Radiationless deactivation channels of 2-thiocytosine in aqueous environment are revisited by means of quantum-chemical simulations of excited-state absorption spectra, and investigations of potential energy surfaces of the chromophore clustered with two water molecules using the algebraic diagrammatic construction method to the second-order (ADC(2)), and multireference configuration interaction with single and double excitations (MR-CISD) methods. We argue that interactions of explicit water molecules with thiocarbonyl group might enable water-chromophore electron transfer (WCET) which leads to formation of intersystem crossing that was not considered previously. This is the first example of a WCET process occurring in the triplet manifold of electronic states. This phenomenon might explain nonradiative decay of the triplet state population observed in thiopyrimidines in the absence of molecular oxygen. According to our calculations this WCET process might also entail a subsequent, virtually barrierless, electron-driven proton transfer (EDPT) resulting in the formation of hydroxyl radical which could further participate in photohydration or deamination reactions.

通过激发态吸收光谱的量子化学模拟，重新研究了2-硫代胞嘧啶在水环境中的无辐射失活通道，并使用代数图解法对第二个水分子簇生的生色团的势能面进行了研究。顺序（ADC（2）），以及具有单激励和双激励（MR-CISD）方法的多引用配置交互。我们认为显性水分子与硫羰基的相互作用可能使水-发色团电子转移（WCET）成为可能，这导致了以前未曾考虑过的系统间交叉的形成。这是在电子状态的三重态流形中发生WCET过程的第一个示例。这种现象可能解释了在没有分子氧的情况下在硫代嘧啶中观察到的三重态种群的非辐射衰变。根据我们的计算，这种WCET过程可能还需要随后进行的，几乎无障碍的电子驱动质子转移（EDPT），导致形成羟基自由基，该羟基自由基可能进一步参与光合或脱氨反应。