Synthesis and characterization of photoactive azobenzene-based chromophores containing a bulky cholesteryl moiety

This study describes the synthesis of a series of azobenzene-based chromophores bearing pendent bulky cholesteryl groups, using esterification reactions. The chromophores were composed of liquid crystalline mesophases with six or eleven methylene segments as spacers, and with electron-donating (OCH3) and electron-withdrawing (NO2) terminal groups. The target compounds were characterized by nuclear magnetic resonance spectroscopy, differential scanning calorimetry, polarizing optical microscopy, absorption, and photoluminescence spectroscopies. All the azobenzene derivatives with six or eleven methylene segments revealed chiral nematic phases. We investigated the effects of these photochromic compounds’ structures on E/Z photoisomerization under UV irradiation. Chromophores containing the electron-withdrawing nitro-group (NO2) underwent a faster rate of Z to E isomerization in darkness than the electron-donating (OCH3) groups did; the isomerization process proceeded via a rotation mechanism. Self-assembled aggregates of C6 solution exhibited enhanced fluorescence in THF/water mixtures at 10% water fraction.