Hu Mingxia, Jia Yanrong, Ni Qinghu, Li Yu, Zhu Jingtao, Zhao Yanying
Zhejiang Sci-Tech University, Hangzhou 310018, China.
Zhejiang Sci-Tech University, Hangzhou 310018, China.
Spectrochim Acta A Mol Biomol Spectrosc. 2025 Mar 15;329:125607. doi: 10.1016/j.saa.2024.125607. Epub 2024 Dec 16.
Excited-state intramolecular proton transfer (ESIPT) reactions are one of the fundamental energy transformation reactions in catalysis and biological process. The combining ESIPT with the twisted intramolecular charge transfer (TICT) brings the richness of optical, photoelectronic performances to certain functional compounds. Delineating the mechanism of ESIPT + TICT reactions and further understanding why a specific functional group dominates are fundamentally crucial for the design and application of the functionally photoelectric materials. In this paper, six 2-(2'-hydroxyphenyl) benzimidazole (HBIgens) derivatives involved in ESIPT + TICT were investigated by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations to have an insight into the photophysical and photochemical process in acetonitrile. The optimized geometries indicated that the intramolecular hydrogen bonds (-O-H···N-) were enhanced in the corresponding first singlet, which provided the fundamentally outstanding prerequisites of the ESIPT reactions. By further charge analysis, it is indicated that the introduction of substitutes to the different positions would determine the Stokes' shifts, and the electron-adopting p-cyanophenyl group mainly contributed to the TICT structure. Constraint scanning the potential energy curves of both ground and first singlet excited states, the electron-adopting N,N-diethylamino group on the meta position could enhance the barrier and inhibit the ESIPT reaction. Furthermore, the nucleus independent chemical shift (NICS(1)_ZZ) values of phenol groups indicate the relationship between the reversal aromaticity and the barrier of ESIPT, both of which were proved to be negatively correlated in the ESIPT reaction. It is concluded that not only both types and positions of substituents can tune the excited-state proton transfer behaviors in HBIgen derivatives, but also the aromatic rule can easily be applied to elaborate the ESIPT reaction.
激发态分子内质子转移（ESIPT）反应是催化和生物过程中基本的能量转换反应之一。将ESIPT与扭曲分子内电荷转移（TICT）相结合，为某些功能化合物带来了丰富的光学和光电性能。阐明ESIPT + TICT反应的机理，并进一步理解为何特定官能团起主导作用，对于功能光电材料的设计和应用至关重要。本文通过密度泛函理论（DFT）和含时密度泛函理论（TD-DFT）计算，研究了六种参与ESIPT + TICT的2-(2'-羟基苯基)苯并咪唑（HBIgens）衍生物，以深入了解乙腈中的光物理和光化学过程。优化后的几何结构表明，相应的第一单线态中分子内氢键（-O-H···N-）增强，这为ESIPT反应提供了根本上优异的前提条件。通过进一步的电荷分析表明，在不同位置引入取代基会决定斯托克斯位移，吸电子的对氰基苯基主要促成TICT结构。通过约束扫描基态和第一单线态激发态的势能曲线，间位上的吸电子N,N-二乙氨基会增加势垒并抑制ESIPT反应。此外，酚羟基的核独立化学位移（NICS(1)_ZZ）值表明了反芳香性与ESIPT势垒之间的关系，在ESIPT反应中二者被证明呈负相关。得出的结论是，不仅取代基的类型和位置可以调节HBIgen衍生物中的激发态质子转移行为，而且芳香性规则也可轻松用于阐述ESIPT反应。
