Binary Supramolecular Gel of Achiral Azobenzene with a Chaperone Gelator: Chirality Transfer, Tuned Morphology, and Chiroptical Property

Abstract

Binary supramolecular gels based on achiral azobenzene derivatives and a chiral chaperone gelator, long-alkyl-chain-substituted L-Histidine (abbreviated as LHC18) that could assist many nongelling acids in forming gels, were investigated in order to fabricate the chiroptical gel materials in a simple way. It was found that although the carboxylic acid-terminated achiral azobenzene derivatives could not form gels in any solvents, when mixed with LHC18 they formed the co-gels and self-assembled into various morphologies ranging from nanotubes and loose nanotubes to nanosheets, depending on the substituent groups on the azobenzene moiety. The ether linkage and the number of carboxylic acid groups attached to the azobenzene moiety played important roles. Upon gel formation, the localized molecular chirality in LHC18 could be transferred to the azobenzene moiety. Combined with the trans-cis isomerization of the azobenzene, optically and chiroptically reversible gels were generated. It was found that the gel based on azobenzene with two carboxylic acid groups and ether linkages showed clear optical reversibility but less chiroptical reversibility, whereas the gel based on azobenzene with one carboxylic acid and an ether linkage showed both optical and chiroptical reversibility. Thus, new insights into the relationship among the molecular structures of the azobenzene, self-assembled nanostructures in the gel and the optical and chiroptical reversibility were disclosed.

Molecular photoswitches in aqueous environments

“…3,[12][13][14][15] While photocages are photolabile protecting groups that are cleaved upon irradiation and hence, can only be activated once, 13,16,17 photoswitches can be reversibly interconverted between different (functional) isomers. 3,18 This reversible nature makes them interesting candidates for a wide range of applications, including those that take place in water, where they act as photoresponsive amphiphiles, [19][20][21][22][23][24][25][26][27] hydrogel constituents, 28,29 probes for chemical biology, [30][31][32] or bioactive agents in photopharmacology. 6,7,30,33 Molecular photoswitches are typically organic molecules bearing extended aromatic systems to make them responsive to (visible) light.…”

Effect of Alkyl Chain Length of N‐Alkyl‐N′‐(2‐benzylphenyl)ureas on Gelation

“…Another typical strategy in LMWG design is the introduction of long alkyl groups to obtain van der Waals interactions as an association force and to avoid crystallization [23–27] . The question is: Which length of alkyl group is appropriate?…”

Polydiacetylene (PDA) based supramolecular gel upon coassembly with a bolaamphiphilic cogelator

“…Finally the molecular packing of the complex was further evaluated by small angle XRD characterization (Figure S11 in Data S1). Two obvious Bragg diffraction peaks appeared at 2θ values of 5.5° and 9.3° along with a small peak at 13.1°, which is close to the typical (001) fashion pattern, indicating a well‐defined lamellar interpenetration structure as a basic unit for the complex in the gel system 26‐28 …”