Fluorescence of some dipolar N,N-disubstituted 4-(dichloro-1,3,5-triazinyl)anilines. Part 4. Internal and molecular rotations in homogeneous and inhomogeneous media

Abstract

Radiative and non-radiative decay constants have been obtained for the N,N-diethyl and N,N-diphenyl derivatives of the title compounds (DETA and DPTA, respectively). DETA fluorescence occurs from a planar conjugated excited singlet state which decays by an internal rotation about the anilino nitrogen–carbon bond at a rate close to the polar solvent dielectric relaxation rate By contrast, the detectable emission from DPTA is from a twisted species, and its decay is an order of magnitude slower than that of the DETA emission.

The molecular tumbling of the DPTA molecules in homogenous solvents is deduced to be isotropic. Preliminary studies on the applicablity of the triazine dyes as fluorescence probes are reported. In aqueous neutral or alkaline media the dyes undergo hydrolysis but the product fluorescence can be utilised Hydrolysed DPTA probe rotation in egg lecithin unilamellar vesicles is probably isotropic and has an activiation barrier of 26 kJ mol^–1 in the liquid crystalline phase.

DPTA dye is adsorbed strongly onto porous Vycor glass but the fluorescence emission is complex.