N-甲基吡咯-2-甲醛激发态结构动力学及其溶剂效应的共振拉曼光谱和密度泛函理论研究

Resonance Raman Spectroscopy and Density Functional Theory Investigations on the Excited State Structural Dynamics of N-Methylpyrrole-2-carboxaldehyde and Its Solvent Effect

获取了覆盖N-甲基吡咯-2-甲醛(NMPCA)A-带和B-带电子吸收共7个激发波长的共振拉曼光谱,并结合含时密度泛函理论(TD-DFT)方法研究了的A-带和B-带电子激发和Franck-Condon区域结构动力学.TD-B3LYP/6-311++G(d,p)计算表明:A-带和B-带电子吸收的跃迁主体为π→π*.共振拉曼光谱可以指认为,11-13振动模式(A-带激发)或者7-11振动模式(B-带激发)的基频、倍频和组合频,其中C=O伸缩振动(ν7)、环的变形振动+N1-C6伸缩振动(ν17)、环的变形振动(ν21)和C6-N1-C2/C2-C3-C4不对称伸缩振动(ν14)占据了绝大部分.这表明NMPCA的Sπ激发态结构动力学主要沿C=O伸缩振动、环的变形振动和环上N1-C6伸缩振动等反应坐标展开.在同一溶剂的共振拉曼光谱中随激发波长由长变短,ν7与ν14的强度比呈现出由强变弱再变强的现象,这种变化规律被认为与Franck-Condon区域Sn/Sπ态混合或势能面交叉有关.溶剂对Sn/Sπ态混合或势能面交叉具有调控作用.

Resonance Raman spectra of N-Methylpyrrole-2-carboxaldehyde （NMPCA） were obtained and seven excitations covered the A-and B-band electronic absorptions.The electronic excitations and the Franck-Condon region structural dynamics of NMPCA were studied by resonance Raman spectroscopy and time-dependent density functional theory （TD-DFT） calculations.The A-and B-band electronic absorptions were assigned to π→π transitions on the basis of the TD-B3LYP/6-311＋＋G（d,p） level of theory.The resonance Raman spectra showed Raman intensity in the fundamentals,the overtones and the combination bands for about 11-13 vibrational modes （A-band excitation） or 7-11 vibrational modes （B-band excitation）.These were predominately due to the C=O stretch mode ν7,the ring deformation＋N1-C6 stretch ν17,the ring deformation mode ν21 and the C6-N1-C2/C2-C3-C4 anti-symmetry stretch mode ν14.This indicates that the Franck-Condon region Sπ structural dynamics of NMPCA mainly occurs along the C=O stretch,the ring deformation,and the N1-C6 stretch reaction coordinates.In a certain solvent and under different excitation wavelengths the relative intensity of the C=O stretch mode ν7 versus the C6-N1-C2/C2-C3-C4 anti-symmetry stretch mode ν14 shows an intense to weak to intense change as the excitation wavelengths decrease.This intensity variation directly reflects the Sn/Sπ state-mixing or crossing of the potential energy surfaces in the Franck-Condon region.Solvents can efficiently tune the Franck-Condon region Sn/Sπ state-mixing or crossing processes.