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

Abstract

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 10.6Å. The sensitive linear temperature-dependent luminescent intensity ratios of europium and terbium emission over a wide temperature range (50–298K and 10–200K, 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 7F1 Eu3+ 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 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.

One‐Step Synthesis of Mixed Lanthanide Metal–Organic Framework Films for Sensitive Temperature Mapping

“…The plot of the relative sensitivity against temperature in Figure e reveals maximum relative sensitivity of 16.14% K −1 at 359 K. Notably, a high S r of 9.01% K −1 at 353 K was also attained over the physiological temperature range (293–353 K), which outperforms existing luminescence thermometers in this temperature range (Table S2, Supporting Information) …”

The design of responsive luminescent lanthanide probes and sensors

“…For example, Tb* to Eu energy transfer occurs in the solid state 55,56 and in solution, and can be controlled in well-designed series of heterodinuclear complexes. 57 In a dinuclear system with the Tb and Eu ions believed to be separated by 10.6 Å, it has been found that energy transfer from Tb 5 D 4 to Eu 7 F 1 was most efficient and was thermally activated. Earlier work had shown that if the transitions are not exactly at resonance, for a Förster transfer mechanism the energy difference must be conserved by phonons.…”

Mono- and Mixed Metal Complexes of Eu3+, Gd3+, and Tb3+ with a Diketone, Bearing Pyrazole Moiety and CHF2-Group: Structure, Color Tuning, and Kinetics of Energy Transfer between Lanthanide Ions

“…The relative proximity of the excited state energies of Eu 3+ (~17,240 cm er1 ) and Tb 3+ (~20,400 cm −1 ) and the relatively small metal-to-metal distances in most common structures [ 51 ] cannot only provide two independent luminescence processes for each of the ions but also allow the transfer of excitation energy from Tb 3+ ions to Eu 3+ . The thermal dependence of the efficiency of such transfer mainly determines the working mechanism of “luminescent thermometers” [ 52 ].…”

“…Second, quite often, the luminescence excitation spectra of Eu 3+ contain peaks corresponding to the excitation of Tb 3+ ions [ 10 , 51 ]. Third, introducing Eu 3+ ions reduces the lifetimes of the excited state of terbium(III) ions significantly [ 52 ]. Finally, in a number of cases, decay curves of Eu 3+ are not described satisfactorily by usual single- or biexponential models but contain the initial growth period [ 10 ].…”