Thermal Isomerization Kinetics of Azophenols in Liquid-Crystalline and Glassy Media

Thermal Isomerization Kinetics of Azophenols In Liquid-Crystalline and Glassy Media 

As it has been already mentioned, the potential applicability of azobenzene-based materials is mainly determined by the thermal isomerization rate of the photoactive azo dye used, which, in turn, is related to its molecular architecture. In LC-based materials, however, the azo dye must operate within an ordered host matrix. In this medium, both the chemical nature and the intrinsic order of the LC matrix might influence the rate of the isomerization step and, thereby, the properties of the final material. Remarkably, this point is especially critical for azophenolic dyes since their thermal isomerization rate depends dramatically on the local environment where they are embedded. However, after a careful design, azophenol-based liquid-crystalline and glassy materials can exhibit thermal isomerization rates as fast as those of the monomers in solution, even without the presence of any solvent [41]. Thus, it will be the main aim of the present subsection to provide the reader the main clues for this purpose to be achieved. 

260 I 11 Tautomerizable Azophenol Dyes Cornerstones for Advanced Light-Responsive Materials 

As it has been anticipated above, the subtle manipulation of intermolecular interactions allows to transfer the very fast isomerization kinetics exhibited by azophenols in certain organic solvents to solvent-free liquid-crystalline and glassy thin-film materials (and even to solid materials, see Section 11.5). As a whole, the covalent attachment of inversion-isomerizing azo dyes, like 6, to a main polysiloxane backbone as a side-chain group does not overly influence 

To summarize, achieving control over intermolecular interactions occurring either between the azophenol moieties and their environment or between themselves enables to transfer the fast thermal isomerization rate exhibited by hydroxy-substituted azo dyes in ethanol and acetonitrile solutions to both nematic and glassy thin films. Such a feature permits the generation of fast responding solvent-free photoactive systems with great potential applicability within materials science and actual technology. 

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