Unprecedented and Readily Tunable Photoluminescence from Aliphatic Quaternary Ammonium Salts

Compounds bearing aliphatic amines can be emissive under appropriate conditions. However, their ionized counterparts, namely, quaternary ammonium salts (QASs), which are widely used as phase-transfer catalysts, ionic liquids, disinfectants, and surfactants, are known as luminescence quenchers and considered nonemissive. Herein, unprecedented intrinsic fluorescence/phosphorescence dual emissions from various QASs are reported, which can be finely regulated by changing the excitation wavelength, alkyl chain length, counterion, and mechanical stimuli. The bright photoluminescence along with distinct afterglow and tunable multicolor emissions enables the application of QAS solids in advanced multimode anticounterfeiting. This finding refreshes the understanding of QASs and may inspire emerging applications based on the utilization of the intrinsic luminescences of QASs. Furthermore, it opens opportunities for the investigation of QAS-related processes and functions via a photophysical approach and affords strong implications for the fabrication of novel nonconventional luminophores.