Synthesis, chiroptical properties and photoinduced birefringence of optically active methacrylic copolymers bearing side-chain bisazoaromatic moieties

Abstract

Three series of optically active photochromic copolymers, deriving from methyl methacrylate ( MMA) and the chiral bisazoaromatic monomers ( S)-3-methacryloyloxy-1-[4′-phenylazo-(4-azobenzene)]-pyrrolidine [( S)- MPAAP], ( S)-3-methacryloyloxy-1-[4′-cyanophenylazo-(4-azobenzene)]-pyrrolidine [( S)- MPAAP- C] and ( S)-3-methacryloyloxy-1-[4′-nitrophenylazo-(4-azobenzene)]-pyrrolidine [( S)- MPAAP- N], have been prepared and characterized in solution and in the solid state with the aim to evaluate the effect on their chiroptical and thermal properties originated by the insertion of inactive MMA groups along the main chain. The optical activity displayed by the bisazo polymers is discussed in terms of extent of chiral conformation assumed by the macromolecules as a consequence of dipole–dipole interactions between the bisazoaromatic chromophores. The photoinduction of birefringence has been assessed on thin films of the investigated copolymers in order to evaluate their behaviour as materials for optical data storage. The results are interpreted in terms of copolymer composition and conformational stiffness of the bisazoaromatic chromophoric co-units, which are responsible for the optical response rates, and are compared to those of the similar derivatives containing only one azo bond. The observed enhanced thermal properties and the temporal stability appear of interest for a potential use of these materials in nano technologies for all-optical data manipulation and in optoelectronics.