To identify the mechanisms for and to estimate the photochemical reaction efficiency of molecules in solid-state host materials is difficult. The objective of the present research was to measure the photogeneration efficiency of the methylviologen cation radical (MV+•) hosted in a semi-transparent hybrid film composed of MV2+ and saponite, a 2:1 clay mineral. MV+• is the one-electron reduced species of MV2+. MV+• was generated by UV irradiation of these films. The fluorescence intensity of MV2+ and the photogeneration efficiency of MV+• depended on the loading level of MV2+. When the loading level of MV2+ was high (75% of the cation exchange capacity (abbreviated as % CEC) of saponite), its fluorescence was reduced considerably because of the self-fluorescence quenching reaction, and the photogeneration efficiency of MV+• was relatively high (quantum yield φ = 3.5×10–2) compared to that of films with low adsorption density (10% CEC, φ = 1.1×10–2). Furthermore, when the loading level of MV2+ was very low (0.13% CEC), a self-fluorescence quenching reaction was not observed and MV+• was not generated. From these observations, one of the principal mechanisms of the self-quenching reaction and MV+• formation in saponite is the electron transfer reaction between excited MV2+ and adjacent MV2+ molecules in the ground state.

中文翻译：

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皂石粘土中甲基紫精的光还原：甲基紫精吸附密度对反应效率的影响

确定固态主体材料中分子的光化学反应效率的机制和估计是困难的。本研究的目的是测量甲基紫精阳离子自由基 (MV+•) 的光生效率，该自由基存在于由 MV2+ 和皂石（一种 2:1 粘土矿物）组成的半透明混合膜中。MV+• 是 MV2+ 的单电子还原物质。MV+• 是由这些薄膜的紫外线照射产生的。MV2+的荧光强度和MV+•的光生效率取决于MV2+的加载水平。当 MV2+ 的负载水平较高时（皂石阳离子交换容量的 75%（缩写为 %CEC）），由于自发荧光猝灭反应，其荧光显着降低，与低吸附密度（10% CEC，φ = 1.1×10-2）薄膜相比，MV+• 的光生效率相对较高（量子产率φ = 3.5×10-2）。此外，当 MV2+ 的负载水平非常低（0.13% CEC）时，没有观察到自荧光淬灭反应，也没有产生 MV+•。根据这些观察，皂石中自淬灭反应和 MV+• 形成的主要机制之一是激发态的 MV2+ 与相邻的基态 MV2+ 分子之间的电子转移反应。