Cage effects upon light irradiation on azo compounds:: cis→trans isomerization in polymethyl methacrylate

Three azo compounds of different molecular sizes were used to study relation between the rates of trans-->cis photoisomerization and inverse isomerization in the dark in a polymethyl methacrylate matrix. Molecule distribution over isomerization rates is observed for both direct and inverse isomerizations. It is shown that correlation between the rates of trans-->cis photoisomerization and inverse dark isomerization takes place for compound of large molecular size: the molecules that are most quickly isomerized in the some direction are also quickly isomerized in the opposite direction. No correlation is recorded in case of small molecular size compound. These results are: explained by a change in local matrix structure due to light energy dissipation. (C) 1999 Elsevier Science S.A. All rights reserved.