A multifunctional Tb3+–salicylic acid hydrazide phosphor for anti-counterfeiting, forensic fingerprint visualization, and biological applications

Abstract

Abstract A novel terbium(III) complex, Tb(SAH) , derived from salicylic acid hydrazide ( SAH ), was successfully synthesized and fully characterized. Stoichiometric analysis confirmed a 1:2 metal-to-ligand ratio. X-ray diffraction and microscopic studies revealed a polycrystalline structure with micro- and nanodomain features. Photoluminescence investigations demonstrated intense monochromatic emissions: blue for SAH and green for Tb(SAH) , with relatively long excited-state lifetimes in dimethylformamide (DMF), solid state, and polymeric matrices (PVA (polyvinyl alcohol), PMMA (polymethyl methacrylate), and silica xerogel). An efficient ligand-to-metal energy transfer mechanism under ultraviolet (UV) excitation was confirmed, indicating a strong antenna effect responsible for enhanced luminescence. Both SAH and Tb(SAH) were successfully applied in latent fingerprint visualization, clearly resolving level I–III ridge details on diverse porous, non-porous, and multicolored substrates. Additionally, transparent luminescent security inks prepared from the compounds exhibited excellent storage stability and humidity resistance, highlighting their suitability for anti-counterfeiting applications. Biological evaluation revealed that Tb(SAH) exhibits significantly greater in vitro cytotoxicity against the hepatocellular carcinoma (HepG-2) cell line than the free ligand. Significant antioxidant activity was observed for SAH and Tb(SAH) (IC 50 = 0.38 and 0.78 μM, respectively), surpassing ascorbic acid. The Tb(SAH) complex also exhibited improved antidiabetic activity (IC 50 = 14 μg/mL) compared with SAH (IC 50 = 44 μg/mL), with potency comparable to that of acarbose (IC 50 = 35 μg/mL). Antimicrobial studies indicated marked enhancement upon Tb 3 ⁺ coordination, particularly against Staphylococcus aureus . Molecular docking against DNA gyrase B (PDB ID: 6TCK) supported strong binding interactions, corroborating the experimental antimicrobial findings.