Zhao Guijie, Shi Wei, Yang Yunfan, Ding Yong, Li Yongqing
School of Physics, Liaoning University, Shenyang 110036, P. R. China.
Key Laboratory for Microstructural Material Physics of Hebei Province, School of Science, Yanshan University, Qinhuangdao 066004, P. R. China.
J Phys Chem A. 2021 Apr 8;125(13):2743-2750. doi: 10.1021/acs.jpca.0c10799. Epub 2021 Mar 29.
Different substituents and benzene ring numbers had significant effects on the fluorescence phenomenon of 2-aryloxazoline derivatives as observed in an experiment. Here, we select five 2-aryloxazoline derivatives with different substituents and benzene ring numbers (2u, 2ad, 2af, 2ai, and 2ah) to analyze the effects on the fluorescence phenomena. For 2ad, 2ah, and 2ai, first, the geometric structures are optimized based on the density functional theory and time-dependent density functional theory methods. The analysis of the obtained bond parameters reveals the variation of hydrogen bond interactions from S to S states. Second, the calculated absorption and emission spectra are consistent with the experimental values, which proves that the theoretical method is feasible. Finally, through the analysis of the infrared vibrational spectrum, reduced density gradient isosurfaces, frontier molecular orbitals, and potential energy curves, the strengthening mechanism of the hydrogen bond interaction and the ability of the excited-state intramolecular proton transfer (ESIPT) reaction to occur are further explained. Since the proton transfer reactions of 2u and 2af occur spontaneously under photoexcitation, they have no stable structures in the S state. In conclusion, due to the different substituents, 2u is more prone to the proton transfer reaction than 2ad. For 2af, 2ai, and 2ah with different benzene ring numbers, the ESIPT reaction is more difficult to occur as the number of benzene rings increases. The ability of the ESIPT reaction to occur follows the order 2af → 2ah → 2ai. For 2-aryloxazoline derivatives with different substituents or different benzene ring numbers, the hydrogen bond strengthening mechanism has been authenticated, which promotes the occurrence of the ESIPT reactions.
实验观察发现，不同的取代基和苯环数目对2-芳基恶唑啉衍生物的荧光现象有显著影响。在此，我们选取了五种具有不同取代基和苯环数目的2-芳基恶唑啉衍生物（2u、2ad、2af、2ai和2ah）来分析其对荧光现象的影响。对于2ad、2ah和2ai，首先基于密度泛函理论和含时密度泛函理论方法对其几何结构进行优化。对得到的键参数进行分析，揭示了从S态到S*态氢键相互作用的变化。其次，计算得到的吸收光谱和发射光谱与实验值一致，这证明了该理论方法是可行的。最后，通过对红外振动光谱、约化密度梯度等值面、前线分子轨道和势能曲线的分析，进一步解释了氢键相互作用的增强机制以及激发态分子内质子转移（ESIPT）反应发生的能力。由于2u和2af在光激发下质子转移反应自发发生，它们在S态没有稳定结构。总之，由于取代基不同，2u比2ad更容易发生质子转移反应。对于具有不同苯环数目的2af、2ai和2ah，随着苯环数目的增加，ESIPT反应越难发生。ESIPT反应发生的能力顺序为2af→2ah→2ai。对于具有不同取代基或不同苯环数目的2-芳基恶唑啉衍生物，氢键增强机制已得到证实，这促进了ESIPT反应的发生。
