Charge-Transfer Interaction and Fluorescence in Some Tetracyanobenzene Complexes

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Abstract
Fluorescence lifetimes and quantum yields were measured for some tetracyanobenzene complexes with benzene and its methyl derivatives, and the radiative and nonradiative rate constants were determined under various conditions. The results show that the low fluorescence intensities of the complexes in nonpolar fluid media are due to small radiative rate constants and that nonradiative processes become important for the complexes in polar fluid media. From the theoretical consideration of the observed radiative transition probability, it is found that the geometry and the charge distribution in the excited equilibrium state are greatly different from those in the excited Franck-Condon state for the complexes in fluid media at room temperature and that the degree of the charge-transfer in the former state amounts to 96–100%, while it is only 12–45% in the latter state. The stabilization energy due to the reorientation was obtained from the temperature dependence of the fluorescence spectrum.