The Characterization of Photoinduced Chirality in a Liquid-Crystalline Azo Polymer on Irradiation with Circularly Polarized Light

In this study, an achiral liquid-crystalline azo polymer is irradiated with circularly polarized light, and the transmitted polarization data show evidence of photoinduced chirality. When the polarization of the laser is switched from left- to right-handed, the chirality of the polymer film is switched as well. In a more revealing experiment, the handedness of the laser is fixed and the evolution of the ordering is monitored. Two models are described to interpret this result, one based on a uniaxial arrangement with the observed circular anisotropy included on a phenomenological level; the other based on a helical arrangement of chromophores. These models were used to fit the polarization data in order to determine the anisotropic optical constants that characterize the structural arrangement. It was noticed that during the irradiation, the sense of the circular anisotropy switches. This is also discussed in relation to both models presented.