Light-induced adiabatic structural relaxation and electronic energy deactivation in Pyridinium bications

The comparative detailed investigation of the Bication pyridinium systems ( BCP) and corresponding model pyridinium cations (CP) has been carried out b y the spectral luminescent methods. BCP consist of the two identical moieti es bound by the various space bridges ensuring their very weak interaction in the ground state. The Adiabatic Structural Relaxation (ASR) followed by the photocyclization reaction is realized only in one of BCP fragments in a ccordance with the general scheme typical for CP. The ASR is not realized i n another BCP fragment owing to the S-1 state deactivation by the extremely fast Interfragmental Intramolecular S-S Energy Transfer from the unchanged fragment to the cyclized one. The ASR mechanism, luminescent properties an d photoproduct structures depend strongly on the solvent temperature (visco sity) and on the steric interactions typical for the BCP. The additional in formation concerning the N phenyl role in the fluorescence and photo-chemic al properties' formation in CP has been obtained by the study of the BCP. ( C) 2000 Elsevier Science S.A. All rights reserved.