A NIR-responsive azobenzene-based supramolecular hydrogel using upconverting nanoparticles.

To circumvent the need for direct UV excitation in a supramolecular hydrogel composed of an azobenzene-modified poly(acrylic acid) copolymer and deoxycholate-β-cyclodextrin as a crosslinker, we modified this system for use with LiYF4:Tm3+/Yb3+ upconverting nanoparticles, which emit UV light upon NIR excitation. A complete gel-sol transition was observed in 60 minutes upon 980 nm irradiation. No change was observed under similar conditions of a control sample over the same period of time.