Irradiation with circularly polarized light of a film of an achiral azobenzene liquid crystalline polymer induces chirality. Circularly polarized light with opposite handedness produces enantiomeric structures. A chirooptical switch based on this phenomenon is reported.

Dynamical experimental studies on the diffraction efficiencies and the formation of birefringence grating and surface relief grating on doped and/or covalently bonded azobenzene derivatives containing polymer films were carried out using laser beams with different polarizations. From polarization analyses of the first-order ((1) diffracted beams, the contributions to the diffraction efficiency are separated into an anisotropic (or birefringence) part and a surface relief part. During the growth of the gratings the dynamical responses of both contributions appear to be quite distinct, and estimates of the time variations of the anisotropic phase shift, ∆ , due to the induced birefringence and of the surface relief height, 2∆d, due to the polymer mass transport are obtained. Calculations and simulations of the theoretical expressions allow us to confirm the experimental findings and to reproduce all the observed polarized first-order diffraction curves with good agreement, even when the surface relief is important in the covalently bonded azobenzene polymer films. In these functionalized systems we thus conclude that very efficient permanent surface relief gratings are formed using right-circular and left-circular interfering laser beams.

Optically isotropic films of an amorphous copolymer containing azobenzene moieties (pDR1M-co-MMA) were irradiated by interfering two circularly contrarotating polarized laser beams and permanent holographic diffraction gratings were prepared. These involve the formation of both birefringence and surface relief gratings. Using the Raman confocal microspectrometry, we have recorded various resonance enhanced polarized Raman spectra from the surface profile in order to get new insight into the orientational and angular distributions of the chromophore species. Different theoretical equations of the Raman scattering intensities, including a treatment taking into account the effect of the high numerical aperture objective, were thus derived. Calculations and simulations of these equations allowed us to extract the second 〈P 2 〉 and fourth 〈P 4 〉 coefficients of the chomophore orientation function in various regions of the surface grating and to obtain the corresponding information entropy normalized distribution functions. From the various shapes of the distribution functions we discuss the photoinduced effects and suggest that mass-transport effects must be also effective. Finally, in agreement with the modulated relative Raman intensities and four distinct distribution functions observed along the surface grating, we conclude that the orientational orders are primarily generated by an angular dependent photoselection process, which acts as an initializing force in the establishment of the various molecular organized domains. Such molecular organizations could occur in the viscoelastic state of the polymer and be responsible for an amplification of the light induced anisotropic effects in some regions (at the bottoms) and for a significant perturbation of the orientations in other regions (at the tops of the surface profile). In agreement with previous studies about the mechanisms of grating formation, these results are consistent with a model involving the existence of large pressure gradients due to a viscoelastic flow of the polymer.