Journal of Physical Chemistry A, Vol.102, No.23, 4256-4265, 1998
Vibronic and vibrational coherence and relaxation dynamics in the TCNE-HMB complex
In a previous paper, we have performed the molecular orbital calculation for the TCNE-HMB complex to find that there exist two charge-transfer (CT) states separated by only a few hundred wavenumbers, and based on this model, we have analyzed the steady-state absorption and fluorescence spectra. In this paper, we shall use this model to analyze the femtosecond fluorescence profiles reported by Rubtsov and Yoshihara and the femtosecond pump-probe time-resolved spectra reported by Wynne et al. For this purpose, vibrational relaxation, vibrational coherence, and electronic relaxation and vibronic coherence between the two CT states are considered. For the case of the TCNE-HMB complex in a nonpolar solvent, we find that the vibrational coherence is due to the 159-161.7 cm(-1) mode, which has a vibrational relaxation time of 0.1-0.2 ps. We also find that the interaction energy between the two CT states is 50-80 cm(-1), which leads to internal conversion from CT2 to CT1 and back electron transfer from the CT1 to the ground electronic state with a time constant of 11.2 ps.
Keywords:CHARGE-TRANSFER COMPLEX;DONOR-ACCEPTOR COMPLEX;OPTICAL TRANSMISSION-CORRELATION;PROBE STIMULATED-EMISSION;RESONANCE RAMAN-SPECTRA;ELECTRON-TRANSFER;QUANTUM BEATS;HEXAMETHYLBENZENE;TETRACYANOETHYLENE;SPECTROSCOPY