Bioactive supramolecular carbazate salts and their photoluminescent carbon dots: antibacterial, antioxidant, catalytic, and metal-ion sensing properties

Three novel proton-transfer salts (PE1, PE2, and PE3) were synthesized from pyridine-2,6-dicarboxylic acid and ethyl carbazate and comprehensively characterized using spectroscopic, thermal, crystallographic, and computational techniques. Single-crystal X-ray diffraction (SC-XRD) analysis revealed that PE1 crystallizes in the triclinic P-1 space group, forming a proton transfer-assisted hydrogen-bonded supramolecular framework. Density functional theory calculations demonstrated that PE1 possesses the smallest HOMO-LUMO energy gap, consistent with its superior antibacterial and antioxidant activities, as supported by molecular docking studies and in vitro assays. More importantly, PE1 was employed as a well-defined molecular precursor for the synthesis of fluorescent nitrogen-doped carbon dots via a simple solvent-free pyrolysis route. The resulting carbon dots, with an average diameter of approximately 4.6 nm, exhibited selective Cu²⁺/Ni²⁺ chemosensing and achieved 85.39% catalytic reduction of nitrobenzene, markedly outperforming the molecular precursor. This work introduces a new molecular platform for engineering multifunctional carbon nanomaterials with promising applications in sensing, catalysis, and environmental remediation.