Comparative study of spin–orbital coupling for halogenated ethylbenzenes by a study of thier fluorescence

Abstract

The effects introduced by a change in the distance separating a chromophore from a non-conjugated perturber upon the fluorescence quantum yield have been investigated. Substitution of a chlorine or bromine atom at either the α- or β-position in ethylbenzene led to a substantial reduction in the quantum yield of fluorescence of the hydrocarbon. The results obtained have been interpreted as providing a quantitative measure of the degree of orbital mixing between chromophore and perturber. The mechanism for the quenching reaction involved spin–orbital coupling and results implicating the involvement of an intermediate, excited state, charge transfer complex (exciplex) have been explained. A quantitative comparison of the fluorescence quenching exhibited by internal and external halogen atoms has been made.