Polymethacrylates with benzylidenephthalimidine side chains, 1. Photochemical characteristics of model compounds and polymers

The photochemical behavior of polymers with benzylidenephthalimidine (BPI) side chains is described, together with the photochemistry of low-molecular BPIs in solution. The stereochemistry of BPIs is critically influenced by their N-substituent; Z-isomer of BPI itself without N-substituent is a thermally stable form, while E-isomer with a Z-stilbene skeleton is more thermally stable for N-substituted BPIs as a result of steric distortion due to repulsive interaction between the N-substituent and the benzylidene phenyl ring. UV irradiation of low-molecular N-substituted BPIs and polymethacrylates with E-BPI side chains in solution results exclusively in the E/Z photoisomerization without any side reaction including photodimerization, Photoirradiation of thin films of BPI polymers leads to photoisomerization at the early stage, followed by the gradual decrease of absorption bands ascribable to BPI moieties as a result of [2+2] photodimerization, leading to insolubilization. Quantum efficiencies for the photocrosslinking are much smaller, displaying that the photoisomerization is a predominant reaction even in solid films. Dichroism of the chromophores is induced by linearly polarized light irradiation of thin films of BPI polymers due to the photoisomerizability of BPI units. Further discussion is made on factors affecting the photochemical behavior of BPI polymers.