The fluorescence of some dipolar NN-dialkyl-4-(dichloro-1,3,5-triazinyl)anilines. Part 2. Temperature and solvent effects on the radiationless decay of an intramolecular charge-transfer excited singlet state

Abstract

The fluorescence of NN-diethyl-4-(2,6-dichloro-1,3,5-triazinyl)aniline is strongly quenched by solvents of even moderate polarity. Reduction of the electron acceptor character of the triazinyl ring system, by substitution of a dimethylamino-group for a chlorine atom, leads to a dramatic decrease in the susceptibility to fluorescence quenching by polar solvents.The quenching mode is ascribed to a solvent-assisted twist of the NN-diethylamino moiety in the intramolecular charge-transfer (ICT) excited singlet state to yield a twisted (TICT) biradicaloid zwitterionic singlet state. At low temperatures, in viscous media, this radiationless decay appears to be limited by the dielectric relaxation rate of the solvent.