Yu Xiangrui, Shang Changjiao, Cao Yunjian, Cui Jingang, Sun Chaofan
College of Science, Northeast Forestry University, Harbin 150040, China.
Materials (Basel). 2022 Apr 15;15(8):2896. doi: 10.3390/ma15082896.
To reveal the influence of different substituents on the excited-state intramolecular proton transfer (ESIPT) process and photophysical properties of 4′-N, N-dimethylamino-3-hydroxyflavone (DMA3HF), two novel molecules (DMA3HF-CN and DMA3HF-NH2) were designed by introducing the classical electron-withdrawing group cyano (-CN) and electron-donating group amino (-NH2). The three molecules in the acetonitrile phase were systematically researched by applying the density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. The excited-state hydrogen bond enhancement mechanism was confirmed, and the hydrogen bond intensity followed the decreasing order of DMA3HF-NH2 > DMA3HF > DMA3HF-CN, which can be explained at the electronic level by natural bond orbital, fuzzy bond order, and frontier molecular orbital analyses. Moreover, we found from the electronic spectra that the fluorescence intensity of the three molecules in keto form is relatively strong. Moreover, the calculated absorption properties indicated that introducing the electron-withdrawing group -CN could significantly improve the absorption of DMA3HF in the ultraviolet band. In summary, the introduction of an electron-donating group -NH2 can promote the ESIPT reaction of DMA3HF, without changing the photophysical properties, while introducing the electron-withdrawing group -CN can greatly improve the absorption of DMA3HF in the ultraviolet band, but hinders the occurrence of the ESIPT reaction.
为揭示不同取代基对4′-N，N-二甲基氨基-3-羟基黄酮（DMA3HF）的激发态分子内质子转移（ESIPT）过程和光物理性质的影响，通过引入经典的吸电子基团氰基（-CN）和供电子基团氨基（-NH2）设计了两个新型分子（DMA3HF-CN和DMA3HF-NH2）。采用密度泛函理论（DFT）和含时密度泛函理论（TD-DFT）方法对乙腈相中的这三种分子进行了系统研究。证实了激发态氢键增强机制，氢键强度遵循DMA3HF-NH2>DMA3HF>DMA3HF-CN的递减顺序，这可以通过自然键轨道、模糊键级和前线分子轨道分析在电子层面进行解释。此外，我们从电子光谱中发现，三种分子酮式的荧光强度相对较强。而且，计算得到的吸收性质表明，引入吸电子基团-CN可显著提高DMA3HF在紫外波段的吸收。综上所述，引入供电子基团-NH2可促进DMA3HF的ESIPT反应，且不改变其光物理性质，而引入吸电子基团-CN可大幅提高DMA3HF在紫外波段的吸收，但会阻碍ESIPT反应的发生。
