Phototuning

The photoregulation of the catalytic adivity of 28-Ba2 in the ethanolysis of 29 is illustrated by an experiment (Figure 5.9) in which the catalyst is phototuned HIGH / LOW several times during the reaction by virtue of the complete interconvertibility of stationary states. 

Fig. 13.17 Isomerization of phototunable AChR ligand 15 and structure of Congo Red 16.

Azobenzene systems represent very attractive phototriggers in Ch LCs, thanks to their resistance to photofatigue, the simplicity of the molecules, and the ease of modification of their molecular structures. This chapter first describes helical twisting ability of chiral azobenzene compounds by focusing the structural effects on HTP as well as photochemical change in HTP, and then phototuning of helical structures of Ch LCs through the trans-cis photoisomerization of the chiral azobenzene compounds for applications to optical devices. 

This section discusses the photochemical switching of selective reflection, transparency, helical sense, and lasing through the phototuning of helical structure of the Ch LCs by photoisomerization of chiral azobenzene compounds. 

Tamaoki et al. reported a series of planar chiral dopant which was employed in commercially available nematic LC to achieve phototunable reflection colors [69, 70]. These compounds were designed based on an azobenzenophane compound having conformational restriction on the free rotation of naphthalene moiety to impose an element of planar chirality. Due to the good solubility, moderately high HTPs, and large changes in HTPs during photoisomerization of the dopant, a fast photon mode reversible color control in induced CLCs was achieved. 

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