A Supramolecular Photonic Crystal Hydrogel Based on Host-Guest Interaction for Organic Molecules Recognition
Host component β-cyclodextrin (β-CD) and guest component tertiary-butyl (t-Bu) were introduced into polymeric backbone material of an inverse opal hydrogel. The association between β-CD and t-Bu functions as an openable cross-linker (“lock”) in hydrogel. Meeting a competitive guest as the target molecule, 1-admantanecarboxylic acid sodium salt (AdCANa) acts as a “key” to dissociate the pair of β-CD and t-Bu due to its stronger combination capacity with the β-CD than the t-Bu. At the same time, another cross-linker N,N-methylenebisacrylamide (MBAAm) provides covalent bonds to the backbone material, ensuring the subsequent association/dissociation between the host-guest pair only results in an expansion-contraction in volume, rather than a sol-gel phase transition. In this way, the target molecule acting as a competitive guest can cause expansion-induced structural color change of the inverse opal hydrogel. Following the same strategy, the L- and D-enatiomers of tryptophan (Try) can also be recognized. The combination between the supramolecular host-guest pair and photonic crystals promises applicability in molecular recognition and other interesting optical devices.