Water-and Oxygen-Tolerant Phosphorescent Carbon Nitrides Enable Visual Hydrogel Biosensing

Abstract

Metal-free room-temperature phosphorescent (RTP) materials in aqueous environments offer promising applications due to their long lifetimes and large Stokes shifts but face challenges in stability against water and oxygen. To address this, we developed a trinity strategy that integrates efficient emissive units, excited-state stabilization, and protection from quenching agents within a single polymeric carbon nitride (CN) macromolecule functionalized with imidazolium. This approach yields homogeneous RTP materials exhibiting robust phosphorescence in water and oxygen, with lifetimes up to 80 ms and high quantum yields. Mechanistic studies reveal that incompletely condensed residues enable efficient intersystem crossing, stabilization by the rigid CN framework and hydrophobic microenvironment from covalent imidazolium functionalization. Leveraging these properties, we fabricated a phosphorescent hydrogel for visual detection of Fe 3+ in human serum. This work demonstrates the potential of engineered carbon nitride as a versatile platform for stable, water/oxygen-tolerant organic RTP materials suitable for biosensing applications.