Radiationless Triplet—Singlet Transitions in Naphthalene

The fluorescent intensity, phosphorescent intensity, and phosphorescent lifetime of naphthalene and naphthalene-ds, dissolved in durene, were measured as a function of temperature from 77° to 325°K. These measurements indicate that radiationless transitions from the first excited singlet state are temperature-independent but radiationless transitions from the lowest triplet are strongly temperature-dependent. Analysis of the data for the decay of the triplet state indicates that only one activated state is responsible for this temperature dependence. The activation energy and pre-exponential factor for decay from this state are 3559±79 cm—1 and (4.2±1.5)×107 sec—1 for naphthalene, and 3362±35 cm—1 and (1.30±0.24)×107 sec—1 for naphthalene-ds. These data can be interpreted as corresponding to the excitation of one of the intramolecular CC stretching modes to its second excited state or a combination of two CC fundamentals.