Fabrication of a Luminescent Supramolecular Hydrogel Based on the AIE Strategy of Gold Nanoclusters and their Application as a Luminescence Switch

Gold nanoclusters (AuNCs) have been recognized as an emerging category of inorganic–organic hybrid luminescent materials owing to their ultrasmall size, good biocompatibility, and especially the aggregation-induced emission (AIE) property. Some works have been reported about the AIE property of AuNCs; however, the mechanism is still indistinct. In the present work, we studied the coassembly behavior of thiobarbituric acid-modified AuNCs (TBA-AuNCs) with Zn2+. The coassembly system could not only enhance the emission of AuNCs but also induce the gelation along with the morphology transformation from nanofibers to micron-sized bowknot-like aggregates. Various methods were used to characterize the properties of a hydrogel such as photoluminescent (PL) spectra, morphology, lifetime, and intermolecular interaction. Significantly, time-/temperature-dependent PL spectra as well as morphological evolution monitoring were implemented to analyze the structure–emission property relationship of TBA-AuNCs assembly systems. It is verified that the π–π stacking of ligands, ligand-to-metal charge transition (LMCT), and the orderliness degree of aggregates contribute uniquely to the emission energy/intensity of TBA-AuNCs, which is significant for the comprehension of the AIE nature of nanoclusters. Besides, the gelation and photoluminescence of TBA-AuNCs are sensitive to heating and ethylenediaminetetraacetic acid disodium salt (EDTA-2Na), making the hydrogels promising candidates as smart luminescent switches. This work is of interest for not only providing a versatile methodology for lighting up AuNCs through gelation but also pointing out a way to understand and regulate the emission of AuNCs.