Supramolecular assembly of dendronized diacetylenes into thermoresponsive chiral fibers and their covalent fixation through topochemical polymerization

Abstract

By combination of dendritic topological structures with photopolymerizable diacetylene, here we report on supramolecular chiral assembly of the dendronized diacetylenes in water. These dendronized diacetylenes are constituted with three-fold dendritic oligoethylene glycols (OEGs), bridged with a dipeptide from phenylalanine and glycine. These dendronized amphiphiles exhibit intensive propensity to aggregate in water and form helical fibers, which show characteristic thermoresponsive behavior with phase transition temperatures dominated by hydrophilicity of the dendritic OEGs. Topochemical polymerization of these supramolecular fibers through UV irradiation transfers them into the covalent helical dendronized polydiacetylenes. Chirality of these dendronized polydiacetylenes can be mediated through the thermally-induced phase transitions, but is also intriguingly dependent on vortex via stirring. Through stirring the solutions, chiralities of the dendronized polydiacetylenes are inverted, which can be reversibly recovered after keeping still the solution. Hydrogels are formed from these dendronized diacetylenes through concentration-enhanced interactions between the supramolecular fibers. Their mechanical properties can be greatly increased through thermally-enhanced interactions between the fibers with storage moduli increased from 20 Pa to a few hundred Pa. In addition, through photo-polymerization, the supramolecular fibers are transferred into covalent dendronized polydiacetylenes, and the corresponding hydrogels show much improved mechanical properties with storage moduli about 10 kPa.