Masaki Moritsugu

Thermal and Photochemical Control of Molecular Orientation of Azo‐Functionalized Polymer Liquid Crystals and Application for Photo‐Rewritable Paper

A photo-responsive multi-bilayered film consisting of azobenzene polymer liquid crystals (PA6Az1) and poly(vinyl alcohol) (PVA) has been prepared on a glass substrate by alternate spin coating of the polymer solutions. The reflectivity of the multi-bilayered film disappears by annealing at 80 °C. The disappearance of the reflection by the annealing is related to the thermal out-of-plane molecular orientation of PA6Az1 even in the multi-bilayered film, which leads to a very small difference in refractive indices between PA6Az1 and PVA. The reflectance of the multi-bilayered film is increased again by UV irradiation because of the transformation from the out-of-plane orientation to an in-plane random orientation. In this way, on-off switching of the reflection is achieved by combination of the thermally spontaneous out-of-plane molecular orientation and following photoisomerization of PA6Az1 comprising the multi-bilayered film.

Photo-tuning of lasing from a dye-doped cholesteric liquid crystals by photoisomerization of a sugar derivative having plural azobenzene groups

Cholesteric liquid crystal (Ch LC) was prepared by mixing a nematic LC, a sugar derivative having plural azobenzene substituents, and a laser dye. Laser emission from the dye-doped Ch LC was observed at the longer edge of the selective reflection band of the Ch LC. Reversible change in the helical pitch of the Ch LC was caused by the trans-cis photoisomerization of the sugar derivative having plural azobenzene substituents. According to the change in the helical pitch of the Ch LC, the lasing properties were simultaneously affected by the UV and visible light irradiation; laser emission wavelength, intensity, singlemode-multimode.

Photochemical switching behavior of azofunctionalized polymer liquid crystal/SiO2 composite photonic crystal

A photochemically tunable photonic crystal was prepared by infiltrating azopolymer liquid crystal in a SiO2 inverse opal structure. The SiO2 inverse opal film obtained reflected a light corresponding to the periodicity as well as the refractive indices of the inverse opal structure. Linearly polarized light irradiation shifted the reflection band to longer wavelength more than 15nm. This is caused by the formation of anisotropic molecular orientation of the azopolymer. The switched state was stable in the dark, and the reversible switching of the reflection band can be achieved by the linearly and circularly polarized light irradiations.

Photochemical Modulation of the Wavelength of Lasing from a Dye-Doped Cholesteric Liquid Crystal

ABSTRACT This work provides reversible phototuning of the laser emission by means of photoisomerization of chiral azobenzene, causing change in the reversible helical pitch. Cholesteric liquid crystals were prepared by mixing a low molar mass liquid crystal (TKS), a laser dye (DCM), a nonphotochromic chiral compound (S811) and a chiral azobenzene compound (Azo). Lasing from the cholesteric liquid crystal was observed at longer band edge of the selective reflection. Reversible shift of the lasing was brought about by UV light irradiation and following visible light irradiation.

Photon mode color display device by means of isomerization of chiral azobenzene

ABSTRACT Photochromic compounds having plural chiral sites as well as azobenzene groups in a molecule was synthesized by reacting 4-, and 3-, 2-carboxy-4′-hexyloxyazobenzenes with isosorbide, and isomannide. A cholesteric liquid crystal (Ch LC) was induced by adding each chiral azobenzene compound in a nematic LC. Most azo dyes showed photochemical decrease in the helical twisting power ( HTP ) by UV irradiation. The change in HTP was related to the photochemical change in the molecular shape. Reversible control of the reflection wavelength of the Ch LC was achieved over a whole range of visible region by irradiation of UV and visible light.

Photoswitching behavior of sio2 inverse opal films infiltrated with azo-tolane copolymer: Effect of polymer main chain structure

Phototunable photonic band gap materials were prepared by infiltration of a liquid crystalline azopolymer into voids of a SiO2 inverse opal film. Linearly polarized light irradiation resulted in a reversible and stable shift of the reflection band to longer wavelength region due to the transformation of azobenzene groups from random to anisotropic molecular orientation. Acrylate and methacrylate copolymers having both azobenzene and tolane groups in side chain have been synthesized in order to improve switching property. Upon irradiation of linearly polarized light SiO2 inverse opal film infiltrated with methacrylate copolymer showed a larger wavelength shift of the reflection band compared to that of the composite film infiltrated with acrylate copolymer.

Photo-response properties of PBG composite material consisting of inverse opal structure and azo-polymer liquid crystal

Photo-tunable PBG composite material was prepared by infiltration of the polymer liquid crystal (LC) having azo-chromophores in a SiO2 inverse opal structure. The SiO2 inverse opal film infiltrated with the polymer LC reflected a light, which is called Bragg diffraction, corresponding to the periodicity as well as the refractive indices of the inverse opal structure. Linearly polarized light irradiation caused the shift of the the Bragg diffraction band to longer wavelength more than 15 nm. This is caused by the formation of uniaxially anistorpic molecular orientation of the polymer LC. The switched state was stable under interior light, and reversible switching of the reflection band can be achieved by the linearly and circularly polarized light irradiation. This photoswitching property will be suitable for various optical materials such as memory, display so on.

Thermal and Photochemical Properties of Polyethylene Imines Having Azobenzene Side Chain Groups

Polyethylene imines (PEIs) having 4-butylazobenezene group through methylene spacer groups were prepared, and their thermal as well as photochemical properties was investigated. PEI104 having longer methylene spacer was found to form an out-of-plane structure by heating into an isotropic phase and following cooling. The photochemical control of the molecular orientation of PEI104 between in-plane and the out-of-plane structures could be achieved by combination of thermal and photochemical processes.

Synthesis of Photo-Cross Linking Polymer Beads and Application for Micro Fabrication of Periodic Structure

ABSTRACT Photonic crystals having a three dimensional periodic structure have attracted much attention from both fundamental and practical points of view, because of their unique properties in controlling the propagation of light. One of the promising techniques for fabricating three-dimensional (3D) photonic crystal is the preparation of self-assembled colloidal crystal. In this study, we synthesized monodisperse polymer spheres having photo-cross-linking groups which were synthesized by co-polymerization of styrene and vinyl cinnamate. Then we prepared colloid crystal from photo-cross linking beads, investigated about application for microfabrication of colloidal crystal from the change of solubility from cross linking by UV light.

Photochemical on-off switching of structural color of a multi-bilayered film consisting of azobenzene-polymer liquid crystal and polyvinylalcohol

Photo-responsive multi-bilayered film consisting of azobenzene polymer liquid crystals (PAzo) and polyvinylalcohol (PVA) was prepared on a glass substrate by spin coating of the polymer solutions alternately. The reflectivity of the multi-bilayered film disappeared by annealing at 80 °C. The disappearance of the reflection by the annealing was related to the thermal out-of-plane molecular orientation of PAzo even in the multi-bilayered film, leading to a very small difference in refractive indices between PAzo and PVA. The reflectance of the multi-bilayered film was increased again by UV irradiation because of the transformation from the out-of-plane orientation to the in-plane random orientation, resulting in the restoration of difference in the refractive indices. In this way, the on-off switching of the reflection was achieved by combination of the thermally spontaneous out-of-plane molecular orientation and following photoisomerization of PAzo comprising the multi-bilayered film.