From mononuclear to pyrazine-bridged dinuclear samarium(iii) complexes: role of fluxidentate coordination in luminescent and thermal behavior.

Three Sm(iii)-complexes featuring β-diketone ligand 4,4,4-trifluoro-1-thienyl-1,3-butadionate (TTBD) were studied for their potential as visible-light emitters. Utilizing pyz (pyrazine) as an ancillary ligand, two mononuclear compounds i.e. binary (SmA) and ternary (SmM) along with a dinuclear compound (SmD) were synthesized. Elemental (CHN), IR and NMR analyses confirmed that two complexes (SmA and SmM) are mononuclear with identical structural frameworks, whereas SmD forms a dinuclear species with pyrazine acting as a bridging ligand. The optical band gaps were measured from UV-vis absorption using Tauc's relation corresponding to HOMO-LUMO (Highest Occupied Molecular Orbital-Lowest Unoccupied Molecular Orbital) transitions. Photophysical investigations in solution phase using dichloromethane (DCM) solvent revealed characteristic emissions of Sm(iii) ions under UV excitation, due to 4G5/2 → 6H j (j = 5/2, 7/2, 9/2, 11/2) transitions in visible region. All complexes displayed intense luminescence with notably high lifetimes (0.063 ms), similar to the most efficient Sm(iii)-based emitters reported. Radiative lifetimes and qualitative ligand-to-metal energy transfer (ET) efficiencies were deduced from time-resolved measurements, confirming that TTBD and pyz function effectively as sensitizing ligands. Colorimetric analysis based on emission spectra yielded CIE coordinates indicative of orange-red luminescence, typical of Sm(iii) ions. Correlated color temperature (CCT) values further suggest their suitability as warm-light emitters. thermogravimetric analysis (TGA) revealed thermal stability up to ∼224-231 °C, emphasizing their promise in thermally stable optoelectronic devices.