Red-light-responsive cucurbit[8]uril based host-guest interaction enabling the construction of a photoswitchable supramolecular polymeric hydrogel

The development of an aqueous phase host-guest interaction system with combined features of responding to light within the biooptical window, high binding constant and low cytotoxcity is promising to offer a new efficient tool for constructing appealing photoresponsive functional supramolecular assemblies with potential bio-application. This paper presents the construction of a novel red-light-responsive host-guest interaction system based on cucurbit[8]uril (CB[8]) and water soluble azobenzene (AB) derived guests. Upon alternate red light (650 nm) and blue light (420 nm) irradiation, the reversible Z/E photoisomerization of the azo guest could be triggered to enable the system to exhibit distinct photoswitchable host-guest complexation behavior. While the E-isomeric guest could be encapsulated by CB[8] to form a head-to-tail 2 : 2 stoichiometric complex with a high binding affinity (Ka up to 1020 M-3), the Z-isomeric guest could only form a 1 : 1 stoichiometric complex with CB[8]. By introducing such a photoswitchable host-guest binding motif as a supramolecular crosslinker, a polymeric hydrogel featuring red light-controlled gel-sol transformation could be fabricated. In addition, both the molecular building block and the resulting supramolecular crosslinking polymer could reveal low cytotoxicity. These advantages greatly benefit such a host-guest system to be potentially applied in the fabrication of red-light-responsive biofunctional supramolecular assemblies and materials. A red/blue light induced photoswitchable host-guest system based on CB[8] and water soluble low cytotoxic azo derivatives is constructed, enabling the fabrication of supramolecular polymeric hydrogel with red light-induced gel-sol transformation.