Smart luminescent nanoclusters with dynamic covalent bond for reversible information encryption.

Luminescent nanoclusters (NCs) have attracted much attention because of their superior photophysical properties; however, the design of dynamic NCs with reversible structural change is highly challenging. Herein, we synthesize a kind of dynamic luminescent NCs through Schiff base crosslinking between triethylenetetramine (TETA) and tannic acid at room temperature. The proposed NCs have an excitation-independent blue emission, and the maximum emission is available at about 458 nm with two excitation centers. Furthermore, the crosslinking degree of the NCs can be effectively adjusted by TETA and their formation is a kinetic-control process. Most importantly, the proposed NCs show a property of pH-controlled reversible depolymerization and polymerization, accompanied by a cyclic "on-off-on" photoswitching, which is directly attributed to pH-stimulated reversible C=N bond cleavage and re-formation. Because of the reversible structure change properties, the dynamic NCs have been well used in reversible information encryption. This new finding provides not only us with a powerful strategy to study the structure-properties relationship of luminescent NCs but also a design idea for constructing smart optical nanomaterials.