Oliveira Leonardo M F, Valverde Danillo, Costa Gustavo J, Borin Antonio Carlos
Department of Fundamental Chemistry, Institute of Chemistry, University of São Paulo, São Paulo, Brazil.
Unité de Chimie Physique Théorique et Structurale, Namur Institute of Structured Matter, Université de Namur, Namur, Belgium.
Photochem Photobiol. 2024 Mar-Apr;100(2):323-338. doi: 10.1111/php.13833. Epub 2023 Jul 4.
9H- and 7H-2,6-Diaminopurine (26DAP) photoinduced events in vacuum were studied at the MS-CASPT2/cc-pVDZ level of theory. The S (ππ* L ) state is initially populated evolving barrierless towards its minimum energy structure, from where two photochemical events can take place in both tautomers. The first is the return of the electronic population to the ground state via the C6 conical intersection (CI-C6). The second involves an internal conversion to the ground through the C2 conical intersection (CI-C2). According to our geodesic interpolated paths connecting the critical structures, the second route is less favorable in both tautomers, due to the presence of high energy barriers. Our calculations suggest a competition between fluorescence and ultrafast relaxation to the electronic ground state via internal conversion process. Based on our calculated potential energy surfaces and experimental excited state lifetimes from the literature, we can infer that the 7H- must have a greater fluorescence yield than the 9H-tautomer. We also explored the triplet state population mechanisms on the 7H-26DAP to understand their long-lived components observed experimentally.
在MS-CASPT2/cc-pVDZ理论水平下研究了9H-和7H-2,6-二氨基嘌呤（26DAP）在真空中的光诱导事件。S （ππ* L ）态最初被填充，朝着其最低能量结构无势垒地演化，在两种互变异构体中都可以从该结构发生两个光化学事件。第一个是电子布居通过C6锥形交叉点（CI-C6）回到基态。第二个涉及通过C2锥形交叉点（CI-C2）内转换到基态。根据我们连接关键结构的测地线插值路径，由于存在高能势垒，第二条路径在两种互变异构体中都不太有利。我们的计算表明荧光与通过内转换过程超快弛豫到电子基态之间存在竞争。基于我们计算的势能面和文献中的实验激发态寿命，我们可以推断7H-的荧光产率必定比9H-互变异构体更高。我们还探索了7H-26DAP上的三重态布居机制，以了解实验中观察到的它们的长寿命成分。
