Synthesis and characterization of novel photochromic liquid crystalline and amorphous polymers for optical storage

Optically induced orientation of azochromophores and photoinduced surface relief gratings (SRG) formation have been investigated in thin films of amorphous and liquid crystalline azo polymers.; Poly {lcub}2-{lcub}4-[[N-(2 methacryloyl) ethyl]-N-ethy]phenylazo{rcub}-6 nitro-benzothiazole) or (PBTAMC) was prepared and its optical storage properties were investigated. Comparison is made with other push-pull azobenzene-containing polymers in order to determine the effect of the strength of electron acceptor group on photoisomerization and photoinduced orientation. Transient absorption spectroscopy was employed to determine the rate constant of thermal cis-trans isomerization (k) and cis-lifetime of azochromophores. When the azochromophore has only one electron withdrawing group, both k and the rate constant of inducing birefringence increase with increasing the strength of electron acceptor group. Introducing an additional electron acceptor group, as in PBTAMC, decreases the level of birefringence and the rate of photoorientation. This behavior is correlated with the instability of azo dipoles which undergo photobleaching.; Three new series of push-pull bisazobenzene-containing copolymers, namely PM2EY, PM2MY and PM4MY were synthesized and cast as thin films to study their photoinduced molecular orientation. These copolymers vary through the content of bisazo dye, the spacer length between the backbone and chromophore, the backbone flexibility and the substituent type at electron-donor group. All these structural factors influence the polymer response to irradiation with linearly polarized light. Differential scanning calorimetry (DSC), polarized optical microscopy (POM) and X-ray diffraction measurements were employed to analyze and identify the mesophases exhibited by some members of these series. Bisazo-based polymers show an enhancement in both optically induced birefringence and stability in comparison with monoazo-containing polymers. Information about the orientational distribution of the chromophores and their changes upon irradiation and thermal treatment were obtained from polarized UV-Vis spectroscopy.; Surface relief gratings were inscribed in films of copolymers of methyl methacrylate with a methacrylate containing a bisazochromophore (PM2EY-MMA ). The efficiency of grating fabrication depends on the copolymer composition and on the polarization of the laser beam. Besides simple gratings with a sinusoidal shape, as revealed by atomic force microscopy, more complex gratings with “beat” or “egg-crate” like structures could be inscribed sequentially on the same spot. Such gratings are stable at room temperature but can be erased by thermal treatment. The phase relationship between the light intensity pattern and the surface profile was determined by analyzing the surface deformation induced by 1D Gaussian laser beam.