Photochemical isomerization of thioindigo derivatives embedded in poly(methyl methacrylate)

Photoisomerization of a number of thioindigo derivatives dissolved in butyl acetate or embedded in glassy poly(methyl methacrylate) (PMMA) has been investigated between 290 and 385 K. Trans-cis isomerization is inhibited in the glassy polymer while the quantum yield of the cis-trans transition is unaffected. The results have been interpreted from the point of view of increased molar volume in trans-cis isomerization. The absolute values of ΔV were obtained by comparing the activation energy Ea of isomerization in PMMA with activation energies characterizing diffusion of gases with different van der Waals dimensions in the polymer. Isomerization which involves singlet excimers in inhibited by the polymer to a higher degree than isomerization with participation of the long-lived triplet states.