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

ABSTRACT 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 × 10 7 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.