ABSORPTION, FLUORESCENCE, AND RESONANCE RAMAN-SPECTROSCOPY OF THE HEXAMETHYLBENZENE TETRACYANOETHYLENE CHARGE-TRANSFER COMPLEX - TOWARD A SELF-CONSISTENT MODEL
K. Kulinowski et al., ABSORPTION, FLUORESCENCE, AND RESONANCE RAMAN-SPECTROSCOPY OF THE HEXAMETHYLBENZENE TETRACYANOETHYLENE CHARGE-TRANSFER COMPLEX - TOWARD A SELF-CONSISTENT MODEL, Journal of physical chemistry, 99(22), 1995, pp. 9017-9026
The weak, far-red fluorescence spectrum of the hexamethylbenzene/tetra
cyanoethylene charge-transfer complex has been measured in CCl4 and cy
clohexane solvents. The total fluorescence quantum yield in CCl4 with
633 nm excitation is about 5 x 10(-5). The absorption spectrum, absolu
te resonance Raman excitation profiles, and fluorescence spectrum in C
Cl4 are simulated with a common model that explicitly includes the 11
most strongly Franck-Condon-active internal vibrations as Well as the
solvent, treated as an overdamped Brownian oscillator. The fits to the
data require a large (2450 cm(-1)) ''solvent'' reorganization energy,
which may involve a combination of true solvent motions and very low-
frequency intermolecular complex vibrations. The same model is used to
calculate the nonphotochemical return electron-transfer rate and comp
ared with previous measurements of the ion-pair lifetime. This represe
nts the first time, to our knowledge, that all four pieces of data (ab
sorption, fluorescence, Raman, and electron-transfer rate) have been s
imulated with a common model and compared with experimental results.