Luminescence of 5-Phenyltetrazole and its Derivatives. Part II. Phosphorescence

The phosphorescence spectra, mean lifetimes of phosphorescence and ratios of phosphorescence/fluorescence quantum yields have been measured for 5-phenyitetrazole and its three methyl derivatives in a polyvinyl alcohol film over the temperature range of (77−250) K. Temperature responses of the non-radiative intersystem crossing constant. KST, and the non-radiative triplet state deactivation constant. km, have been investigated on the basis of these measurements. The energy of activation for the non-radiative transitions has been determined. With the methyl 5-phenyltetrazoles. the thermal deactivation of the triplet state, contrary to the intersystem crossing, has been found to be influenced by the position of the methyl substituent in the phenyl ring.