Enzymatically synthesized photodynamic polyaniline containing azobenzene groups

A novel polyaniline containing azo groups has been synthesized using horseradish peroxidase catalyzed oxidative free radical coupling of 4,4'-diaminoazobenzene in the presence of hydrogen peroxide. The spectral changes observed indicate polymerization accompanied by trans-cia isomerization, leading to structural constraints in the growing polymer chain. This soluble azo polymer consists of azo groups in the main chain as well as in the side chain. Upon photoexcitation of the polymer in solution, the chromophores undergo structural photoisomerization; The polymer relaxes to a conformation having spectral features identical to those of the conformation prior to photoexcitation if the excitation is carried out within the trans absorption band. Photoexcitation at the cis absorption band or thermal kinetic randomization of the chromophore conformation in the polymer in solution results in relaxation of the structural constraints, which leads to a different constrained conformation.