Fatima Anam, Chakraborty Pratip, Xu Xinyue, Jones Garth A, Chambrier Isabelle, Logan Giorgia, Cammidge Andrew N, Smith Trevor, Hall Christopher R, Meech Stephen R
School of Chemistry, University of East Anglia, Norwich, Norfolk, England.
Department of Chemistry, University of Melbourne, Melbourne, Victoria, Australia.
Angew Chem Int Ed Engl. 2025 Sep 8;64(37):e202506137. doi: 10.1002/anie.202506137. Epub 2025 Jul 31.
Development of new and improved photoswitches for molecular photonics and photo-pharmaceutics is an increasingly important research objective. Recently a promising family of photoswitches based on the rhodanine motif was described. Here, the photophysics of a typical example are investigated by ultrafast UV and IR spectroscopy and quantum chemical calculations. Remarkably, the photophysics are very different to and more complex than those of closely related monomethine photoswitches, which relax by ultrafast internal conversion to the electronic ground state. In the rhodanine photoswitch, the allowed Franck-Condon excited state also relaxes on a sub-picosecond timescale, but the ground state is repopulated only after several hundred picoseconds. Instead, the Franck-Condon state relaxes through (at least) two intermediate states. These states are characterized by transient spectroscopy, and the reaction pathway is modeled by quantum chemical calculations. Comparison of calculated and measured IR data suggests that a triplet mediated isomerization pathway is responsible for the slow excited state dynamics. The triplet state is rapidly populated via coupling of a nearly degenerate nπ* state populated by ultrafast internal conversion from the bright ππ* state. This unexpected isomerization pathway has important implications for the synthesis, analysis, and application of rhodanine photoswitches.
开发用于分子光子学和光药理学的新型且改进的光开关是一个日益重要的研究目标。最近描述了一类基于若丹宁基序的有前景的光开关。在此，通过超快紫外和红外光谱以及量子化学计算研究了一个典型例子的光物理性质。值得注意的是，其光物理性质与密切相关的单甲川光开关的光物理性质非常不同且更为复杂，单甲川光开关通过超快内转换弛豫到电子基态。在若丹宁光开关中，允许的弗兰克 - 康登激发态也在亚皮秒时间尺度上弛豫，但基态仅在几百皮秒后重新填充。相反，弗兰克 - 康登态通过（至少）两个中间态弛豫。这些态通过瞬态光谱进行表征，并且反应途径通过量子化学计算进行建模。计算和测量的红外数据的比较表明，三重态介导的异构化途径是激发态慢动力学的原因。三重态通过由明亮的ππ态超快内转换产生的近简并nπ态的耦合而迅速填充。这种意外的异构化途径对若丹宁光开关的合成、分析和应用具有重要意义。
