Self-Assembled Switching Gels with Multiresponsivity
and Chirality
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Abstract
A multiresponsive
hydrogel material consisting of a commercial
cationic surfactant and an azobenzene derivative functionalized with
four carboxylic acid groups was constructed. The achiral azobenzene
molecule as a gelator produces chirality at the supramolecular level
in the presence of H<sup>+</sup>. The acid-induced gelation and morphology
change of supramolecular gels were investigated in detail by cryogenic
transmission electron microscopy (cryo-TEM), rheological measurements,
circular dichroism (CD), and <sup>1</sup>H NMR spectra. Based on the
results, a mechanism of the intermolecular H-bond-directed gelation
and supramolecular chirality was proposed. Other than the pH sensitivity,
the microstructure and the chirality of the hydrogel demonstrate reversible
switching behavior in response to photoirradiation, on account of
the photoisomerization of the azobenzene derivative. Accordingly,
a chiroptical switch comprising four different states in response
to pH and light stimuli is strategically constructed. Not only does
the present system provide a good opportunity for investigating the
gelation-induced supramolecular chirality by symmetry breaking totally
based on achiral molecules, but it also proposes a new strategy to
build multiresponsive supramolecular switches as particularly attractive
for the future development of functional materials