision Spectroscopy, School of Physics and Materials Science, East China Normal University, Shanghai 200062, P. R. China.
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Minotto A, Murto P, Genene Z, Zampetti A, Carnicella G, Mammo W, Andersson MR, Wang E, Cacialli F. Efficient Near-Infrared Electroluminescence at 840 nm with "Metal-Free" Small-Molecule:Polymer Blends. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:e1706584. [PMID: 29987856 DOI: 10.1002/adma.201706584] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2017] [Revised: 03/24/2018] [Indexed: 06/08/2023]
Abstract
Due to the so-called energy-gap law and aggregation quenching, the efficiency of organic light-emitting diodes (OLEDs) emitting above 800 nm is significantly lower than that of visible ones. Successful exploitation of triplet emission in phosphorescent materials containing heavy metals has been reported, with OLEDs achieving remarkable external quantum efficiencies (EQEs) up to 3.8% (peak wavelength > 800 nm). For OLEDs incorporating fluorescent materials free from heavy or toxic metals, however, we are not aware of any report of EQEs over 1% (again for emission peaking at wavelengths > 800 nm), even for devices leveraging thermally activated delayed fluorescence (TADF). Here, the development of polymer light-emitting diodes (PLEDs) peaking at 840 nm and exhibiting unprecedented EQEs (in excess of 1.15%) and turn-on voltages as low as 1.7 V is reported. These incorporate a novel triazolobenzothiadiazole-based emitter and a novel indacenodithiophene-based transport polymer matrix, affording excellent spectral and transport properties. To the best of knowledge, such values are the best ever reported for electroluminescence at 840 nm with a purely organic and solution-processed active layer, not leveraging triplet-assisted emission.
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Affiliation(s)
- Alessandro Minotto
- Department Physics and Astronomy and London Centre for Nanotechnology, University College London, London, WC1H 0AH, UK
| | - Petri Murto
- Department of Chemistry and Chemical Engineering/Applied Chemistry, Chalmers University of Technology, Gothenburg, SE-412 96, Sweden
- Flinders Institute for NanoScale Science & Technology, Flinders University, Sturt Road, Bedford Park, Adelaide, SA, 5042, Australia
| | - Zewdneh Genene
- Department of Chemistry and Chemical Engineering/Applied Chemistry, Chalmers University of Technology, Gothenburg, SE-412 96, Sweden
- Department of Chemistry, Addis Ababa University, Addis Ababa, P.O. Box 33658, Ethiopia
| | - Andrea Zampetti
- Department Physics and Astronomy and London Centre for Nanotechnology, University College London, London, WC1H 0AH, UK
| | - Giuseppe Carnicella
- Department Physics and Astronomy and London Centre for Nanotechnology, University College London, London, WC1H 0AH, UK
| | - Wendimagegn Mammo
- Department of Chemistry, Addis Ababa University, Addis Ababa, P.O. Box 33658, Ethiopia
| | - Mats R Andersson
- Flinders Institute for NanoScale Science & Technology, Flinders University, Sturt Road, Bedford Park, Adelaide, SA, 5042, Australia
| | - Ergang Wang
- Department of Chemistry and Chemical Engineering/Applied Chemistry, Chalmers University of Technology, Gothenburg, SE-412 96, Sweden
| | - Franco Cacialli
- Department Physics and Astronomy and London Centre for Nanotechnology, University College London, London, WC1H 0AH, UK
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Mewes JM. Modeling TADF in organic emitters requires a careful consideration of the environment and going beyond the Franck-Condon approximation. Phys Chem Chem Phys 2018; 20:12454-12469. [PMID: 29700532 DOI: 10.1039/c8cp01792a] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The origin of the thermally-activated delayed fluorescence (TADF) of three organic emitters is investigated, focusing on the nature of the lowest excited states, their transition properties, as well as the role of the environment. For this purpose, the algebraic-diagrammatic construction for the polarization propagator at second order of perturbation theory [ADC(2)], time-dependent density-functional theory in the Tamm-Dancoff approximation (TDA) and unrestricted Kohn-Sham DFT in combination with the maximum-overlap method (ΔDFT) are employed. The influence of the dielectric environment is rigorously included using different variants of the polarizable continuum model. The calculations reveal the lowest excited singlet and triplet states of all studied emitters to be dominated by charge-transfer (CT) character already in the most apolar environment corresponding to cyclo-hexane. The dielectric stabilization entails a drastic reduction of the singlet-triplet gaps, increasing the calculated TADF rates by several orders of magnitude. Another ingredient for accurate TADF rates is hidden in the excited-state potential-energy surfaces along the donor-acceptor twisting angle. A presence of large, shallow plateaus in apolar environments causes the transition properties to be governed by thermal fluctuations rather than the minimum-energy geometries. This leads to a large increase of the oscillator strengths, as well as a breakdown of the Franck-Condon approximation. The last ingredient is a small but significant spin-orbit coupling (SOC) between the singlet and triplet CT states, which is traced back to a delocalization of the excitation hole or excited electron of the triplet CT state. Taking into account all of these effects, a reasonable agreement with experimental TADF and fluorescence lifetimes is obtained. For this, it proves to be sufficient to consider only the lowest lying singlet and triplet excited states.
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Affiliation(s)
- Jan-Michael Mewes
- Jan-Michael Mewes, Centre For Theoretical Chemistry and Physics, New-Zealand Institute for Advanced Study, Massey University (Albany), Private Bag 102-904, North Shore Mail Centre, 0632 Auckland, New Zealand.
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Wang C, Yuan Y. The influence of aggregation on the third-order nonlinear optical property of π-conjugated chromophores: the case of cyanine dyes. Phys Chem Chem Phys 2018; 20:16777-16785. [DOI: 10.1039/c8cp00770e] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The typical J cyanine aggregate is experimentally and theoretically found to have potential applications involving two photon absorption.
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Affiliation(s)
- Chao Wang
- MOE Key Laboratory of Macromolecular Synthesis and Functionalization
- Department of Polymer Science and Engineering
- Zhejiang University
- Hangzhou 310027
- China
| | - Yizhong Yuan
- Key Laboratory for Ultrafine Materials of Ministry of Education and Shanghai Key Laboratory of Advanced Polymeric Materials
- School of Materials Science and Engineering
- Department of Material Science and Engineering
- East China University of Science and Technology
- Shanghai
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