In this work, we mainly focus on elaborating the effects of solvent polarity on excited state interactions and intramolecular proton transfer (ESIPT) behavior for the novel dye 2-(2-hydroxyphenyl) benzothiazole-5-(9H-carbazol-9-yl)phenol (HBT-Cz). Six aprotic solvents with different polarities are considered. Via comparing geometrical parameters, infrared (IR) vibrational spectra, and atomic charge distributions, we confirm that the hydrogen bond of HBT-Cz is enhanced in S₁ state. The enhancement of hydrogen bonding with low polarity is particularly important. Via exploring molecular orbitals, we find that intramolecular charge transfer happens and charge redistribution facilitates ESIPT reaction. Results show that low solvent polarity is more conducive to ESIPT process for HBT-Cz. In order to clarify detailed reaction mechanism, we construct potential energy curves and determine that the ESIPT process of HBT-Cz fluorophores could be controlled by solvent polarity. We not only elucidate the excited state behavior of HBT-Cz systems but also present the polarity-dependent ESIPT mechanism for HBT-Cz fluorophore.

中文翻译：

---

2-(2-羟基苯基) 苯并噻唑-5-(9H-咔唑-9-基) 苯酚荧光团的溶剂极性依赖性激发态行为：理论研究

在这项工作中，我们主要着重阐述溶剂极性对新型染料 2-(2-hydroxyphenyl) benzothiazole-5-(9H-carbazol-9-yl) 的激发态相互作用和分子内质子转移 (ESIPT) 行为的影响苯酚（HBT-Cz）。考虑了六种具有不同极性的非质子溶剂。通过比较几何参数、红外 (IR) 振动光谱和原子电荷分布，我们确认 HBT-Cz 的氢键在 S _1中增强状态。低极性氢键的增强尤为重要。通过探索分子轨道，我们发现发生分子内电荷转移和电荷重新分布促进了 ESIPT 反应。结果表明，低溶剂极性更有利于 HBT-Cz 的 ESIPT 过程。为了阐明详细的反应机理，我们构建了势能曲线并确定 HBT-Cz 荧光团的 ESIPT 过程可以通过溶剂极性控制。我们不仅阐明了 HBT-Cz 系统的激发态行为，而且还介绍了 HBT-Cz 荧光团的极性依赖性 ESIPT 机制。