Organophosphorus Moieties Govern Opposite Fluorescence Modulation and Synergistically Enhance Copper(II) Affinity of Precursor-Derived Carbon Dots.

Phosphorus doping is widely employed to tune the fluorescence (FL) of carbon dots (CDs); however, how specific phosphorus chemical moieties govern FL intensity remains poorly elucidated. To reveal structure-property relationships at the moiety level, we developed a combinatorial precursor design strategy to precisely synthesize eight precursor-derived CDs with tailored organophosphorus moieties, including triphenylphosphonium and phenylphosphonic acid moieties, or their combination, within a shared polyacrylamide (PAM) backbone. The local organophosphorus microenvironment governs the FL properties of CDs. The sterically bulky triphenylphosphonium moieties rigidify the carbon framework to restrict intramolecular motions, thereby activating crosslink-enhanced emission (CEE) and enhancing absolute quantum yield (QY) by 1.57-fold. Conversely, electron-withdrawing phenylphosphonic acid moieties introduce nonradiative electron trap states that attenuate emission intensity by 16.71%. Notably, phenylphosphonic acid and triphenylphosphonium moieties synergistically enhance the coordination affinity for copper(II) ions (K = 2.92 × 107 M-1), arising from oxygen-donor chelation and steric stabilization. This moiety-level combinatorial precursor strategy enables the rational design of carbon nanostructures with precisely tailored FL and metal-ion affinity capabilities.