Teppei Yoshioka

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 tuning of the helical structure of cholesteric liquid crystals by photoisomerization of chiral azobenzenes, and their structural effects

Several chiral azobenzene compounds having different chiral substituents were synthesized. A cholesteric phase was induced by mixing each chiral azobenzene compound with a host non-chiral nematic liquid crystal (E44). The helical twisting power (HTP) as well as the change in HTP by trans-cis photoisomerization of the chiral azobenzene compound was dependent on the structure of the chiral substituents. A compensated nematic phase was induced by combination of E44, a chiral azobenzene compound and a non-photochromic chiral compound. Reversible switching between the compensated nematic phase and cholesteric phase was brought about by trans-cis photoisomerization of the chiral azobenzene compound in the liquid crystalline systems. An azobenzene compound substituted with a menthyl group showed the highest efficiency as the trigger for the switching; this efficiency was related to the compactness of the chiral group substituted within the azobenzene core moiety.

Synthesis of chiral azobenzene-based compounds for use in the photochemical tuning of the helical structure of liquid crystals

We have synthesized azobenzene-based molecules containing either one or two chiral groups. A cholesteric phase can be induced by adding the chiral azobenzene compounds to a host nematic liquid crystal. We investigated the effects of the trans-cis photoisomerization of the chiral azobenzene compounds on the properties of the cholesteric phase, such as the helical pitch length. This can be increased or decreased by the photoisomerization of the chiral azobenzene compounds. We discuss the photochemically driven change in the helical pitch of the cholesteric phase with respect to structural effects involving the chiral groups.

The influence of molecular structure on helical twisting power of chiral azobenzene compounds

Photochromic chiral azobenzene compounds with different molecular structures were synthesized, and a cholesteric phase was induced by mixing each chiral azobenzene compound with a non‐photochromic chiral compound in a host nematic liquid crystal, E44. Helical pitch and, thus, helical twisting powers (HTP) of the chiral azobenzene compounds and the non‐photochromic chiral compound were determined by Canos wedge method. Molecular structures of the chiral azobenzene compounds were predicted by means of determining their molecular aspect ratio (L/D) with semiempirical molecular calculations (MOPAC at PM3 level). The effects of molecular structure on HTP of the chiral azobenzene compounds are studied in detail. Molecular structures of chiral azobenzene compounds significantly influence their HTPs.

Discontinuous change in the helical pitch of cholesteric liquid crystals by photoisomerization of a chiral azobenzene molecule

This paper describes the discontinuous change in the helical pitch of a cholesteric liquid crystal (ChLC) by means of the photoisomerization of chiral azobenzene molecules under homogenous alignment conditions. A mixture of E44, R811 and Azo was prepared in the ratio 68/28/4, respectively. R811 and Azo have opposite twisting abilities such that they induce right- and left-handed helices, respectively when added to E44. The mixture was injected into a glass cell having a 2 or 5 µm cell gap, and treated for homogeneous molecular orientation. The wavelength of selective reflection from the ChLC was shifted to shorter wavelengths by the trans-cis photoisomerization of Azo. The change in the helical pitch was not only discontinuous, but also dependent on the cell thickness. The discontinuous change in the helical pitch was estimated to be almost the same as the half turn of the helical pitch in each cell gap, and was dependent on the number of helical half pitches in the glass cell. The homogeneous alignment condition affects the photochemical change in the helical structure of the ChLC system.

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.