PHOTOCHEMISTRY IN POLYMER SOLIDS .11. THE EFFECTS OF THE SIZE OF REACTION GROUPS AND THE MODE OF PHOTOISOMERIZATION ON PHOTOCHROMIC REACTIONS IN POLYCARBONATE FILM

The trans to cis photoisomerization and cis to trans thermal isomerization of 9,9'-azophenanthrene and stilbene molecularly dispersed in polycarbonate films were measured in the wide temperature range, from liquid helium temperature to 373 K. The final cis fraction for 9,9'-azophenanthrene is similar to that for 1,1'-azonaphthalene. The final cis fraction for stilbene in a film at room temperature reaches photoequilibrium similar to the case of azobenzene, but at low temperatures the final cis fraction for stilbene becomes lower than that for azobenzene. These facts suggest that these azo compounds isomerize via an inversion mechanism that requires a smaller sweeping volume than the rotation mechanism for stilbene. The results of a simulation according to a kinetic model considering the influences of the free volume distribution and its local fluctuation on the reactivity were given in order to explain the non-first-order reaction profile of trans to cis photoisomerization of 9,9'-azophenanthrene and stilbene and their temperature dependences.