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

doi:10.3969/j.issn.0251-0790.2012.04.023

Abstract

Abstract: 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 S_π 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 S_n/S_π state-mixing or curve-crossing in Franck-Condon region. Solvents can efficiently tune the Franck-Condon region S_n/S_π state-mixing or curve-crossing processes.

Key words: 2-Acetyl-1-methylpyrrole(2-Ac-NMP), Excited state structural dynamics, Resonance Raman spectrum, Solvent effect

CLC Number:

O641

TrendMD:

XU Zong-Ping, ZHAO Yan-Ying, WANG Hui-Gang, ZHENG Xu-Ming. 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[J]. Chem. J. Chinese Universities, 2012, 33(04): 772.

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