Synthesis and optical storage properties of a novel polymethacrylate with benzothiazole azo chromophore in the side chain

A new amorphous high-T-g azo polymer with benzothiazole group in the side chain, poly{2-{4-[[N-(2-methacryloyl)ethyl]- N-ethyl] phenylazo}-6-nitro-benzothiazole} (pBTAMC), was prepared and its optical storage properties were investigated in thin films. Comparison is made with three push-pull azobenzene polymers: poly{4-[[2-(methacryloyloxy) ethyl] ethylamino]-4'-(methylsulfonyl) azobenzene}(pDRSAM), poly{4-[2( methacryloyloxy) ethylsulfonyl]- 4'-(diethylamino) azobenzene}(pDRASM} and poly{4-[[ 2-( methacryloyloxy)ethyl] ethylamino]- 4'- nitroazobenzene} (pDR1M) in order to study the effect of chromophore structure on optical storage properties. The thermal cis-trans isomerization behavior of azo groups in polymer films, measured by means of flash photolysis, revealed that the rate constant of thermal isomerization increases with the increase in dipole moment of azo chromophores. In these systems, the relaxation of the cis-isomer was analyzed as the sum of two first-order reactions, a fast and a slow one. The azo chromophore orientation induced by irradiation of polymer films with linearly polarized light was measured as birefringence. Both the level of photoinduced birefringence and the rate of achieving it follow the order pDR1M > pDRASM > pDRSAM > pBTAMC. pBTAMC, which contains the strongest pair of donor-acceptor substituents in the azo chromophore side chain, exhibits the highest stability of the induced order (93% of photoinduced birefringence is maintained after relaxation). In pBTAMC films, the chromophore orientation is accompanied by some irreversible chromophore bleaching.