Photoresponsive New Polysiloxanes with 4‐Substituted Azobenzene Side‐Groups. Synthesis, Characterization and Kinetics of the Reversible Trans‐Cis‐Trans Isomerization

New polydimethylsiloxanes with p-substituted azobenzene side-groups were synthesized. Thin films and solutions exhibit a photochemical trans-cis isomerization of the azobenzene groups, followed by their cis-trans thermal relaxation in the dark. In films, relaxation rates were found to be 100-1000 times slower than the rates of photoisomerization, the former being very sensitive to the electron-acceptor character of the substituents. in solution, the rates of cis-trans relaxation are lower than those obtained for the solid state. This is ascribed to the dipolar intramolecular interactions between cis chromophores, which are favored in solution.