Photoinduced motions in azo-containing polymers.

Photoalignment of Liquid-Crystal Systems.

Coumarins in polymers: From light harvesting to photo-cross-linkable tissue scaffolds

Light-driven phenomena both in living systems and nonliving materials have enabled truly fascinating and incredible dynamic architectures with terrific forms and functions. Recently, liquid crystalline materials endowed with photoresponsive capability have emerged as enticing systems. In this Review, we focus on the developments of light-driven liquid crystalline materials containing photochromic components over the past decade. Design and synthesis of photochromic liquid crystals (LCs), photoinduced phase transitions in LC, and photoalignment and photoorientation of LCs have been covered. Photomodulation of pitch, polarization, lattice constant and handedness inversion of chiral LCs is discussed. Light-driven phenomena and properties of liquid crystalline polymers, elastomers, and networks have also been analyzed. The applications of photoinduced phase transitions, photoalignment, photomodulation of chiral LCs, and photomobile polymers have been highlighted wherever appropriate. The combination of photoc...

Light-Driven Liquid Crystalline Materials: From Photo-Induced Phase Transitions and Property Modulations to Applications.

The review describes the status of the studies and the recent achievements in the field of photoalignment of liquid crystals. An update classification of photoaligning materials and exposure schemes, and analyzes of the relationship between the molecular structure of the materials and characteristics of LC alignment are provided. In addition, bulk mediated photoalignment and combination of photoalignment with other alignment methods are discussed. Along with traditional, recently proposed applications of the photoalignment technique are considered.

Photoalignment of liquid crystals: basics and current trends

Photoproduct distribution in films of cinnamate polymers was analyzed to reveal the contribution of both photoisomerization and photodimerization to LC alignment photoregulation. A polymethacrylate with o-cinnamate side chains displayed preferential formation of Z-isomer while the dimerization takes place more favorably for other polymers including poly(vinyl cinnamate). On the basis of the relationship between photoproduct distribution and liquid crystal photoalignment and on the reversibility of the photoinduced reorientation of a liquid crystal, it was concluded that the photoalignment results from the polarization photoisomerization of cinnamate residues in the same manner as that of photochromic moieties like azobenzenes, whereas the (2 + 2) photodimerization plays a role in enhancing the thermal stability of the homogeneous photoalignment.

Photoreactivity of Polymers with Regioisomeric Cinnamate Side Chains and Their Ability To Regulate Liquid Crystal Alignment

The mechanism of azimuthal reorientation of nematic liquid crystals induced by linearly polarized light irradiation of thin films of polymers with cinnamate side chains has been discussed. It has been concluded that the photoalignment is induced not by the polarized photodimerization, but by polarized photoisomerization, based on the following results. First, spectral analysis of olefinic chromophores upon UV irradiation has shown that a predominant photochemistry in films is the E/Z photoisomerization which results in the dichroism of the chromophores. Second, the alignment direction can be altered by subsequent irradiation with polarized light with a different electric vector. Photodimerization plays a role in enhancing the thermal stability of photoalignment.

Role of E/Z Photoisomerization of Cinnamate Side Chains Attached to Polymer Backbones in the Alignment Photoregulation of Nematic Liquid Crystals*1

Command surfaces 13(1): photoregulation of in-plane alignment of nematic liquid crystals by cinnamate pendant polymer films.

Photo-and thermal isomerization of poly[2-(2-methacryloyoxy)azobenzene] derivatives was investigated both in solution and in film state. In the photo-induced trans-cis isomerization, the rate in film slate was smaller than that in solution. The kinetics of the thermal back reaction was proved to depend on the copplymerization ratio of the polymer. Linearly polarized light (LPL) irradiation of a thin film of the polymer induced dichroism of the film. The degree of the dichroism was related to the Tg of the polymers. In-plane alignment of nematic liquid crystals (LCs) was regulated by photodichroic thin films. Heat treatment of a film before irradiation was a important factor for the photoregulation.

Photochromic Behavior of Thin Films of Polymehacrylate Substituted with Laterally Attached Azobenzenes Displaying Liquid Crystal Alignment Photocontrol

Photoproduct distribution in films of cinnamate polymers was analyzed to reveal the contribution of both photoisomerization and photodimerization to LC alignment photoregulation. A polymethacrylate with o-cinnamate side chain displayed preferential formation of Z-isomer while the dimerization takes place more favorably for others including poly(vinyl cinnamate). Based on the relationship between photoproduct distribution and liquid crystal hotoalignment and on the reversibility of the photoinduced reorientation of a liquid crystal, it was concluded that the photoalignment results from the polarization photoisomerization of cinnamate residues in the same manner as that of photochromic moieties like azobenzenes whereas the (2+2) photodimerization plays a role in enhancing the thermal stability of the homogeneous photoalignment.

Yasuhiro Akita

Papers

Photoreactivity of Polymers with Regioisomeric Cinnamate Side Chains and Their Ability To Regulate Liquid Crystal Alignment

Role of E/Z Photoisomerization of Cinnamate Side Chains Attached to Polymer Backbones in the Alignment Photoregulation of Nematic Liquid Crystals*1

Command surfaces 13(1): photoregulation of in-plane alignment of nematic liquid crystals by cinnamate pendant polymer films.

Photochromic Behavior of Thin Films of Polymehacrylate Substituted with Laterally Attached Azobenzenes Displaying Liquid Crystal Alignment Photocontrol

Relationship between photoreactivity and ability to regulate liquid crystal alignment of polymers with cinnamate side chains