Wholly Visible-Light-Responsive Host–Guest Supramolecular Gels Based on Methoxy Azobenzene and β-Cyclodextrin Dimers

Abstract

Much attention has been paid to construct photoresponsive host− guest supramolecular gels; however, red-shifting the responsive wavelength remains a formidable challenge. Here, a wholly visible-light-responsive supramolecular gel was fabricated through the host−guest interaction between a βcyclodextrin (β-CD) dimer and a tetra-ortho-methoxy-substituted azobenzene (mAzo) dimer (binary gelator) in DMSO/H 2 O (V/V = 8/2). The minimum gelation concentration of the low-molecular-weight binary gelator was 6 wt % measured via the tube inversion method. The substituted methoxy groups shifted the responsive wavelengths of trans-mAzo and cis-mAzo to the green and blue light regions, respectively. The host−guest interaction between mAzo and β-CD as the driving force for gelation was confirmed using the 1 H-NMR and 2D 1 H NOESY spectra. The supramolecular gel showed good self-supporting ability with a storage modulus higher than 10 4 Pa. The release of Rhodamine B loaded in the gel as a model drug could be controlled by green light irradiation. We envisioned the potential applications of the wholly visible-light-responsive supramolecular compounds ranging from biomedical materials to smart materials.

Stimuli-responsive cyclodextrin-based supramolecular assemblies as drug carriers

“…Azo derivatives have been employed in CD-based systems. 119,128 Research studies show that the chemical modification of Azo can affect the photo-responsiveness of the material. 129 Compared with the UV-induced isomerization of Azo, the isomerization of tetra-ortho-methoxy-substituted azobenzene (mAzo) occurs under visible light, with high quantum yields and extinction coefficiency.…”

“…110 In a mAzo dimer/CD dimer system, a sol-gel-sol process could be processed via alternant light irradiation, followed by a morphology change. 128 In a layer-by-layer system comprising poly{6-[(2,6-dimethoxyphenyl) azo-4-(2 0 ,6 0dimethoxy)phenoxy]propyl dimethylaminoethyl methacrylaterandom-poly(2-(N,N-dimethylaminoethyl) methacrylate) (mAzo-PDMAEMA)} and polyacrylic acid, the assembly and release of CD modified with rhodamine B were controlled by light irradiation. 110 Later, mAzo-PDMAEMA was combined with poly{6-[(2,6-dimethoxyphenyl)azo-4-(2 0 ,6 0 -dimethoxy)phenoxy] hexyl acrylate-random-acrylic acid} (mAzo-PAA) to construct a visible light-responsive surface with reversible switching between antibacterial and bioadhesive properties.…”

Recent advances in polysaccharide‐based hydrogels for synthesis and applications

“…[235] In addition, the introduction of conductive CNT or graphene could endow hydrogels with near-infrared (NIR) light-responsive property because of the transformation from NIR light to heat. [235,236] Furthermore, CDs can be crosslinked by ECH in alkaline media to form polycyclodextrins, [237][238][239] or dimer, [240] which can act as multifunctional crosslinkers, when mixing with guestcontaining polymers, supramolecular hydrogels are readily obtained through host-guest interactions.…”

Dynamic Wetting of Photo-Responsive Arylazopyrazole Monolayers is Controlled by the Molecular Kinetics of the Monolayer

“…[9][10][11][12] Arylazopyrazoles (AAP) have been recently introduced as a new class of photo-switchable molecules that exhibit advantages over existing systems. [13][14][15][16] Similar to azobenzenes, 9,12,[17][18][19] AAPs can change their E/Z configuration by photoisomerization using 520 nm visible or 365 nm UV light, [20][21][22] but are considered as superior analogues to azobenzene derivatives because of their high photostationary states of >90% for switching in both directions and their remarkably long thermal half-life times. 18,23,24 Depending on the system under investigation, the light-induced changes of the contact angle Θ vary to a large extend.…”