Synthesis, characterization and photophysical behaviour of some Tb(III) complexes based on 6,8-dichlorochromone-3-carboxaldehyde as primary ligand

Four green luminescent Tb(III) complexes have been synthesized using a bidentate ligand 6,8-dichlorochromone-3-carboxaldehyde (L) and neutral heterocyclic ancillary ligands. The complexes showed characteristic Tb(III) ion emission bands at 491 nm, 546 nm, 586 nm, and 623 nm, on irradiation with 345 nm. The excellent green luminescence shown by the complexes is due to prominent 5D4→7F5 transition at 546 nm. Three primary ligands and one secondary ligand around the metal ion provide a highly shielded environment, leading to enhanced luminescence properties of synthesized ternary complexes such as quantum yield (ϕTb = 48.76 %); longer lifetime period (τobs = 0.734 ms); intrinsic quantum yield (ηTb = 23.67 %); and radiative rate (KRad = 6.64 × 102 s−1). The ternary complexes deliver higher thermal stability, up to 170 °C.