Achieving precise luminescence regulation through manipulating aggregation and protonation in pyrene-based materials

Aggregation-induced emission (AIE) materials have garnered significant interest due to their unique optical properties, unlike traditional fluorophores. The combination of AIE with aggregation-caused quenching (ACQ) materials presents an intriguing avenue for precise regulation of luminescent behavior. However, materials with both AIE and ACQ effects are rarely reported. Herein, a novel pyrene-based double emission AIE material (DE-AIE) is synthesized, which can enable precise luminescence regulation through the manipulation of aggregation states and protonation levels. Specifically, as the volume fraction of the poor solvent water increases, DE-AIE undergoes successively the quenching of green fluorescence caused by π-π stacking between molecules and the enhancement of orange fluorescence due to the restriction of intramolecular motions. In addition, DE-AIE exhibits further red-shifting of the absorption and emission peaks in response to acid, which is attributed to the enhancement of intermolecular charge transfer resulting from the protonation. And the reversible acid-base fluorescence regulation was demonstrated by acid-base cycle experiments. The fluorescence emission peak of DE-AIE after adding acid present an apparent redshifted (116 nm) from that in the dispersed state, endowing a broad wavelength range for regulating luminescence through aggregation and protonation. Furthermore, the relationship between the luminescence mechanism and the intermolecular or intramolecular interactions of materials during aggregation was explored by nuclear magnetic resonance titration experiment. Based on the unique luminescent characteristics, DE-AIE holds significant potential for applications in recyclable molecular “Traffic Signals”, information encryption with multilevel, and visual sensing of multi-gradient humidity.