Structural Dynamics of 3-Dimethylamino-2-methyl-propenal in S2(ππ*)State (cited: 3)
- Received Date: 2013-11-23
- Structural dynamics, Conical intersection, Excited state, Resonance Raman, CASSCF calculation
Abstract: The photophysics of 3-dimethylamino-2-methyl-propenal (DMAMP) after excitation to the S2(ππ*) electronic state was studied using the resonance Raman spectroscopy and complete active space self-consistent field method calculations. The transition barriers of the ground state tautomerization reactions between DMAMP and its three isomers were determined at B3LYP/6-311++G(d,p) level of theory. The vibrational spectra were assigned. The A-band resonance Raman spectra were obtained in acetonitrile with excitation wavelengths in resonance with the first intense absorption band to probe the structural dynamics of DMAMP. The B3LYP-TD computation was carried out to determine the relative A-band resonance Raman intensities of the fundamental modes, and the result indicated that the vibronic-coupling existed in Franck-Condon region. Complete active space self-consistent field (CASSCF) calculations were carried out to determine the excitation energies of the lower-lying singlet and triplet excited states, the conical intersection points and the inter-system crossing points. The A-band short-time structural dynamics and the corresponding decay dynamics of DMAMP were obtained by analysis of the resonance Raman intensity pattern and CASSCF computations. It was found that a sudden de-conjugation between C1=O6 and C2=C3 occurred at the Franck-Condon region of the S2(ππ*) state, while the enhancement of the conjugation interaction between C3 and N(CH3)2, and between C1 and C2 evolutions shortly after the wavepacket leaves away the Franck-Condon region via the excited state charge redistribution. The de-conjugation interaction between C1=O6 and C2=C3 made the rotation of C3=N(CH3)2 group around the C2-C3 bond much easier, while the enhanced conjugation between C1 and C2, and between C3 and N(CH3)2 made the rotation around the C1-C2 bond and C3-N5 more difficult. It was revealed that the initial structural dynamics of DMAMP was predominantly towards the CI-1(S2/S0) point, while the opportunities towards either CI-2(S2/S0) or CI-3(S2/S0) point were negligible. Two decay channels of DMAMP from S2,FC(ππ*) to S0 or T1,min via various CIs and ISCs were proposed.
|Citation:||Sheng Pan, Jia-Dan Xue, Xu-ming Zheng. Structural Dynamics of 3-Dimethylamino-2-methyl-propenal in S2(ππ*)State (cited: 3)[J]. Chinese Journal of Chemical Physics , 2014, 27(2): 149-158. doi: 10.1063/1674-0068/27/02/149-158|