Quenching of Excited Singlet and Triplet States of Some Polyfused Arenes by Dihalobenzenes

Abstract

Abstract External heavy atom effect on the emission spectra of naphthalene, phenanthrene, and chrysene by perturbers dihalobenzenes are investigated to estimate different nonradiative rate constants associated with the depletion of the singlet and the triplet states of the fluorescers. The bimolecular fluorescence quenching rate constant kq has been evaluated at 300 K by applying Stern–Volmer relation. The dihalobenzene quenchers have triplet states lying below the singlet states of the fluorescers and the overall quenching rate kq is composed of two rate constants, namely, the intramolecular intersystem crossing rate kqISC and the singlet–triplet energy transfer rate constant kqST. The relative magnitudes of the two rate constants kqISC and kqST have been examined in the light of the energy conditions controlling the associated processes. At 77 K, the phosphorescence decay curve of the fluorescers in the presence of dihalobenzenes is biexponential and the triplet decay of the perturbed fraction of the fluorescers is exponential. It is concluded that at the low temperature, heavy atom interaction in the systems studied mainly proceeds through CT mechanism. Speculative suggestion has been made to account for enhancement of phosphorescence emission of polyfused arenes in EtOH solution.