ELECTRON DONOR-ACCEPTOR INTERACTIONS IN FLUORESCENT STATE OF TETRACYANOBENZENE-AROMATIC HYDROCARBON COMPLEXES

Electron donor-acceptor interactions in s-tetracyanobenzene and tetrachlorophthalic anhydride-aromatic hydrocarbon complexes in their lowest excited singlet state (lowest charge-transfer state) have been investigated by fluorescence measurements. The effects of temperature and solvent polarity on the wave numbers of fluorescence spectra, relative fluorescence quantum yields, and fluorescence decay times of the complexes clearly showed a considerable difference of the energies as well as the structures between the excited Franck-Condon state and equilibrium state which originated from the large difference between the electronic structures in the ground and excited state of the complex. The so-called “mirror-symmetry” relation between the absorption and fluorescence spectra did not hold for these complexes at higher temperature, although the fluorescence excitation spectra agreed exactly with the absorption spectra, respectively. Furthermore, the existence of a rather large solvent effect on the structure of the fluorescent state of the complex has been shown to be likely. © 1969, American Chemical Society. All rights reserved.