Adiabatic structural relaxation in heterocyclic nitrogen-containing cations - The structure, absorption and fluorescence of the 2,4,6-triarylsubstituted pyridinium cations

The detailed studies of the 2,4,6-(N-alkyl)triarylsubstituted pyridinium ca tions I as well as the large series of the model structures have been carri ed out by absorption, fluorescent and polarization methods in the solvents of various polarity and viscosity at different temperatures. The localizati ons of the lowest electron transitions are determined. It is shown that the fluorescence with anomalous Stokes shift (ASS-fluorescence) arises owing t o the adiabatic structural relaxation (ASR) with the formation of the flatt ened (but not twisted) structure. The advantages of I as the objects for AS R study are discussed. The crude determination of the ASR kinetic parameter s has been conducted. A data assume that the ASS fluorescence quantum yield s of the cations I are conditioned mainly by deactivation processes in the final flattened structure. (C) 1998 Elsevier Science S.A. All rights reserv ed.