Photophysical decay processes of toluene in dilute solution

Fluorescence yields, fluorescence lifetimes and triplet yields have been measured for dilute solutions of toluene in methylcyclohexane over the temperature range 213 to 333 K. Fluorescence and intersystem crossing for this system are independent of temperature and a radiationless S1→ S0 decay occurs by a single temperature dependent process. The rate constant for this latter process has an activation energy of 0.17 eV and an A factor of 8 × 109 s–1. The data are compared with those for benzene. The differences are explained on the basis of the effect of methyl substitution on the energy and symmetry of aromatic ring.