The environmentally controlled photoisomerization of probe molecules containing azobenzene moieties in solid poly(methyl methacrylate)

Upon n → π* (436 nm) excitation of azobenzene probes 1, 2 and 3 in a solid film of poly(methyl methacrylate) we observe cis‐trans isomerization and a monoexponential approach towards the photostationary state; upon π → π* (313 nm) irradiation this approach is bi‐exponential. The latter is not due to the loss of concentration homogeneity during the reaction. By transferring the concept of dual isomerization mechanisms (rotation and inversion) from former work we reinterpret the “fast” component of isomerization at 313 nm excitation as being due to rigidly held molecules unable to isomerize via the rotation mechanism, but undergoing internal conversion and subsequent inversion, and the “slow” component as being due to molecules isomerizing by rotation. On 436 nm irradiation only one isomerization mechanism is active, viz. inversion.