Photochemical Control of Lasing

Recently, Ch LCs have attracted interest as tunable photonic band gap materials (Ozaki, 2007), because the Ch LCs possess photonic band gap properties as well as response to the external stimuli (John, 1987 Yablonovitch, 1987). 

A Ch mixture of E44/S81 l/m-azo-9/DCM (73.1/22.2/4.3/0.4 in wt%) was prepared (Fig. 10.27). DCM is a laser dye. This mixture showed a Ch phase above room temperature up to 62°C Ch 62°C I. m-azo-9 and S811 gave left-handed and right-handed helices when they were added in E44. 

The mixture was injected into a homogeneous glass cell with 25-pm cell gap to obtain a planar molecular orientation. The longer edge of the reflection band of the Ch LC was adjusted to the emission maximum of DCM as shown in Fig. 10.28 

By excitation with the second harmonic light of Nd-YAG laser at lower light intensity, a sharp band at 532 nm as well as a broad band at 565nm were 

Azobenzenes have simple chemical structures and exhibit simple photoisomerization between the trans- and cis form. However, they can really provide various photofunctions by their combination with sophisticated systems such as Ch LCs. The Ch LCs have a good potential for display applications, because they show interesting optical properties depending on the helical structures and the textures. Many types of optical materials can be created by the use of the photoisomerization of chiral azobenzenes in the Ch LCs. New ideas, including design of molecules and systems, may allow us for future materials not only in the field of optics but also in other fields. 

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