Fluorescence spectroscopic studies have been performed on the radical cations of tetrathiafulvalene (TTF), 4,4′-dimethyl-5,5′-diphenyltetrathiafulvalene (DMDP–TTF), bis-(4,5-dihydronaphtho-[1,2d]-tetrathiafulvalene) (BDHN–TTF) and bis-(ethylenedithio)-tetrathiafulvalene (BEDT–TTF) in low-temperature organic glasses. For the first time emission and excitation spectra have been obtained for radical cations of this class of compounds. Only in the case of BEDT–TTF·+ fluorescence could not be detected. The luminescence spectra have been related to the corresponding UV/Vis/NIR absorption spectra and absorption data obtained using the LNDO/S PERTCI method. For DMDP–TTF·+ the fluorescence lifetime (1.09 ns) has been measured and the fluorescence quantum yield (5×10−3) has been estimated.

The fluorescence and fluorescence excitation spectra of the radical cation of 5,10-dihydro-5,10-dimethylphenazine (DHDMP⋅+) have been recorded in liquid solution at room temperature. The fluorescence lifetime (0.47 ns) has been measured in an organic glass at 77K and the fluorescence quantum yield (1×10−3) has been estimated. This is virtually the only organic radical cation for which all the above-mentioned photophysical properties have been obtained in an organic solvent and the only system for which the spectra are available at room temperature. This is due to the unusually high stability of the DHDMP⋅+ radical cation and is an important step forward with regard to practical applications using radical cations.