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 lanthanidedoped 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 10.6Å.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 Tb^(3+)to Eu^(3+)is thermally activated,with the most important pathway involving the ^(7)F_(1) Eu^(3+)J-multiplet at room temperature.The energy transfer from the antenna to Eu^(3+)was simulated,and it was found that the most important ligand contributions to the rate come from transfers to the Eu^(3+)upper states rather than direct ligand–metal transfer to 5D1 or 5D0.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.