2-乙酰基-1-甲基吡咯激发态结构动力学及溶剂效应的共振拉曼光谱和密度泛函理论计算

获取了覆盖紫外光谱中A带和B带吸收的共7个不同激发波长的共振拉曼光谱, 并结合密度泛函理论方法研究了2-乙酰基-1-甲基吡咯(2-Ac-NMP)的A带和B带电子激发和Franck-Condon区域结构动力学. 在TD-B3LYP/6-311++G(d,p)计算水平上, A带和B带吸收的跃迁主体为π→π^* . A带和B带共振拉曼光谱分别指认为13个振动模式和8个振动模式的基频、泛频和组合频, 其中C＝O伸缩振动(ν₈)、C3-C4-C5不对称伸缩振动+C2-C6伸缩振动(ν₁₄)及环上CH面内摇摆(ν₁₈)对拉曼光谱强度贡献最大, 表明2-Ac-NMP的S_π激发态结构动力学主要沿反应坐标展开. 考察了溶剂对共振拉曼光谱强度模式的影响, 结果表明, 在同一溶剂中, 随激发波长由长变短, C＝O伸缩振动模(ν₈)的强度呈现出由强变弱再变强的现象. 这种变化规律与Franck-Condon区域S_n/S_π态混合或势能面交叉相关, 并受溶剂的有效调控.

Resonance Raman Spectroscopic and Density Functional Theory Investigations of Excited State Structural Dynamics of 2-Acetyl-1-methylpyrrole (2-Ac-NMP) and Its Solvent Effect

Resonance Raman spectra of 2-acetyl-1-methylpyrrole(2-Ac-NMP) were obtained with seven excitations covering the A-and B-band absorptions of the UV spectra.The electronic excitations and the Franck-Condon region structural dynamics of 2-Ac-NMP were studied with the resonance Raman spectroscopy and density functional theory calculations.The A-and B-band absorptions are assigned as the π→π* transitions on the basis of the TD-B3LYP/6-311++G(d,p) level of theory computations.The resonance Raman spectra displayed the Raman intensity in the fundamentals,overtones and combination bands of about 13 vibrational modes(for A-band) or 8 vibrational modes(for B-band),predominately in the C-O stretch mode(ν8),C3—C4—C5 anti-sym.stretch+C2—C6 stretch(ν14) and ring CH in-plane bend(ν18).This indicates that the Franck-Condon region Sπ structural dynamics of 2-Ac-NMP is mainly along the C-O stretch and ring defor-mation and ring CH in-plane bend coordinates.In a certain solvent and under different excitation wavelengths,the relative intensity of the ν8 versus the ν14 displays an interesting change that is from intense to weak and then to intense again as the excitation wavelengths goes from longer to shorter.This intensity variation directly reflects the Sn/Sπ state-mixing or curve-crossing in Franck-Condon region.Solvents can efficiently tune the Franck-Condon region Sn/Sπ state-mixing or curve-crossing processes.