In chiral-liquid-crystal (LC*) phased, LC molecules are aligned helically; hence, the refractive indices of the LC* materials are altered periodically along the helical axis. The LC* materials have unique optical properties, such as selective reflection, that arise from the periodic structure of the refractive index. The wavelength of the selective reflection depends on the helical pitch as it is a Bragg reflection; therefore, we can control the reflective wavelength by controlling the helical pitch. In this study, we observed the mechano-optical behaviors of LC* elastomers, and discussed the relationship between the chemical structures of elastomers and mechano-responsive optical properties. When tensile strain was applied to the films, reversible hypsochromic shift in the reflection wavelength was induced. The results of the mechano-optical behavior observed for the LC* elastomers suggest that LC* materials have potential for application in mechanical sensors for soft robots.
A rod-like Au(I) complex, which has a naphthalene ring in a mesogenic core, was synthesized by complexation of an ethynyl-substituted naphthalene derivative with (tht)AuCl, followed by treatment with 1-pentyl isocyanide. Characterization by NMR and X-ray crystallographic analysis revealed its molecular structure and crystal packing structure. The Au complex was found to exhibit enantiotropic liquid crystallinity. The temperature range in which a liquid–crystalline (LC) phase existed was wider than those for the corresponding LC gold complexes with phenyl or biphenyl moieties reported so far. For the Au complex in this study, photoluminescence was observed at 505 nm in the crystalline phase. In this paper, the relationship between molecular structure and LC behavior or photophysical properties is described by comparing this complex with other rod-like Au complexes.
An azobenzene liquid crystal attached to gold nanoparticles with average diameter of 3.5 ± 1.1 nm was synthesized.
The gold nanoparticles prepared in this study were soluble in common non-polar organic solvents such as toluene, chloroform and so on, but not soluble in polar solvents. The particles exhibited their absorption maximum at around 500 nm due to surface plasmon resonance. We confirmed that the reversible photochemical and thermal isomerization of the azobenzene moieties could also be induced on the surface of the gold nanoparticles by UV irradiation. Furthermore, the azobenzene LCs used in this study showed LC behavior even if they attached to the gold nanoparticles.
Photochemically induced nematic (N)-isotropic (I) phase transition behavior and domain formation of the azobenzene/liquid crystal (LC) mixtures in the presence of non-mesogenic dopants were evaluated. When a bent-shaped non-mesogenic molecule was added to the azobenzene LCs, formation of I domains was formed effectively on photoirradiation to cause the trans-cis isomerization of the azobenzene. The domain formation results from the aggregation of cis isomers, which could be enhanced to more extent with the aid of the bent-shaped dopant with a common structural feature to the cis-azobenzene. When the formation of the I domain proceeds quickly upon photoirradiation, the photochemical phase transition is induced more effectively.
Photoinduced two-dimensional (2-D) and three-dimensional (3-D) alignment behavior of polymer liquid crystals (LCs) with azobenzene moieties was investigated. Two-dimensional alignment of the polymer LCs was brought about on irradiation with linearly polarized light. The effects of various factors on the phenomena were discussed in detail, and experimental conditions and structural parameters of the polymer LCs were optimized. It was found that the response could be enhanced by two methods: chemically tailoring the structure of the polymer LCs and physically modifying the alignment procedure. Three- dimensional alignment of the azobenzene moieties was achieved on irradiation with unpolarized light. It was revealed that the azobenzene moieties were aligned along the propagation direction of the incident light. Photochemically inert mesogens underwent reorientation together with azobenzene moieties in the 2-D as well as 3-D alignment process.
Manipulation of light by light as a stimulus by the use of liquid-crystalline materials was explored, which was aimed at optical switching, optical image storage and optical display. Two types of the liquid-crystalline materials are used: nematic liquid crystals and ferroelectric liquid (FLCs). Several kinds of optical switching and image storage systems were demonstrated by means of photochromic molecules and photosensitive LC alignment layer to induce the change in alignment of the LCs: 1) Fast nematic to isotropic phase transition of azobenzene LCs was induced by the laser pulse in two modes of analysis, transmission mode and reflection mode. 2) Optical switching in FLCs doped with the azobenzene was investigated with regard to photochemical flip of polarization of the FLCs. 3) Optical control of polymer- dispersed LC was explored by means of the azobenzene LC. 4) Optical switching and fabrication of nonrubbed alignment layer based on the novel photophysical principle was achieved in terms of photosensitive polyimide as an LC alignment layer. 5) Optical control of conductivity was performed by the use of LC thiophene derivatives.
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