Dual-Emission Carbon Dots Prepared from Quinoline Quaternary Ammonium Salts with Multiple Modulations

Carbon dots (CDs) are cutting-edge nanomaterials that hold considerable promise in fields such as bioimaging, optoelectronics, and sensing owing to their distinctive optical characteristics and compatibility with biological systems. Nevertheless, the restricted range of multicolor emissions and the intricate methods required for the synthesis have hindered their wider application. Herein, quinoline quaternary ammonium salts are selected as precursors because of their tunable photoluminescence by charge distribution, conjugate effects, and chemical environments, which are expected to be retained in the CDs. This solves the above problems by presenting dual-emission CDs (DE-CDs) that offer finely adjustable emissions ranging from blue to red fluorescence achieved through straightforward synthesis methods. The two emission bands from core and surface states display sensitivity toward excitation wavelength, concentrations, and solvents. These excellent characteristics enable precise ratiometric sensing for water detection and facilitate multicolor luminescent applications. Notably, DE-CDs retain their unique optical properties in PMMA composites, indicating potential applications in multicolor and solid-state luminous technologies. The insights gained from this work not only contribute to the fundamental understanding of CD luminescence but also lay the groundwork for creating advanced optical devices that feature tunable emission characteristics.