Tuning the Thermometric Features in 1D Luminescent Eu^III and Tb^III Coordination Polymers through Different Bridge...

Tb^III and Eu^III systems have been investigated as ratiometric luminescent temperature probes in luminescent coordination polymers due to Tb^III → Eu^III energy transfer (ET). To help understand how ion-ion separation, chain conformation as well as excitation channel impact their thermometric properties, herein, [Eu(tfaa)₃(μ-L)Tb(tfaa)₃] one-dimensional (1D) coordination polymers (tfaa^- = trifluoroacetylacetonate, and L = [(diphenylphosphoryl)R](diphenyl)phosphine oxide, R = ethyl - dppeo - or butyl - dppbo) were synthesized. The short μ-dppeo bridge ligand leads to a more linear 1D polymeric chain, while the longer μ-dppbo bridge leads to tighter packed chains. As the temperature rises from 80 K, upon direct Tb^III excitation at 488 nm, the Tb^III emission intensity decreases, while the Eu^III emission intensity increases after 160 and 200 K when L = dppeo or dppbo, respectively. The temperature-dependent emission intensities, due to Tb^III → Eu^III ET, enable the development of ratiometric luminescent temperature probes featuring maximum relative thermal sensitivity up to 3.8% K^-1 (250 K, L = dppbo, excitation at 488 nm). On the other hand, the same system displays maximum thermal sensitivity up to 3.5% K^-1 (323 K) upon ligand excitation at 300 nm. Thus, by changing the excitation channel and bridge ligand that leads to modification of the polymer conformations, the maximum relative thermal sensitivity can be tuned.