Ion Site Substitution in a Sulfonylcalix[4]arene-Supported Ln₈ (Ln = Tb and Eu) Coordination Wheel with Tunable Luminescence

Lanthanide coordination clusters (LCCs), namely, [Ln8(TC4A-SO2)4(TA)2(DMF)4(H2O)10] (solvents) (Ln8 = Tb8, Eu8, Tb4Eu4; H4TC4A-SO2 = p-tert-butylsulfonylcalix[4]arene; H4TA = dl-tartaric acid), were synthesized via the solvothermal method and were characterized by single-crystal X-ray diffraction. Ln8 is a wheel-shaped framework built from four cone-shaped mononuclear units (LnIII-TC4A-SO2) and four bridging-LnIII ions with two tartrates located in the center serving as “spokes”. Tb8 exhibits an extraordinary luminescence quantum yield (QYs) of 53.3% in the solid state under the excitation of 370 nm, while Eu8 cannot emit under similar conditions. Furthermore, Tb8 shows concentration-dependent emission in a methanol solution with the best luminescence QYl of 61.8%, representing one of the best luminescent Tb-based coordination clusters. The Eu ions can be rationally doped in the Tb ring (TbxEu8–x, 4 ≤ x < 8) by a stoichiometric ratio on specific sites to tune the emission color output, which reveals the efficient energy transfer from 5D4-7F5 and 5D4-7F6 levels of TbIII to the 5D0 level of EuIII. This work presents a unique method of controlling the fabrication and tunable luminescence of LCCs.