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

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 beta-cyclodextrin (beta-CD) dimer and a tetra-ortho-methoxy-substituted azobenzene (mAzo) dimer (binary gelator) in DMSO/H2O (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 beta-CD as the driving force for gelation was confirmed using the H-1-NMR and 2D H-1 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.