Optically active polymethacrylates with side-chain L-lactic acid residues connected to push-pull azobenzene chromophores

Novel optically active methacrylic homopolymers with side-chain L-lactic acid moieties interposed through eater bonds between the main chain and trans-4-azobenzene chromophores bearing in the 4'-position electron withdrawing groups, such as the cyano and nitro residues, have been synthesized and structurally characterized. Investigation by circular dichroism of the chiroptical and conformational properties of the polymers in solution indicates a much higher optical activity of these latter with respect to that of the corresponding low molecular weight model compounds, purposely prepared, due to the presence of dissymmetric conformations of one prevailing handedness. The trans to cis photoisomerization kinetics of the azoaromatic double bond has been measured in solution for polymers and models and the resulting data compared with those of previously reported similar photochromic derivatives. The influence of the nature of the electron withdrawing group in the 4'-position of the azobenzene chromophore on the chiroptical properties of the polymers is also discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.