摘要
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.
出处
《物理化学学报》
SCIE
CAS
CSCD
北大核心
2012年第1期65-72,共8页
Acta Physico-Chimica Sinica
基金
国家重点基础研究发展规划(2007CB815203)
国家自然科学基金(21033002,20803066)
浙江省自然科学基金(Y4090161)资助项目~~