Synthesis of polycatenar-type organogelators based on chalcone and study of their supramolecular architectures

We synthesized a series of compounds belonging to a new class of polycatenar-type organogelators, comprising a cyanochalcone unit and a half disklike phenyl group with two or three long alkoxy chains, and investigated their supramolecular assembly with respect to their molecular structures. They formed very stable organogels in n-alkanes, cyclohexane, and alcohols. In the absence of a cyano group, the compound did not show any gelation ability. Dry gels were prepared by freeze-drying the organogels from hexane, and their structures were investigated by SEM and XRD. The SEM images of the dry gels showed the presence of elongated fibers, which formed a gel network. The dry gels exhibited different packing arrangements, depending on the volume fraction of the flexible tails in the gelator. The gelators were assembled into a head-to-tail type dimer by a dipole-dipole interaction between the polar head groups and further organized into columnar or layer structures through a pi-pi interaction. The gelators with three alkoxy tails formed hexagonal, square, and rectangular columnar structures, depending on the tail length, while the gelator with two alkoxy tails formed a layer structure. The organogels were photoresponsive. Upon photoirradiation, the [2 + 2] addition reaction of the chalcone units occurred, which induced a gel-to-sol transition.