Zhou Qiaohui, Zhou Miaomiao, Wei Yaxiong, Zhou Xiaoguo, Liu Shilin, Zhang Song, Zhang Bing
Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui 230026, China.
State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China.
Phys Chem Chem Phys. 2017 Jan 4;19(2):1516-1525. doi: 10.1039/c6cp06897a.
Solvent effects play a very important role in photochemical reactions and energy transfer processes in solution; however, these effects are rarely mentioned in the triplet-triplet annihilation (TTA) upconversion fluorescence experiments. In a typical TTA upconversion system of a photosensitizer of diiodo-Bodipy (I2-Bodipy) and a triplet acceptor of perylene, five common inert solvents, hexane, heptane, toluene, 1,4-dioxane, and dimethyl sulfoxide (DMSO), were used to investigate the solvent effects on the overall quantum yield of upconversion fluorescence. Femtosecond and nanosecond time-resolved transient difference absorption spectra were obtained to study the efficiencies of intersystem crossing (ISC) and triplet-triplet energy transfer (TTET). From the obtained upconversion fluorescence emission spectra, the overall TTA upconversion fluorescence quantum yield was derived. Among the five solvents, the upconversion quantum yield in dioxane is the highest at 19.16%, more than twice that that in toluene (8.75%). For the solvents hexane, heptane, toluene, and dioxane, the yields generally follow the sequences of polarity and viscosity. However, a very low upconversion quantum yield (1.51%) was observed in DMSO although the TTET process and fluorescence quantum yield of perylene in DMSO were almost as efficient as in dioxane. Based on density functional theory calculations, a reasonable explanation for these solvent effects was proposed.
溶剂效应在溶液中的光化学反应和能量转移过程中起着非常重要的作用；然而，在三重态-三重态湮灭（TTA）上转换荧光实验中，这些效应很少被提及。在二碘代-Bodipy（I2-Bodipy）光敏剂和苝三重态受体的典型TTA上转换体系中，使用了五种常见的惰性溶剂，己烷、庚烷、甲苯、1,4-二氧六环和二甲基亚砜（DMSO），来研究溶剂对上转换荧光总量子产率的影响。获得了飞秒和纳秒时间分辨瞬态差分吸收光谱，以研究系间窜越（ISC）和三重态-三重态能量转移（TTET）的效率。从获得的上转换荧光发射光谱中，推导出了总的TTA上转换荧光量子产率。在这五种溶剂中，二氧六环中的上转换量子产率最高，为19.16%，是甲苯中（8.75%）的两倍多。对于己烷、庚烷、甲苯和二氧六环这些溶剂，产率通常遵循极性和粘度的顺序。然而，在DMSO中观察到非常低的上转换量子产率（1.51%），尽管苝在DMSO中的TTET过程和荧光量子产率几乎与在二氧六环中一样高效。基于密度泛函理论计算，对这些溶剂效应提出了合理的解释。
