Photo-responsive cholesterol-substituted diacetylenic organogels: Morphology tuning, photo-switching and photo-polymerization

A novel cholesterol derivative organogelator (CAZODA) containing both azobenzene and diacetylenic units is synthesized. By using XRD, CD, TEM and SEM characterization, the gelation behavior, microscopic morphology and molecular packing structure in CAZODA assemblies are investigated in detail. It is found that the concentration of the CAZODA at the initial stage plays a crucial role in tuning the microstructure from helical fibers to spherulitic gel networks. Upon UV irradiation at 365 nm, the photo-induced transition of the helical packing structures for CAZODA assemblies has been demonstrated by CD characterization, and an explanation based on the co-assembly of both trans- and cis-form CAZODA has been proposed. In addition, upon irradiation at 254 nm for 3 h, the above organogel can be polymerized with concomitant color change from yellow to red. The polymerized gel exhibits enhanced stability upon thermo or photo-stimuli.