Construction and characterization of rare earth complexes for efficient emission tuning by tetraethyl ethylenebisphosphonate and tridentate chelating nitrogen ligands

Lanthanide nitrate and tetraethyl ethylenebisphosphonate reacted with TPY (1-9) and TPTZ (10-12) in an acetonitrile-ethanol mixture (1-9) and an acetonitrile-methanol mixture solution (10-12), respectively, to synthesize twelve new lanthanide complexes: {[Ln(NO₃)₃TPY]₂L} (Ln = La (1), Ce (2), Pr (3), Nd (4), Sm (5), Eu (6)), {[Ln(NO₃)₃TPY]₂L}·2CH₃CN (Ln = Gd (7), Tb (8), Dy (9)), {[Ln(NO₃)₃TPTZ]₂L} (Ln = Eu (10), Sm (11), Tb (12)) (L = tetraethyl ethylenebisphosphonate; TPY = 2,2':6',2''-terpyridine; TPTZ = 2,4,6-tri(2-pyridyl)-<i>s</i>-triazine). For complexes 1-10, single crystals were obtained. The structures of complexes 1-10 were determined using single-crystal X-ray diffraction. Additionally, these complexes were characterized through infrared spectroscopy, elemental analysis, luminescence studies, thermogravimetric analysis, powder X-ray diffraction, and THz spectroscopy. Structural analysis showed that complexes 1-10 were all ten-coordinated, and their single molecules formed a three-dimensional stacked structure through a variety of intramolecular hydrogen bonds, intermolecular hydrogen bonds and π⋯π stacking. The emission spectra of complexes 5 and 11, 6 and 10, 8 and 12 showed characteristic emission peaks of Sm³⁺, Eu³⁺ and Tb³⁺, respectively. Complex 6 had high quantum yields and long luminescence lifetimes. Furthermore, the synthesized complexes exhibit higher quantum yields and longer luminescence lifetimes when TPY is used as the nitrogen ligand, compared to those using TPTZ. This suggests potential for developing more efficient light-emitting devices.