Modulating Luminescence Thermometry of the EuIII/TbIII Pair in Coordination Polymers through Ligand Structure and Lanthanide(III) Molar Ratio

Abstract Accurate temperature sensing at the nanoscale has become a powerful tool to monitor heat dissipation in miniaturized systems, driving the development of noncontact luminescent thermometers with high sensitivity. EuIII/TbIII-based coordination polymers are particularly attractive for thermometry due to their structural tunability, which allows the correlation of structural and electronic parameters with thermometric performance. Herein, we compare the luminescence thermometry of a series of one-dimensional coordination polymers, [Ln(tfa)3(μ-dppeo)]n, [Ln(tfa)3(μ-dppbo)]n, [Ln(hfa)3(μ-dppeo)]n, and [Ln(hfa)3(μ-dppbo)]n (Ln = EuIII, TbIII; tfa–: trifluoroacetylacetonate; hfa–: hexafluoroacetylacetonate; L: [(diphenylphosphoryl)R](diphenyl)phosphine oxide, R = ethyl - dppeo - or butyl - dppbo), focusing on the combined effects of bridge and terminal ligand scaffold as well as lanthanide (LnIII) molar ratio. For each system, the TbIII/EuIII ratio was adjusted to {Tb0.25Eu0.75}n or {Tb0.75Eu0.25}n, enabling systematic evaluation of ratiometric thermometry based on the TbIII 5D4 → 7F5 and EuIII 5D0 → 7F2 emissions. Structural variations induced by the terminal and bridge ligands modulate crystal packing, local coordination microsymmetry, and LnIII–LnIII distances. Coordination polymers with higher TbIII content exhibit enhanced thermometric performance, reaching a maximum relative thermal sensitivity of 5.20% K–1 at 305 K for [Tb0.75Eu0.25(hfa)3(μ-dppbo)]n. The increase of the TbIII amount potentializes the TbIII-to-EuIII energy transfer and enhances the activation energy of the luminescence thermal quenching. These results demonstrate that controlling the ligand scaffold and LnIII molar ratio enables effective modulation of thermal sensitivity and operating range in EuIII/TbIII coordination polymers.