Self-Assembled Switching Gels with Multiresponsivityand Chirality.

A multiresponsivehydrogel material consisting of a commercialcationic surfactant and an azobenzene derivative functionalized withfour carboxylic acid groups was constructed. The achiral azobenzenemolecule as a gelator produces chirality at the supramolecular levelin the presence of H+. The acid-induced gelation and morphologychange of supramolecular gels were investigated in detail by cryogenictransmission electron microscopy (cryo-TEM), rheological measurements,circular dichroism (CD), and 1H NMR spectra. Based on theresults, a mechanism of the intermolecular H-bond-directed gelationand supramolecular chirality was proposed. Other than the pH sensitivity,the microstructure and the chirality of the hydrogel demonstrate reversibleswitching behavior in response to photoirradiation, on account ofthe photoisomerization of the azobenzene derivative. Accordingly,a chiroptical switch comprising four different states in responseto pH and light stimuli is strategically constructed. Not only doesthe present system provide a good opportunity for investigating thegelation-induced supramolecular chirality by symmetry breaking totallybased on achiral molecules, but it also proposes a new strategy tobuild multiresponsive supramolecular switches as particularly attractivefor the future development of functional materials. [ABSTRACT FROM AUTHOR]