UV-induced near-white visible emission in dinuclear Tb(iii) complexes: a photophysical, theoretical and computational study on fluxidentate ligand bridging and coordination geometry

Abstract

In this work, three Tb(III) complexes, TbA, TbM and TbD, were synthesized using 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione (TTBD) and pyrazine (pyz) as antenna moieties. Structural characterizations (elemental (CHN), infrared and NMR) confirmed that TbA and TbM are mononuclear and share an identical structural framework, while TbD forms a dinuclear species where pyrazine serves as a bridging ligand. Photoluminescent (PL) features of the complexes were studied through electronic absorption, PL and lifetime analyses. All three complexes emit the characteristic emissive peaks of Tb(III) ions along with a broad ligand-centered band due to the sensitizer energy difference. Upon incorporation of chromophores, the emission color shifts dramatically towards near-white, showcasing tunable optical behavior. The Judd–Ofelt analysis supported these photophysical observations theoretically. Detailed decay studies provided radiative lifetime data and insights into the qualitative energy transfer efficiency from the ligand to the metal. Bandgap analysis using Tauc's method, supported by DFT calculations revealed semiconducting behavior with a value of ∼3.2 eV. These outcomes highlight the possibility of these complexes for use in photonic and optoelectronic applications, highlighting how pyrazine incorporation enables fine-tuning of Tb(III) luminescence to achieve near-white emission.