SOLVENT EFFECTS ON THE FLUORESCENCE QUENCHING RATE-CONSTANT OF AN INTRAMOLECULAR EXCIPLEX BY POLY(CHLOROBENZENES)

The fluorescence of the intramolecular exciplex formed by N,N-diethyl- 2-(1-naphthyl)ethylamine (I), was quenched by chlorobenzenes in aceton itrile, tetrahydrofuran, ethylacetate and cyclohexane. An electron tra nsfer mechanism was proposed for the quenching process. It was observe d that the second-order quenching rate constants, when the process is not diffusionally controlled, markedly increase as the relative permit tivity of the solvent decreases. This unusual behaviour is analysed in terms of the Marcus theory of electron transfer reactions. It is sugg ested that the increase in the rate with decreasing solvent polarity m ay be explained by a lowering of the solvent barrier.