Molecular-level fluorescence engineering in N-doped graphene quantum dots: electronic–interfacial coupling and emergent photophysics

Molecular-level fluorescence behavior in nitrogen-doped graphene quantum dots (N-GQDs) arises from a complex interplay between electronic reconstruction, surface chemistry, and interfacial environmental coupling rather than isolated structural parameters. This review examines how heteroatom integration reshapes π-conjugated networks, defect landscapes, and excitonic relaxation pathways, leading to emergent photophysical regimes that cannot be explained by conventional quantum confinement models alone. Particular emphasis is placed on the dual role of nitrogen and co-dopants in modulating local electronic density, introducing heterogeneous emissive states, and enabling tunable radiative and nonradiative transitions. In parallel, surface functionalization is identified as a dynamic regulator of exciton–interface interactions, where molecular-scale chemical groups and environmental species collectively govern fluorescence stability, sensitivity, and reversibility. The analysis further highlights how interfacial charge transfer, defect-assisted recombination, and coordination-driven processes converge to produce application-dependent fluorescence modulation across sensing, chemiluminescence, and hybrid optoelectronic systems. By integrating recent advances into a unified mechanistic framework, this work establishes molecular fluorescence as an emergent electronic–chemical phenomenon rather than a static material property. Finally, key limitations in predictive control, structural reproducibility, and structure–property decoupling are discussed, outlining future directions toward programmable and application-specific fluorescence engineering in heteroatom-doped GQD systems.

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