In the present work, the photoinduced charge-transfer (CT) behavior of 7-phenyl-6H-pyrido[1,2-a:3,4-b′]diindole-6,13(12H)-dione (HCB) as a function of solvent polarity is reported by UV–vis absorption, steady-state and time-resolved fluorescence, and quantum chemical calculations. Calculated excited state energies of HCB at the B3PW91/6-31+G* level in vacuo and in solvents fulfill the energy requirements for singlet fission, which is the most promising path for the generation of highly efficient solar cells. The calculated potential energy curve for the compound reveals that the keto form is the predominant form in the ground state. Large bathochromic shifts in fluorescence with decreasing trends of quantum yield and lifetime indicate the occurrence of intramolecular CT from the indole bicycle to the indolinone moiety of HCB in highly polar solvents. The observed quenching of HCB fluorescence in different solvents without altering the spectral shape upon addition of a donor, triethylamine, is attributed to intermolecular CT, and it was examined in terms of the Stern–Volmer kinetics. The thermodynamics of photoinduced CT processes in HCB was analyzed using the measured photophysical data and cyclic voltammetric redox potentials via the Rehm–Weller equation. Analyses with the semiclassical Marcus theory suggest that both the CT processes fall under the Marcus normal region.

中文翻译：

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单环靛蓝的光物理学：分子内和分子间电荷转移

在本工作中，7-苯基-6 H -pyrido[1,2- a :3,4- b ']diindole-6,13(12 H )-dione ( HCB)的光致电荷转移（CT）行为）作为溶剂极性的函数，通过紫外可见吸收、稳态和时间分辨荧光以及量子化学计算来报告。计算得出的HCB在真空和溶剂中 B3PW91/6-31+G* 能级的激发态能量满足单线态裂变的能量要求，这是产生高效太阳能电池的最有希望的途径。计算出的化合物势能曲线表明，酮形式是基态的主要形式。荧光的大红移以及量子产率和寿命下降的趋势表明在高极性溶剂中从吲哚自行车到HCB的吲哚酮部分发生分子内 CT 。在添加供体三乙胺后，在不同溶剂中观察到的HCB荧光猝灭而不改变光谱形状，这归因于分子间 CT，并根据 Stern-Volmer 动力学进行了检查。利用测得的光物理数据和循环伏安氧化还原电位通过 Rehm-Weller 方程分析了HCB中光致 CT 过程的热力学。半经典 Marcus 理论的分析表明，两个 CT 过程都属于 Marcus 正常区域。