Hydrogel Lasers Via Supramolecular Host-Guest Complexation

Supramolecular host-guest complexes are dynamic systems composed of typically macrocyclic host molecules encapsulating smaller guest molecules. One of their applications is the selective encapsulation of fluorescent dye molecules to tackle quenching and photobleaching in solution. When extended to solid matrices, the efficiency of dyes can be especially poor, limiting their use in fluorescence-based applications. Here it is demonstrated that supramolecular host-guest complexation in a hydrogel network allows readily tunable hydrogel-based lasers. Poly(N-isopropylacrylamide)-based copolymer hydrogel is used with covalently linked Rhodamine B molecules. By controlled doping of cucurbit[7]uril as a host molecule in the hydrogel, it is shown that the fluorescent quantum yield increases from 17% to 51%, accompanied by 15-fold enhancement in photostability. As proof of concept, a thin-film distributed feedback hydrogel laser with wavelength tunability is fabricated. The results reveal a 30% increase in slope efficiency in the presence of host molecules. These results, combined with the inherent stimuli-response of hydrogels, enable new possibilities for affordable and small-scale photonic devices capable of safely interacting with the environment in, for example, sensing applications.