Optical free induction decay of molecules undergoing radiative and radiationless relaxation

Abstract

In this paper we examine the effect of radiative and radiationless processes on optical free induction decay (OFID) in singlet–singlet transitions of molecules in the condensed phase. The main conclusion is that the applicability of OFID to molecular singlet–singlet transitions is severely limited by the presence of an intermediate triplet state, which quite often forms a bottleneck in the optical pumping cycle. Using the theoretically derived formulas for the OFID signal, we examine the feasibility of OFID experiments on the mixed crystals of porphin in n-octane and naphthalene in durene and conclude that such experiments, if at all fruitful, would be difficult to execute. We re-evaluate the reported OFID results of pentacene in p-terphenyl and obtain for the lowest 1B2u←1A1g transition a dipole moment of 0.9±0.3 D.