Photoinduced anisotropy and LC photoalignment properties of polyvinylcinnamate films

The induction of optical anisotropy caused by linearly polarized light was studied in spin-coated films of poly(vinyl 4-fluorocinnamate), PVCN-F. The photoinduced anisotropy was characterized by UV/Vis and IR dichroism, biref ringence measurements and the alignment of liquid crystals. The generated a nisotropy is discussed with respect to (2+2) photocycloadditions and E/Z ph otoisomerisation. It is shown that both reactions cause anisotropy in the f ilms on irradiation with linearly polarized light. The kinetics of the indu ction of dichroism and birefringence are different caused by the contributi ons of both mechanism. The photoproducts of the photocross-linking does not show a significant dichroism. This is dominated by the photoorientation of the cinnamic ester side groups even in the photocross-linked film. This me chanism also causes the repeated reorientation of the optical axis by chang ing the direction of light polarization in the film plane. Both mechanisms lead to LC alignment caused by the anisotropic interfaces of the films.