Synthesis and mesomorphic properties of photoresponsive azobenzene-containing chromophores with various terminal groups

A series of azobenzene-containing chromophores end-capped with cholesteryl group were synthesized using esterification reactions to investigate the effect of terminal groups and spacer length on mesomorphic properties and photoreactivity of photochromic compounds. The chromophores were composed of liquid crystalline mesophases with six or eleven methylene segments as spacer, and with electron-donating (methoxy) and electron-withdrawing (nitro) terminal groups. The target compounds were characterized by nuclear magnetic resonance spectroscopy, differential scanning calorimeter, polarizing optical microscopy, absorption, and photoluminescence spectroscopies. All the chromophores with long methylene segments revealed cholesteric liquid crystalline phases. We investigated the effect of these photochromic compounds’ structures on E/Z photoisomerization under UV irradiation. Chromophores, incorporating the electron-withdrawing nitro-group, underwent a faster rate of Z to E isomerization in darkness than the electron-donating methoxy groups did; the isomerization process proceeded via a rotation mechanism.

► A series of azobenzene derivatives were designed and synthesized.
► Mesophases were confirmed using DSC and POM analyses.
► We studied the E/Z isomerization using UV–vis spectroscopy.
► The influence of terminal groups and spacer length on photoreactivity and mesomorphic properties.