1、研究论文 Article *E-mail:;Tel.:18584332041.Received November 24,2022;published January 10,2023.Supporting information for this article is available free of charge via the Internet at http:/sioc-.Project supported by the National Natural Science Foundation of China for the General Program(No.21873036).国家
2、自然科学基金面上项目(No.21873036)资助.124 http:/sioc- 2023 Shanghai Institute of Organic Chemistry,Chinese Academy of Sciences Acta Chim.Sinica 2023,81,124130 化 学 学 报 化 学 学 报 ACTA CHIMICA SINICA 多共振热激活延迟荧光过程的理论研究 张少秦a 李美清b 周中军*,a 曲泽星*,a (a吉林大学化学学院 理论化学研究所 长春 130023)(b吉林省计算中心 长春 130012)摘要摘要 本工作借助第一性原理和动力学演化,系统地研
3、究了四个叔丁基-咔唑及吩噻嗪取代的硼-氮化合物(BCz-BN、2PTZ-BN、Cz-PTZ-BN 和 2Cz-PTZ-BN)的多共振热激活延迟荧光的高效发光机制.结果表明上述分子 T1与 T2间的内转换速率远大于其它辐射与非辐射速率,同时 T2到 S1的反向系间窜越速率也高于 T1到 S1的反向系间窜越速率,因此其多共振热激活延迟荧光过程应遵循 T1T2S1S0的路径.进一步动力学演化表明,T1与 T2之间的内转换主要发生在演化初期,随着时间的推移,能量逐渐由 T2向 S1转移,并最终在 S1完成荧光发射.上述研究揭示了多共振延迟荧光的微观本质,为未来设计及合成新的多共振热激活延迟荧光分子提供
4、了理论依据.关键词关键词 光致发光;多共振热激活延迟荧光;密度泛函理论;激发态;旋轨耦合;反向系间窜越 Theoretical Study on the Multiple Resonance Thermally Activated Delayed Theoretical Study on the Multiple Resonance Thermally Activated Delayed Fluorescence Process Fluorescence Process Zhang,Shaoqina Li,Meiqingb Zhou,Zhongjun*,a Qu,Zexing*,a (a In
5、stitute of Theoretical Chemistry,College of Chemistry,Jilin University,Changchun 130023,China)(b The Computing Center of Jilin Province,Changchun 130012,China)Abstract In recent years,the multiple resonance thermally activated delayed fluorescence(MR-TADF)has become a hot topic due to the high fluor
6、escence quantum yield and small Stokes shift.In traditional TADF molecules,the lowest triplet excited state(T1)can convert into the lowest singlet excited state(S1)through the reverse intersystem crossing(RISC),and then return to the ground state(S0)by the radiative fluorescence emission.However,rec
7、ent studies found that in MR-TADF molecules,the higher triplet excited state(T2)might play an important role.Thus,the detailed mechanism for the lumines-cence in MR-TADF molecules,especially for the effect of higher triplet excited state,has still been an indefinite problem.In this work,the luminesc
8、ence mechanism of four newly reported MR-TADF molecules(BCz-BN,2PTZ-BN,CZ-PTZ-BN and 2Cz-PTZ-BN)which are substituted by tert-butyl-carbazole and phenothiazine groups has been systematically investigated by the first-principle calculation and kinetic time evolution.The results showed that the phenot
9、hiazine group can significantly increase the spin-orbit coupling(SOC)and increase the fluorescence quantum yield.More importantly,by computing the rate constants for the TADF process,we found that the internal conversion(IC)rate between two triplet excited states(T1 and T2)is much faster than the ra
10、diative and non-radiative rates,and meanwhile the rate of the reverse intersystem crossing of T2S1 is also faster than the one of T1S1.Therefore,the TADF process of the above molecules should follow the T1T2S1S0 process.The above findings were also confirmed by the further kinetic time evolution.In
11、the early stage,the system was mainly dominated by the internal conversion between T1 and T2.With the time evolution,the energy gradually transferred from T2 to S1,and finally emitted fluorescence on S1.However,if T2 is not involved in the time evolution,the TADF process will be significantly slowed
12、 down,which could further confirm the importance of T2 in the TADF process.This work reveals the nature of the TADF process which could be of great importance for designing and synthesizing new TADF molecules.Keywords photoluminescence;multiple resonance thermally activated delayed fluorescence;dens
13、ity functional theory;excited state;spin-orbit coupling;reverse intersystem crossing 1 引言 热激活延迟荧光(Thermally Activated Delayed Flu-orescence,TADF)材料由于其内量子效率理论上可以达到 100%1,在有机发光二极管(OLED)领域有着广泛的应用前景,近年来备受青睐2.通常,热激活延迟荧光过程是处于最低三重激发态(T1)的激子在热辅助条件下通过反向系间窜越(RISC)到达最低单重激发态(S1),而后再从S1以辐射荧光的形式回到基态S0,即T1S1S0过程3.
14、因此,人们在设计热激活延迟荧光材料时,通常会考虑减小 S1和 T1之间的能隙 E(S1-T1)并增大 S1和DOI:10.6023/A22110472 化化 学学 学学 报报 研究论文 Acta Chim.Sinica 2023,81,124130 2023 Shanghai Institute of Organic Chemistry,Chinese Academy of Sciences http:/sioc- 125 T1之间旋轨耦合(SOC).传统的TADF材料是基于给-受体框架通过在分子内构建电荷转移(CT)态减小 E(S1-T1)来实现延迟荧光4.但由于电荷转移态的引入,传统的热激
15、活延迟荧光分子的半峰宽一般较大5.2016 年,Hatakeyama 等6报道了一类新型的热激活延迟荧光分子(DABNAs).该类分子通过在共轭体系中掺杂硼-氮原子,不仅可以实现较小的 E(S1-T1),而且还可以通过 硼-氮的多共振效应减小S0与S1两个电子态之间的构型差异,从而抑制分子骨架的伸缩振动,具有较小的半峰宽,因此这类 TADF 分子也被称为“多共振热激活延迟荧光”分子7.目前,该策略已经成为广大科研工作者设计高效热激活延迟荧光分子的主流思想8.多共振热激活延迟荧光的高效发光机制近年来受到了化学家们的广泛关注.目前,人们普遍认为多共振热激活延迟荧光分子与传统的 TADF 分子类似,
16、都遵循T1S1S0过程9.然而 Northey 等10通过对 5,9-二苯 基-5,9-二氮杂-13b-硼萘(DABNA-1)的热激活延迟荧光过程研究发现,更高能量的T2很可能对其TADF过程具有重要影响.近期,人们又合成了一系列新的多共振热激活延迟荧光分子,并且通过进一步理论计算发现 T2与S1的旋轨耦合常数(HSOC)更大,这也表明T2很可能参与多共振热激活延迟荧光过程11.最近,Shizu等12通过进一步的理论研究明确了T2参与了DABNA-1分子的热激活延迟荧光过程,他们认为 DABNA-1 分子在热辅助条件下生成的 T1,不直接通过系间窜越到达 S1,而是先经内转换到达T2,再由T2经过系间窜越到达S1,而后再以辐射形式到达 S0,即 T1T2S1S0过程.因此,对于多共振热激活延迟荧光的高效发光本质的认知,特别是 T2对于其发光过程的影响目前仍是一个争议性问题.本工作我们将以最新实验报道的叔丁基-咔唑(t-Cz)及吩噻嗪(PTZ)取代的四个硼-氮化合物(BCz-BN、2PTZ-BN、Cz-PTZ-BN 和 2Cz-PTZ-BN)13为例,通过第一性原理计算和动力学含时演化