Modulating Luminescence Thermometry of the Eu^III/Tb^III Pair in Coordination Polymers through Ligand Structure and...

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. Eu^III/Tb^III-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 = Eu^III, Tb^III; 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 (Ln^III) molar ratio. For each system, the Tb^III/Eu^III ratio was adjusted to {Tb_0.25Eu_0.75}_n or {Tb_0.75Eu_0.25}_n, enabling systematic evaluation of ratiometric thermometry based on the Tb^III 5D₄ → ⁷F₅ and Eu^III 5D₀ → ⁷F₂ emissions. Structural variations induced by the terminal and bridge ligands modulate crystal packing, local coordination microsymmetry, and Ln^III-Ln^III distances. Coordination polymers with higher Tb^III content exhibit enhanced thermometric performance, reaching a maximum relative thermal sensitivity of 5.20% K^-1 at 305 K for [Tb_0.75Eu_0.25(hfa)₃(μ-dppbo)]_n. The increase of the Tb^III amount potentializes the Tb^III-to-Eu^III energy transfer and enhances the activation energy of the luminescence thermal quenching. These results demonstrate that controlling the ligand scaffold and Ln^III molar ratio enables effective modulation of thermal sensitivity and operating range in Eu^III/Tb^III coordination polymers.