具有两性离子特性的分子在非线性光学中具有重要的利用潜力,光电子学,和有机激光器由于其大的偶极矩。最近,Sakai等人合成的化合物2,4-双(4,5-二苯基-1H-咪唑-2-基)苯酚(2,4-bImP)。因其在溶剂中的独特光致变色性能而受到关注[J.Phys.Chem.A,125(2021),4784-4792].在氯仿中观察到的荧光归因于酮互变异构体。基于激发态的分子内质子转移,氯仿中2,4-bImP的光致变色被解释为两性离子的产生。然而,具有特定电子结构的两性离子可以与常规中性结构共振。在先前的研究中没有考虑来自两性离子和常规中性结构的共振贡献对荧光属性的影响。在这次调查中,已经使用密度泛函理论和时间依赖性密度泛函理论探索了氯仿中2,4-bImP的ESIPT机理。优化的几何构型参数说明了分子共振性质。在优化结果的基础上计算的荧光光谱进一步证实,质子转移后的荧光峰源于两性离子和中性构型的共振。通过静电势和原子偶极修饰的Hesfeld原子电荷(ADCH)分析证明了分子的两性离子性质。此外,势能曲线和红外光谱的表征进一步验证了两性离子和中性结构的共振。结果表明,ESIPT后,2,4-bImP分子产生中性邻醌结构和两性离子结构共振现象。上述共振结构为荧光的归属提供了新的见解。这些发现为两性离子的探索和发展奠定了理论基础。
Molecules with zwitterionic characteristics exhibit significant potential for utilization in nonlinear optics, optoelectronics, and organic lasers owing to their large dipole moments. Recently, the synthesized compound 2,4-bis (4,5-diphenyl-1H-imidazol-2-yl) phenol (2,4-bImP) by Sakai et al. has been noticed for its unique photochromic properties in solvents [J. Phys. Chem. A, 125 (2021), 4784-4792]. The observed fluorescence in chloroform was attributed to the keto tautomer. Based on the excited state intramolecular proton transfer, the photochromism of 2,4-bImP in chloroform was interpreted as zwitterion production. However, the zwitterion with a specific electronic structure can be in
resonance with the conventional neutral structure. The impact of the
resonance contribution from the zwitterion and the conventional neutral structure on fluorescence attribution was not taken into account in the previous studies. In this investigation, the ESIPT mechanism of the 2,4-bImP in chloroform has been explored using both the density functional theory and the time-dependent density functional theory. The optimized geometric configuration parameters illustrate the molecular resonant properties. The calculated fluorescence spectra on the basis of the optimization results further corroborate that the fluorescence peaks after proton transfer originates from the resonance of the zwitterionic and the neutral configuration. The zwitterionic nature of the molecule was demonstrated by electrostatic potential and atomic dipole modified Hesfeld atomic charge (ADCH) analysis. Furthermore, the characterization of potential energy curves and IR spectrum further verified the
resonance of both the zwitterionic and neutral structures. The results reveal that the 2,4-bImP molecule generates the neutral o-quinoid structure and the zwitterionic structure
resonance phenomenon following ESIPT. The aforementioned
resonance structure offers novel insights into the ascription of fluorescence. These discoveries establish the theoretical foundation for the exploration and development of zwitterions.