Radiationless Triplet—Singlet Transitions in Naphthalene

Abstract

The fluorescent intensity, phosphorescent intensity, and phosphorescent lifetime of naphthalene and naphthalene‐d_s, 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‐d_s. 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.