STUDIES ON SELF-REPAIRING PHOTOINDUCED ELECTRON TRANSFER PROCESS FROM THIOKETONES

在甲基紫酮作用下，稳态光照射硫酮（吡啶硫酮等）通过自修复光诱导电子转移过程持续产生自由基阳离子。由于这种新型的光致电子转移过程不需要牺牲试剂，因此可以用于光能转换系统。在本项目中，我们通过稳态和激光闪光光解方法研究了新型光诱导电子转移过程的机理和优化。当前循环的第一步是电子从三重态激发的吡啶硫酮转移到电子受体，如甲基紫素。吡啶乙硫酮自由基阳离子的去质子化和二聚化产生二硫化物，由于吸热的反向电子转移过程，二硫化物对甲基紫离子自由基阳离子反应较弱。因此，生成的甲基紫素自由基阳离子在几百秒内缓慢衰变。产物分析和反应体系在不同pH条件下的动力学分析支持了所提出的反应机理。这种自修复的光诱导电子转移过程也可应用于光催化h原子构筑体系。4-吡啶硫酮和甲基紫素在醇存在下的稳态光解反应生成紫素自由基阳离子。紫丁香碱的自由基阳离子即使在黑暗中也没有完全衰变，表明醇被初始吡啶硫酮生成的硫基去质子化。这一发现表明醇的催化脱氢是通过自修复的光诱导电子转移过程进行的。

Steady-state light irradiation to thioketones (pyridinethiones etc.) in the presence of methylviologen dication generates radical cation persistently by self-repairing photoinduced electron transfer process. This novel photoinduced electron transfer process will be useful for light energy conversion systems, since the reaction system does not use sacrificial reagent. In the present project, we investigated the mechanism and optimization of the novel photoinduced electron transfer process by means of steady-state and laser-flash photolysis methods. The initial step of the present cycle is electron transfer from the triplet excited pyridinethiones to electron acceptors such as methylviologen. Deprotonation and dimerization of the radical cation of pyridinethiones generate disulfide which is less reactive to methylviologen radical cation due to the endothermic back electron transfer process. Thus, generated methylviologen radical cation decayed slowly over several hundred seconds. The proposed reaction mechanisms are supported by the products analysis and kinetic analysis of the reaction systems under the various pH conditions. The self-repairing photoinduced electron transfer process can be also applied to photocatalytic H-atom abstruction system. Steady-state photolysis of 4-pyridinethione and methylviologen in the presence of alcohol generated viologen radical cation. The radical cation of viologen did not decay completely even in the dark, indicating deprotonation of alcohol by the thio radical which was generated from initial pyridinethione. This finding indicates catalytic dehydrogenation of alcohol by the self-repairing photoinduced electron transfer process.