Poly(azoaromatic viologen): its synthesis and reversibly photocontrollablesupramolecular assembly in a polymer/low-molar-mass system

Poly(azoaromatic viologen) (PAV) having both photoisomerizable azobenzene c hromophore and complexable bipyridinium unit in the backbone of the polymer chain was synthesized in an attempt to construct reversibly photo-induced, supramolecular assembling, polymer/low-molar-mass systems. It was found th at PAV could form 1/1 intermolecular complex with Eosin Y (EY) dye and the interactions between PAV and EY changed reversibly by light-irradiation. Th e conductivity of the solution decreased after complexation. PAV solution i rradiated with ultraviolet light (lambda(max) = 365 nm) showed an increase in conductivity. PAV exhibited a slightly larger trend to bind with EY unde r ultraviolet irradiation than that in the dark. PAV changed its conformati on under irradiation with ultraviolet light from trans form to cia form, an d recovered from cia form to trans form when it was kept in the dark again. The complex association constant (Ka) between the Cis-PAV(2n+) and EY2- wa s larger than that between the trans-PAV(2n+) and EY2-. PAV displayed a pho to-stimulated "on-off" binding with EY. The reversibly photo-induced change of properties of the complex solution has been explained by isomerization- diffusion mechanism. (C) 2000 Published by Elsevier Science S.A. All rights reserved.