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Influence of Electron Donating Ability on Reverse Intersystem Crossing Rate for One Kind of Thermally Activated Delayed Fluorescence Molecules
Ming-lang Wang,Jian-zhong Fan,Li-li Lin*
Author NameAffiliationE-mail
Ming-lang Wang Shandong Province Key Laboratory of Medical Physics and Image Processing Technology, School of Physics and Electronics, Shandong Normal University, Jinan 250014, China;Department of Electronics, Peking University, Beijing 100871, China  
Jian-zhong Fan Shandong Province Key Laboratory of Medical Physics and Image Processing Technology, School of Physics and Electronics, Shandong Normal University, Jinan 250014, China  
Li-li Lin* Shandong Province Key Laboratory of Medical Physics and Image Processing Technology, School of Physics and Electronics, Shandong Normal University, Jinan 250014, China linll@sdnu.edu.cn 
Abstract:
First-principles calculations are applied for investigating influence of electron donating ability of donor groups in eight thermally activated delayed fluorescence (TADF) molecules on their geometrical structures and transition properties as well as reverse intersystem crossing (RISC) processes. Results show that the diphenylamine substitution in the donor part can slightly change the bond angle but decrease bond length between donor and acceptor unit except for the lowest triplet state (T1) of carbazole-xanthone molecule. As the electron donating ability of donor groups is increased, the overlap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) is decreased. As the diphenylamine groups are added in donor part, the delocalization of HOMO is enlarged, which brings a decreased energy gap (△ES1-T1) between the lowest singlet excited state (S1) and T1 state. Furthermore, with the calculated spin-orbit coupling coefficient (Hso), one finds that the larger value of (<S1|Ĥso|T1>2)/(△ES1-T12) is, the faster the RISC is. The results show that all investigated molecules are promising candidates as TADF molecules. Overall, a wise molecular design strategy for TADF molecules, in which a small △ES1-T1 can be achieved by enlarging the delocalization of frontier molecular orbitals with large separation between HOMO and LUMO, is proposed.
Key words:  Thermally activated delayed fluorescence  Donating ability  Reverse intersystem crossing  Spin-orbit coupling
FundProject:This work was supported by the National Natural Science Foundation of China (No.11374195 and No.21403133), the Taishan Scholar Project of Shandong Province, the Promotive Research Fund for Excellent Young and Middle-aged Scientists of Shandong Province (No.BS2014CL001), and the General Financial Grant from the China Postdoctoral Science Foundation (No.2014M560571).
供电子能力对一类热活化延迟荧光分子反系间窜越速率的影响
王明朗,范建忠,蔺丽丽*
摘要:
本文基于第一性原理,研究了八个热活化延迟荧光分子的性质,揭示了基团供电子能力对分子几何构型、跃迁属性以及反系间窜越过程的影响.研究结果表明,对于咔唑和氧杂蒽酮组成的一类分子的最低三重激发态(T1)而言,供体基团的二苯胺取代,几乎不会改变供体和受体之间的夹角,但却可以减小供体和受体间的键长.基团供电子能力越强,最高占据分子轨道(HOMO)和最低未占据分子轨道(LUMO)间的轨道重叠度越小,最低单重激发态S1和T1之间的能差(△ES1-T1)越小.此外,供体基团上增加二苯胺能够增加HOMO的离域性,而且能够进一步地减小△ES1-T1.通过计算S1和T1之间的旋轨耦合系数(Hso),发现(<S1so|T1>2)/(△ES1-T12)数值越大,反系间窜越速率越大.计算表明八个分子都可能是高效的热活化延迟荧光分子.本文提出了一条高效热活化延迟荧光分子的设计策略,即分离HOMO和LUMO的分布和增加HOMO的离域性能够有效地减小S1-T1能差.
关键词:  热活化延迟荧光  供电子能力  反系间窜越  旋轨耦合
DOI:10.1063/1674-0068/31/cjcp1710191
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