Effect of Deuteration of Durene on the Lifetime of the Phosphorescent Triplet State of Naphthalene in a Durene Host Crystal

The observation of a pronounced increase in the lifetime of the lowest triplet state of naphthalene in a single crystal of durene produced by deuteration of the durene is reported. For naphthalene-d8 at ∼298°K the increase in mean life is from 0.8 to 10.8 sec. It is shown that the decay in question is an exponential triplet—singlet intramolecular transition.