A stoichiometric terbium-europium dyad molecular thermometer: energy transfer properties

The optical thermometer has shown great promise for use in the fields of aeronautical engineering, environmental monitoring and medical diagnosis. Self-referencing lanthanide thermo-probes distinguish themselves because of their accuracy, calibration, photostability, and temporal dimension of signal. However, the use of conventional lanthanide-doped materials is limited by their poor reproducibility, random distance between energy transfer pairs and interference by energy migration, thereby restricting their utility. Herein, a strategy for synthesizing hetero-dinuclear complexes that comprise chemically similar lanthanides is introduced in which a pair of thermosensitive dinuclear complexes, cycTb-phEu and cycEu-phTb, were synthesized. Their structures were geometrically optimized with an internuclear distance of approximately 10.6 angstrom. The sensitive linear temperature-dependent luminescent intensity ratios of europium and terbium emission over a wide temperature range (50-298 K and 10-200 K, respectively) and their temporal dimension responses indicate that both dinuclear complexes can act as excellent self-referencing thermometers. The energy transfer from Tb3+ to Eu3+ is thermally activated, with the most important pathway involving the (F1Eu3+)-F-7 J-multiplet at room temperature. The energy transfer from the antenna to Eu3+ was simulated, and it was found that the most important ligand contributions to the rate come from transfers to the Eu3+ upper states rather than direct ligand-metal transfer to D-5(1) or D-5(0). As the first molecular-based thermometer with clear validation of the metal ratio and a fixed distance between the metal pairs, these dinuclear complexes can be used as new materials for temperature sensing and can provide a new platform for understanding the energy transfer between lanthanide ions.