Metal nanoclusters (NCs) have been engineered as a new kind of luminescent material, whereas the application of metal NCs in aqueous solution was subjected to great limitations owing to their poor solubility, stability, and strong luminescence quenching in a single-molecule state. Herein, facile supramolecular self-assembly strategy was carried out to enhance the luminescence of Ag(I) NCs (Ag-NCs) through multiple electrostatic interactions with polyethyleneimine (PEI). Functional colloid aggregates of Ag-NCs such as nanospheres and nanovesicles were formed along with the enhanced emission because of the formation of compact-ordered self-assemblies, which effectively restricted intramolecular vibration of the capping ligands on Ag-NCs to diminish the nonradiative decay. All those could block energy loss and facilitated the radiative relaxation of excited states which ultimately induced an aggregation-induced emission (AIE) phenomenon. Furthermore, the luminescent Ag-NCs/PEI nanovesicles are pH-responsive and show a superior fluorescent sensing behavior for the detection of Al with a limit of detection low to 3 μM. This is the first report about AIE of silver NCs with polymers in aqueous solution. This work sheds light on the controlled NCs-based supramolecular self-assembly and the NCs-based functional materials, which will be well-established candidates in controllable drug delivery, biomarkers, and sensors in aqueous solution.

The self-assembly of chiral metal nanoclusters into supramolecular chiral aggregates is of interest for developing advanced materials. Herein, we manipulated the self-assembly of Au nanoclusters modified by l-/d-cysteine (l-/d-AuNCs) into ordered microstructures featuring enhanced phosphorescence and optical activities. The formation of these aggregates was driven by synergistic effect of coordination and electrostatic interactions assisted by Cd2+/H+. Detailed structural characterization and theoretical studies confirmed that the compact aggregation structures are essential for the emission enhancement and the chirality amplification of l-/d-AuNCs. Interestingly, upon the formation of microflowers, the emission lifetime was prolonged to 3.34 ms with a switch from fluorescence to phosphorescence induced by aurophilic Au­(I)···Au­(I) interactions and intensive ligand-to-metal charge transfer (LMCT). Moreover, both the CD and photoluminescence (PL) signals of the microflowers exhibited pH-responsiveness. This dual-mode sensitive platform could be developed as a pH sensor with improved accuracy. Additionally, the pH-responsive photoluminescence ON/OFF switch of the microflowers could be employed for reliable information encryption and decryption. This study provides useful ideas for regulating the self-assembly of nanoclusters to generate desired photophysical properties with potential applications.

Supramolecular self-assembly, based on non-covalent interactions, has been employed as an efficient approach to obtain various functional materials from nanometer-sized building blocks, in particular, [Ag(mna)], mna = mercaptonicotinate (Ag-NC). A challenging issue is how to modulate the self-assembly process through regulating the relationship between building blocks and solvents. Herein, we report the controlled self-assembly of hexanuclear silver nanoclusters into robust multilayer vesicles in different solvents, DMSO, CHCN, EG and MeOH. Their unique luminescence enables them to be bifunctional probes to sense Fe and dl-dithiothreitol (DTT). By protonating the Ag-NC to Ag-H-NC using hydrochloric acid (HCl), the multilayer vesicles survive in aprotic solvents, DMSO and CHCN, but are transformed to nanowires in protic solvents, water, EG and MeOH. Our results demonstrated that the solvent-bridged H-bond plays a key role in the evolution of the morphologies from vesicles to nanowires. Moreover, the nanowires could further hierarchically self-assemble in water into hydrogels with high water content (99.5%), and with remarkable mechanical strength and self-healing properties. This study introduces a robust cluster-based building block in a supramolecular self-assembly system and reveals the significance of aprotic and protic solvents for the modulation of the morphologies of cluster-based aggregates.

Polyvinyl alcohol (PVA) hydrogels have been proposed for use as promising biomaterials in biomedical and tissue engineering, and graphene oxide (GO) has been recognized as a unique two-dimensional building block for various graphene-based supramolecular architectures. In this article, we systematically studied the influence of three kinds of PVA with different molecular weights on the interaction between PVA and GO. Moreover, the effects of PVA on the gelation of GO were also investigated. The native PVA hydrogel, as well as PVA-GO hybrid hydrogels, have been thoroughly characterized by the phase behavior study and various techniques including field emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA) and rheological measurements. It can be seen that with the increase of the molecular weight of PVA, the addition of GO can effectively promote the gelation of PVA which can be reflected by a decrease of the critical gel concentration (CGC) for PVA-GO hydrogels. Dye adsorption experiments indicate that the toxic dye, i.e., methylene blue (MB), was efficiently entrapped in the PVA-GO xerogels. It is also demonstrated that the gelation of PVA and GO composites can be promoted by different supramolecular interactions, including hydrogen bonding and electrostatic interaction. This work indicates that the PVA-GO composite is a good candidate for preparing "super" and "smart" hydrogels and will enable further studies on the supramolecular chemistry of PVA, graphene and its derivatives.

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