Photoinduced Reorientation and Photofunctional Control of Liquid Crystalline Copolymers with in Situ-Formed N-Benzylideneaniline Derivative Side Groups

Birefringence and Orientation Direction Control of Photoalignable Liquid Crystalline Copolymer Films Based on In Situ Modification of Mesogenic Groups

Controlling the birefringence of optical films is imperative to fabricate thin birefringent optical devices. Here, new photoalignable liquid crystalline copolymers (PLCPs) with 4-formylphneyl benzoate (PA) and cinnamic acid (CA) side groups are synthesized, which attain high photoreactivity and controllability of the orientation direction. Additionally, the exposed films are treated with 2-aminofluorene (AF) for an in situ condensation of PA with AF to form a Schiff base with a high inherent birefringence. Birefringence of the photoaligned film can be controlled up to 0.45 without disturbing the photoinduced orientation structure.

Photo-Durable Molecularly Oriented Liquid Crystalline Copolymer Film based on Photoalignment of N-benzylideneaniline

Copolymer films of photoalignable liquid crystalline (LC) copolymethacrylates comprised of a phenyl benzoate mesogen connected with N-benzylideneaniline end moiety (NBA2) and benzoic acid (BA) side groups exhibit a photoinduced reorientation behavior. Significant thermally stimulated molecular reorientation attains a dichroism (D) greater than 0.7 for all copolymer films and a birefringence of 0.113–0.181. In situ thermal hydrolysis of the oriented NBA2 groups decreases the birefringence to 0.111–0.128. However, the oriented structures of the film are maintained, demonstrating a photo-durability, even though the NBA2 side groups photo-react. The hydrolyzed oriented films show higher photo-durability without changing their optical properties.

Photoinduced Reorientation and Polarized Fluorescence of a Photoalignable Liquid Crystalline Polymer

Thermally stimulated photoinduced reorientation of liquid crystalline (LC) polymethacrylate composed of a phenyl benzoate mesogen connected with N-benzylideneaniline (NBA2) end moiety exhibits a significant molecular reorientation (D > 0.7) when the film is exposed to linearly polarized 313 nm light and subsequently annealed in the LC temperature range of the material. Hydrolysis of the NBA2 end moieties yields an oriented mesogen with phenylamine moieties without distorting the oriented structure. In situ condensation of 2-hydroxybenzaldehyde derivatives and phenylamine moieties yields oriented N-salicylideneaniline side groups. The resultant film displays a polarized fluorescence with a polarization ratio up to 3.4.

Polarized Fluorescence of N-Salicylideneaniline Derivatives Formed by In Situ Exchange from N-Benzylideneaniline Side Groups in Photoaligned Liquid Crystalline Copolymer Films

Polarized fluorescence of oriented N-salicylideneaniline (SA) derivatives is explored based on the thermally stimulated photoinduced molecular reorientation of liquid crystalline (LC) copolymethacrylate with N-benzylideneaniline derivative (NBA2) and benzoic acid (BA) side groups. The LC copolymer films show significant cooperative molecular reorientation of the NBA2 and BA side groups (D > 0.7). Subsequent thermal hydrolysis of the NBA2 side groups yields free phenylamine moieties. These moieties can form oriented SA derivatives via in situ condensation with 2-hydroxybenzaldehyde derivatives. The excited-state intermolecular proton transfer of the oriented SA molecules induces polarized fluorescence at 510-548 nm with a polarization ratio up to 6.2. Direct in situ exchange from the oriented NBA2 to SA derivatives achieves polarized fluorescence similar to that of the SA side groups.

Fabrication of Polarization Grating on N-Benzylideneaniline Polymer Liquid Crystal and Control of Diffraction Beam

Photoresponsive photoalignable liquid crystalline polymers composed of phenyl benzoate terminated with N-benzylideneaniline were evaluated. These polymers are capable of axis-selective photoreaction, photoinduced orientation, and surface relief grating formation. Polarization holography using an He-Cd laser beam at a wavelength of 325 nm demonstrated the formation of a surface relief grating with a molecularly oriented structure based on periodic light-induced reorientation and molecular motion. Electrical switching of diffracted light using an electric field response of twisted-nematic cell containing a low-molecular-weight liquid crystal in combination was also demonstrated.