Synthesis of photoresponsive cholesterol-based azobenzene organogels: dependence on different spacer lengths

Abstract

SummaryA series of azobenzene–cholesterol organogel compounds (M 0 –M 12) with different spacers were designed and synthesized. The molecular structures were confirmed by 1H NMR and 13C NMR spectroscopy. The rapid and reversible photoresponsive properties of the compounds were investigated by UV–vis spectroscopy. Their thermal phase behaviors were studied by DSC. The length of the spacer plays a crucial role in the gelation. Compound M 6 is the only one that can gelate in ethanol, isopropanol and 1-butanol and the reversible gel–sol transitions are also investigated. To obtain visual insight into the microstructure of the gels, the typical structures of the xerogels were studied by SEM. Morphologies of the aggregates change from flower-like, network and rod with different sizes. By using IR and XRD characterization, it is found that intermolecular H-bonding, the solvents and van der Waals interaction are the main contributions to the specific superstructure.

Gel scaffolds and emerging applications in biomedicine

“…5a). 23 The formation of azobenzenecontaining SCJNPs (11) occurred through the intrachain photocrosslinking of linear PPEGMA-b-P(MAAz-co-MAStb) BCP precursors. The SCJNPs showed LC properties, as conrmed via DSC and POM studies.…”

“…5 (a) Reversible photo-controlled release of bovine serum albumin by the azobenzene-containing cellulose nanofibrils-based hydrogel (10). (b) Self-assembly of single-chain Janus nanoparticles from azobenzene (11). (c) Supramolecular self-assembly of an azobenzene-based chiral gel (12).…”

Cholesterol-Based Compounds: Recent Advances in Synthesis and Applications

“…The effect of different spacer lengths containing two, three, five, six, ten, or twelve carbon atoms on cholesterol-based azobenzene organogels 285 and 286 was investigated [76]. For this purpose, a series of seven azobenzene-cholesterol compounds was synthesized through esterification reactions of cholesterol derivatives of 283 (bearing different spacer lengths) with 4′-carboxy-4-methoxyazobenzene 284 carried out in the presence of N , N ′-dicyclohexylcarbodiimide (DCC) and dimethylaminopyridine (DMAP) in dichloromethane, as depicted in Scheme 70.…”

“…Interestingly, among the tested compounds, only 285 ( n = 6) could form a gel, and in specific solvents such as ethanol, isopropanol, and butan-1-ol. Furthermore, the authors concluded that the solvents, intermolecular H-bonding, and van der Waals interactions affected the aggregation mode and morphology of the gels [76].…”

Reversible photoresponsive chiral liquid crystal and multistimuli responsive organogels based on a cholesterol-azobenzene dimesogen

“…[23][24][25] Though the gelation properties of dimesogens were usually not considered, some reports about symmetrical trimesogens incorporating two cholesterol groups as terminal groups at a central azobenzene core unit, were focused on the multiresponsive behaviour combining LC phase formation and gel formation [26][27][28][29] Only recently gelation properties of LC dimesogens combining azobenzene and cholesterol units, have been reported. 30 However, in this case the LC phase characterization was only preliminary and chirality of the formed LC phases was not considered. Herein we report a new unsymmetric cholesterolazobenzene dimesogen which shows photoresponsive LC, chiral induction, as well as gel formation.…”