The dynamics of the photochemical phase transition process of guest/host liquid crystals (LCs) containing an azobenzene derivative as a photosensitive chromophore was studied. We proposed a model for the photochemical phase transition of the guest/host LCs and simulated the change in transmittance through LCs due to the phase transition on the basis of this model. Upon irradiation at 366 nm, the cis isomer was generated randomly in the irradiated site, and then the transmittance of the probe light was slightly decreased because of the disturbance of the alignment of the nematic (N) phase by the cis isomers. Upon further irradiation, the N-to-isotropic (I) phase transition took place in local domains, and the transmittance of the probe light decreased with the growth of these local I domains. In the simulations, three factors were found to affect significantly the dynamics of the photochemical phase transition and the change in transmittance of light:  the number of I domains formed by irradiation, the growth rate of the I domains, and the threshold size of the I domains detected with the probe light.

We have developed a technology for a new full-color reflective electrochromic display (ECD) based on the subtractive color mixing model. This improves display brightness and color reproducibility. Additional advantage is simple production process. An active matrix driving of the full-color reflective ECD has been demonstrated successfully.

The in¯uence of the spacer structure on the photochemical phase transition behaviour was explored for azobenzene polymer liquid crystals (azo-PLCs) possessing siloxane spacers in the polymer side chain, and for analogue without the siloxane spacer. The photochemical phase transition of the azo-PLC with the siloxane spacer was found to proceed less e ectively than that of the azo-PLC without the siloxane spacer. It was also con® rmed that the spacer structure does not a ect the trans± cis photoisomerizatio n behaviour of the azobenzene moieties. These results were interpreted in terms of stabilization of the alignment of the mesogens in the liquid crystalline phase by the siloxane spacer, since the siloxane chain is one of the most¯exible spacers and decouples the motion of the polymer backbone from that of the aligned mesogens. Furthermore, the response of the azo-PLCs in the photochemical phase transition was evaluated by means of a laser pulse. The phase transition occurred iñ 300 ms for both samples.

Abstract— A photon‐mode full‐color rewritable image has been demonstrated. Three types of photochromic fulgides having yellow, magenta, and cyan color were used as rewritable dyes. Photochromic fulgides were mixed and coated on a white polyethylene terephthalate film. Upon irradiation with three (red, green, and blue) visible light beams, a wide hue extent, a high white reflectance of over 80%, and a high contrast ratio of over 45:1 were attained. A full‐color image retains its colors for over 1 hour under standard‐office‐brightness conditions (700 lx). The photochemical coloration‐decoloration cycles could be repeated over 100 times without substantial losses.

Photochemical phase transition behavior of polymer azobenzene liquid crystals (LCs) was explored by transmission-mode analysis and reflection-mode analysis. Four samples with different structures were used, which show LC behavior in the trans form but no LC phase in the cis isomer. Attention was focused on the effect of the position of the mesogenic azobenzene moiety in the flexible side chain on the photochemical phase transition behavior. Photoirradiation of a thin film of the azobenzene LCs (-200 nm) in the trans form resulted in the disappearance of the LC phase due to truns-cis photoisomerization of each mesogen. and the LC phase recovered quickly when the irradiated sample was kept in the dark because of thermal cis-trans back-isomerization. In all polymers, the photochemical LC to isotropic ( I ) phase transition was induced in 100-200 ps on laser pulse irradiation. In the sample with an azobenzene located apart from the main chain of the polymer by a spacer, the LC-I phase transition took place almost completely. In the sample with the azobe,nzene moiety in the vicinity of the main chain, however, the photochemical phase transition was induced only locally. These phenomena are interpreted in terms of the mobility of the azobenzene moiety in the side chain and the stability of the LC phase.