The fluorescence of some dipolar NN-dialkyl-4-(dichloro-1,3,5-triazinyl)anilines. Part 1. Solvent effects and solvent exciplex formation

Abstract

The fluorescence emissions of the title compounds occur from highly charge-transfer excited states and, in cyclohexane solution, the fluorescence quantum yields ϕ_F are high. In aprotic solvents of low to moderate polarity ϕ_F is much reduced, mainly by an increase in the non-radiative rate constant k_NR with solvent polarity increase. The decay channel is thought to be intersystem crossing from the singlet to the triplet intramolecular charge transfer excited state. The formation of a 1 : 1 solvent exciplex between acetonitrile and the excited dipolar triazine system in aliphatic hydrocarbon solvents has been investigated and found to be diffusion controlled.