Solvation effects with a photoresponsive two-component 12-hydroxystearic acid-azobenzene additive organogel

A light-triggerable azobenzene amine derivative (additive 1) was synthesized and then introduced into organogels of 12-hydroxystearic acid (HSA) in the molar ratio of 1:3. The organogels (HSA/1) consisting of additive 1 and HSA were analyzed by H-1 nuclear magnetic resonance (NMR), Fourier transform-infrared (FT-IR), and X-ray diffraction (XRD). The homogeneity of the gel networks was observed using field emission scanning electron microscopy (FE-SEM). Additive 1 formed a complex with HSA in HSA organogels due to salification between the terminal amine group of additive 1 and the carboxylic acid group of HSA. Additive 1 in the gels of HSA/1 showed the potential for photo-isomerization, and we achieved a reversible control of HSA/1 sol-gel transition in toluene by the alternating irradiation with UV and visible light. Interestingly, the opposite phenomenon was observed in CHCl3 system, namely, the orange solution of HSA/1 in CHCl3 was turned to a red-transparent gel by exposure to UV light. (C) 2012 Elsevier Inc. All rights reserved.