Photoinduced Chirality in an Azobenzene Amorphous Copolymer Bearing Large Birefringent Moiety

A photoresponsive amorphous copolymer that consists of cyanoazobenzene and a large birefringent moiety with extended π-conjugation was recently designed and synthesized. It has been confirmed that this copolymer exhibits a very large optical rotation of 41°/µm under the optimized excitation conditions practically determined within our optical setup, i.e., 457.9 nm, 30 mW and ellipticity=-0.5. The large rotation angle observed could be attributed to the increment of the order parameter of the polymer side chains promoted by the introduction of the extended π-conjugated moiety. Even more, the dependence of optical rotation on beam power, wavelength and ellipticity of the excitation beam has been examined. The phenomenon of photoinduced chirality in an azobenzene amorphous copolymer is discussed and analyzed on the basis of general ellipsometry by solving the transformation matrix of the sample.