Designing of emerald terbium (III) ions with β-ketocarboxylic acid and heterocyclic ancillary ligands for biological and optoelectronic applications.

A green and highly efficient grinding method was adopted to synthesize emerald terbium complexes with 1-cyclopropyl-6-fluro-4-oxo-7-piperazin-1-ylquinoline-3-carboxylic acid as the main organic ligand and 2,2'-bipyridyl, 1,10-phenanthroline, neocuproine, 5,6-dimethyl-1,10-phenanthroline and bathophenanthroline as ancillary ligands. Structural analysis of these complexes was executed via elemental, infrared and 1 H-nuclear magnetic resonance analysis, which confirmed that the ligand coordinated to the metal ion through β-ketone and hydroxyl groups of carboxylic acid. Thermal stability of these complexes was investigated by study of thermogravimetric/derivative thermogravimetric analysis. Photoluminescence properties were investigated by observing emission spectra (400-700 nm), excitation spectra (250-500 nm) and decay time curves for display devices. The emission spectra revealed that an intense peak at 545 nm was observed due to 5 D4 →7 F5 electronic transition, which is responsible for the emerald colour in synthesized complexes, under 353 nm ultraviolet light excitation. The energy band gap and refractive index were determined, which proclaimed the dormant applications of these complexes in semiconductors. Commission Internationale de l'éclairage colour coordinates confirmed that the emerald emission of these complexes lies in the green region. Furthermore, antioxidant, antimicrobial and antimalarial assays of these complexes were also investigated, which confirmed that these complexes are potent for antioxidant, antimicrobial and antimalarial activities.