Control of Thermally Enhanced Photoinduced Reorientation of Polymethacrylate Films with 4-Methoxyazobenzene Side Groups by Irradiating with 365 and 633 nm Light and Annealing

Abstract

This paper describes two different techniques for thermally enhanced photoinduced reorientation of liquid crystalline polymethacrylate (PLC) films that contain 4-methoxyazobenzene side groups with various alkylene spacer lengths. One is the classical method based on photoselection and rotational diffusion in the steady state of the E/Z photoisomerization, which includes irradiating with linearly polarized (LP) 365 nm light and subsequently annealing in the liquid crystalline (LC) temperature range of the film. The spacer length and exposure dose significantly influence the reorientation direction. In-plane reorientation perpendicular to the electric vector (E) of the LP 365 nm light was generated for PLCs with short spacers, but out-of-plane reorientation with a small degree of in-plane reorientation was predominant for PLCs with long spacers. The other is an alternative technique based on an axisselective Z-to-E photoisomerization using LP 633 nm light and thermally enhanced molecular reorientation. Regardless of the spacer length, a high order of in-plane reorientation parallel to E of LP 633 nm light was accomplished. Polarization UV-vis spectroscopy was used to investigate these reorientational behaviors and to clarify the mechanism.

Photoinduced Chiral Nematic Organization in an Achiral Glassy Nematic Azopolymer

“…130°C, as previously reported by several groups. [32][33][34] After annealing the sample in the nematic phase and quenching at room temperature, X-ray diffraction studies of the homopolymer P100 film confirmed that the nematic phase was frozen in the glassy state. No diffraction peaks were detected in the angle region in which smectic layer difraction can be expected (Fig.…”

“…The H-aggregates and J-aggregates are known to cause a blue shift and a red shift, respectively, of the p-p* band of the azobenzenes and, as a result, broad bands are detected. [34,36] The use of a peak fitting procedure enables the amounts of the chromophores in the different aggregates to be roughly estimated and this allows comparison of the differently treated films. Good and reproducible fitting results were obtained by introducing three peaks with fixed absorption maxima at 334 nm for H-aggregates, 360 nm for non-associated chromophores and 384 nm for J-aggregates according to literature data for similar compounds.…”

Photoswitching properties of photonic crystals infiltrated with polymer liquid crystals having azobenzene side chain groups with different methylene spacers

“…On the other hand, no significant differences of photoisomerization behavior were observed for all polymers in THF after irradiation with UV and visible lights. The peculiar photoisomerization behavior of the PMAz11Ac solid film may be closely related to formation of H-aggregates [19,25] and the out-of-plane molecular orientation of azo-chromophores in the PMAz11Ac, which has longer methylene spacers [22].…”

“…Many studies have described that the photo-orientation behavior of azo-chromophores strongly depends on the mobility of the side chains in azobenzene-containing PLCs [18][19][20][21][22]. Freiberg et al synthesized push-pull type azobenzene-containing polymers with different methylene spacers between the main chain and the azobenzene side group and revealed that the photo-induced birefringence of the azo-choromophores depended on the length of the methylene spacers [23].…”

Photoalignment and Photoinduced Molecular Reorientation of Photosensitive Materials

“…93,94 As shown in Figure 9, the thermally enhanced reorientation of 30 using LP-633-nm light has achieved an in-plane reorientational order greater than 0.8. 95,97 In this case, the orientation behavior is independent of the alkylene spacer length.…”