Synthesis, layer-by-layer self-assembly and optically induced birefringence of a novel branched side-chain azo polyelectrolyte

A novel polyelectrolyte (PBANT-AC) functionalized with branched electron donating-accepting azobenzene chromophores has been synthesized through post-polymerization azo coupling reaction and characterized by H-1-NMR, FTIR and UV-Vis spectrometry. The degree of functionalization (DF) of PBANT-AC was 17% measured by elemental analysis. The degree of polymerization and its distribution were determined by GPC to be X-n = 588 with a polydispersion index 1.3. A glass transition temperature of 139degreesC was observed from DSC thermogram. H-Aggregation of azo chromophores of PBANT-AC in H2O-THF mixed solvent was detected from UV-Vis spectra and controlled by the ratio of V-THF/V-H2O. The H-aggregates in water-tetrahydrofuran mixture were successfully fabricated into self-assembled multilayers with poly (diallydimethylammonium cloride) by an electrostatic layer-by-layer process. Birefringence and dichroism were optically induced in the self-assembled films under the irradiation of a polarized Ar+ laser beam at 488 nm. The resulting dichroism was easily detected from UV-Vis spectra and exhibited long-term stability. The orientational order parameter obtained was 0.05 for the film. Upon irradiation, the H-aggregates of azo chromophores were changed to 'isolated' form after the cis-trans isomerization.