Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Santo André, São Paulo 5001, Brazil.
Molecules. 2018 May 21;23(5):1231. doi: 10.3390/molecules23051231.
Excited state intramolecular proton transfer (ESIPT) is a photoinduced process strongly associated to hydrogen bonding within a molecular framework. In this manuscript, we computed potential energy data using Time Dependent Density Functional Theory (TDDFT) for triphenyl-substituted heterocycles, which evidenced an energetically favorable proton transfer on the excited state (i.e., ESIPT) but not on the ground state. Moreover, we describe how changes on heterocyclic functionalities, based on imidazole, oxazole, and thiazole systems, affect the ESIPT process that converts an enolic species to a ketonic one through photon-induced proton transfer. Structural and photophysical data were obtained theoretically by means of density functional theory (DFT) calculations and contrasted for the three heterocyclics. Different functionals were used, but B3LYP was the one that adequately predicted absorption data. It was observed that the intramolecular hydrogen bond is strengthened in the excited state, supporting the occurrence of ESIPT. Finally, it was observed that, with the formation of the excited state, there is a decrease in electronic density at the oxygen atom that acts as proton donor, while there is a substantial increase in the corresponding density at the nitrogen atom that serves as proton acceptor, thus, indicating that proton transfer is indeed favored after photon absorption.
激发态分子内质子转移（ESIPT）是与分子框架内氢键强烈相关的光诱导过程。在本文中，我们使用含时密度泛函理论（TDDFT）计算了三苯基取代杂环的势能数据，结果表明激发态（即 ESIPT）上质子转移具有能量优势，但在基态上则不然。此外，我们描述了杂环官能团的变化（基于咪唑、恶唑和噻唑体系）如何影响 ESIPT 过程，该过程通过光诱导质子转移将烯醇物种转化为酮型物种。通过密度泛函理论（DFT）计算获得了理论结构和光物理数据，并对三种杂环进行了对比。使用了不同的泛函，但 B3LYP 是能够充分预测吸收数据的泛函。结果表明，在激发态下分子内氢键得到加强，支持 ESIPT 的发生。最后，我们观察到，在形成激发态时，作为质子供体的氧原子上的电子密度降低，而作为质子受体的氮原子上的相应密度显著增加，这表明在吸收光子后，质子转移确实是有利的。
