Instituto de Química, Universidade de São Paulo, Brazil.
J Phys Chem B. 2012 Dec 6;116(48):14000-7. doi: 10.1021/jp3091599. Epub 2012 Nov 19.
The photophysics of 8-azaadenine (8-AA) has been studied with the CASPT2//CASSCF protocol and ANO-L double-ζ basis sets. Stationary equilibrium structures, surface crossings, minimum energy paths, and linear interpolations have been used to study possible mechanisms to populate the lowest triplet state, T(1)(3)(ππ*), capable of sensitizing molecular oxygen. Our results show that two main mechanisms can occur after photoexcitation to the S(2)(1)(ππ*) state. The first one is through the S(2)/S(1) conical intersection (((1)ππ*/(1)nπ*)(CI)), leading to the S(1) ((1)nπ*) state minimum, (S(1) ((1)nπ*))(min), where a singlet-triplet crossing, ((1)nπ*/(3)ππ*)(STC), is accessible. The second one starts with the ((1)ππ*/(3)nπ*)(STC) at the (S(2)((1)ππ*))(min), from which the system can evolve to the (T(2) ((3)nπ*))(min), with subsequent population of the T(1) excited electronic state, due to the ((3)nπ*/(3)ππ*)(CI) conical intersection.
采用 CASPT2//CASSCF 协议和ANO-L 双 ζ 基组研究了 8-氮杂腺嘌呤（8-AA）的光物理性质。采用静止平衡结构、表面交叉、最低能量路径和线性插值方法，研究了可能的机制，以填充最低三重态 T(1)(3)(ππ*)，该态能够敏化分子氧。我们的结果表明，在光激发到 S(2)(1)(ππ*)态后，可能会发生两种主要机制。第一种机制是通过 S(2)/S(1) 锥形交叉 (((1)ππ*/(1)nπ*)(CI)) 发生，导致到达 S(1) ((1)nπ*) 态的最低能，即 (S(1) ((1)nπ*))(min)，其中可发生单重态-三重态交叉 ((1)nπ*/(3)ππ*)(STC)。第二种机制起始于 (S(2)((1)ππ*))(min) 处的 ((1)ππ*/(3)nπ*)(STC)，体系可由此演化到 (T(2) ((3)nπ*))(min)，随后由于 ((3)nπ*/(3)ππ*)(CI) 锥形交叉，T(1) 激发电子态被填充。
