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Influence of electron donating ability on reverse intersystem crossing rate for one kind of thermally activated delayed fluorescence molecules
Lili Lin
Author NameAffiliationE-mail
Lili Lin School of Physics and Electronic,Shandong Normal University,250014 Jinan,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-XTN 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-orbital coupling coefficients (Hso), one finds that the larger value of (Hso/?ES1-T1)2 is, the faster of RISC is. The results show that all investigated molecules are promising candidates as TADF molecules. Overall, a wise molecular design strategy is proposed that enlarging the delocalization of frontier molecular orbitals with well separated HOMO and LUMO can achieve a small ?ES1-T1 for TADF molecules.
Key words:  Thermally activated delayed fluorescence, donating ability, reverse intersystem crossing, spin-orbital coupling
FundProject:
Influence of electron donating ability on reverse intersystem crossing rate for one kind of thermally activated delayed fluorescence molecules
蔺丽丽
摘要:
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-XTN 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-orbital coupling coefficients (Hso), one finds that the larger value of (Hso/?ES1-T1)2 is, the faster of RISC is. The results show that all investigated molecules are promising candidates as TADF molecules. Overall, a wise molecular design strategy is proposed that enlarging the delocalization of frontier molecular orbitals with well separated HOMO and LUMO can achieve a small ?ES1-T1 for TADF molecules.
关键词:  Thermally activated delayed fluorescence, donating ability, reverse intersystem crossing, spin-orbital coupling
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