Synthesis and Characterization of Segmented Liquid Crystalline Polymers with the Azo Group in the Main Chain

The synthesis of 4'-hydroxyphenyl(4-hydroxy-3-allyl)azobenzene is reported. The molecule is mesogenic and it can be used for preparing nematic main-chain segmented polymers. The nematic phase is the result of the effect of the side allyl group which, while it destabilizes the crystalline phase, does not affect the occurring of the nematic order. In the crystalline state, a large hexagonal unit cell containing five to six chains is observed for polymers with longer flexible spacer in the chain. Chloroform solutions and thin films of polymers absorb in the UV-visible range, at approximately 332 and 439 nm, corresponding to the p - p* and n - p* electronic transitions of azoaromatic chromophores, respectively. Under appropriate UV irradiation we have obtained the photoisomerizations trans-cis and cis-trans, which are fully reversible in the case of solutions. In the solid state a photostationary state is reached