Acta Phys. -Chim. Sin. ›› 2012, Vol. 28 ›› Issue (01): 65-72.doi: 10.3866/PKU.WHXB20122865


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

XU Zong-Ping, ZHAO Yan-Ying, WANG Hui-Gang, ZHENG Xu-Ming   

  1. Key Laboratory of Advanced Textiles Materials and Manufacture Technology, and Engineering Research Center for Eco-dyeing and Finishing of Textiles, Ministry of Education, Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou 310018, P. R. China
  • Received:2011-08-30 Revised:2011-10-15 Published:2011-12-29
  • Contact: ZHENG Xu-Ming
  • Supported by:

    The project was supported by the National Key Basic Research Program of China (2007CB815203), National Natural Science Foundation of China (21033002, 20803066), and Natural Science Foundation of Zhejiang Province, China (Y4090161).

Abstract: 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 ππ* 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.

Key words: N-Methylpyrrole-2-carboxaldehyde, Excited state structural dynamics, Resonance Raman spectrum, Solvent effect


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