Chameleon Luminophore for Sensing Temperatures: Control of Metal‐to‐Metal and Energy Back Transfer in Lanthanide Coordination Polymers

Abstract

In the fields of fluid dynamics, aeronautical engineering, environment engineering, and energy technology, it is critical to accurately measure the physical parameters of a material surface. [1] Optoelectronic devices have generally been employed as temperature and pressure sensors. [2] However, their sensing area is limited to a single point on a surface. There is a need to measure entire surfaces and obtain multidimensional data for mapping surfaces. There are high expectations that materials for surface measurements, such as temperature and pressure-sensitive dyes, will overcome this intrinsic limitation of optoelectronic devices.We seek to design temperature-sensitive dyes using luminescent lanthanide complexes. Lanthanide complexes exhibit characteristic luminescence with narrow emission bands (full width at half maximum, fwhm < 10 nm) and long emission lifetimes (> 1 ms), [3] which make them suitable for use in sensing devices. In 2003, Amao and co-workers reported the first temperature-sensitive dye that employed an Eu III complex in a polymer film. [4] Khalil et al. demonstrated the high performance of an Eu III complex for a temperature-sensitive paint (temperature sensitivity: 4.42 % 8C À1 ). [5] We have reported a Tb III complex, Tb(hfa) 3 -(H 2 O) 2 (hfa: hexafluoro acetylacetonato), that is suitable as a temperature-sensing probe since it exhibits effective energy back transfer (BEnT) from the emitting level of the Tb III ion to the excited triplet state of the hfa ligand. [6] Since BEnT depends on the energy barrier of the process, the emission intensity varies with temperature.To improve the thermosensing performance, it is necessary to develop a thermostable structure for high-temperature sensing and to implement a dual sensing unit for a high sensing ability. First, we focused on a lanthanide coordination polymer to produce a thermostable structure. Thermally stable coordination polymers and metal-organic frameworks have been widely studied. [7] Carlos and co-workers recently reported novel three-dimensional lanthanide-organic frameworks with 2,5-pyridinedicarboxylic acid. [8] Marchetti et al. developed thermostable Eu III coordination polymers with 4acyl-pyrazolone ligands. [9] Here, we consider that introducing Tb III ion and hfa ligands to coordination polymer frameworks will produce a Tb III coordination polymer that can be used as a temperature-sensing probe. The triplet state of hfa (22 000 cm À1 ) is very close to the emitting level of the Tb III ion (20 500 cm À1 ), resulting in effective EnT1 and BEnT and thus high-performance thermosensing dyes (Figure 1 a). We also selected low-vibrational frequency phosphane oxide [10] as the linking part in the Tb III coordination polymer because lanthanide complexes with high emission quantum yields composed of hfa and bidentate phosphane oxide ligands have been reported. [11] Second, we attempted to impart ratiometric temperature sensing by using luminescent Eu III and Tb III ions in the frameworks of the coordination polymer to realize a high th...

Seven‐Coordinate Luminophores: Brilliant Luminescence of Lanthanide Complexes with C3v Geometrical Structures

“…[37] The back energy transfer from lanthanide ion to the ligands is enhanced when the energy gap is less than 1850 cm -1 . [38] Therefore, the combination of Tb III with hfa ligand is expected to enhance back energy transfer, resulting in low intrinsic emission quantum yield at room temperature.…”

Thermosensitive Luminescent Lanthanide Complex with Two Photosensitized Ligands

“…(11,12) In our experiment on the temperature dependence of the luminescence intensity, we observed a significant increase in Eu-emission intensity between 300 and 350 K. Therefore, we considered the photosensitized emission mechanism based on hfa and TPO ligands. The excitation spectra of Eu/Tb(hfa) x (TPO) y monitored at 610 nm (Eu: 5 D 0 → 7 F 2 ) and 545 nm (Tb: 5 D 4 → 7 F 5 ) are shown in Fig.…”

“…The emitting level of Tb ( 5 D 4 : 20534 cm −1 ) (17) is close to the triplet level of the hfa ligand (22000 cm −1 ). (11) It is well known that thermal quenching between Tb and hfa occurs easily. In contrast, the combination of Eu and hfa shows little thermal …”

“…Elemental analyses were performed on a J-Science Lab Micro Corder JM 10 and an Exeter Analytical CE440. The ratio of F to Eu was measured using an energy dispersive X-ray fluorescence spectrometer EDX-8000 with the reference material Eu(hfa) 3 (TPPO) 2 , (11) and the Eu/ Tb ratio was measured using ICP-AES Shimadzu ICPE-9000. X-ray diffraction (XRD) patterns were characterized using a Rigaku SmartLab X-ray diffractometer with Cu K α radiation, a D/teX Ultra detector, and a temperature control unit (Anton Paar, TCU-110).…”

“…We also have reported thermosensing materials based on lanthanide coordination polymers. (11,12) Here, we report on a coordination compound composed of lanthanide ions and two different ligands. Eu and Tb mixed coordination compounds using tris(p-carboxyphenyl) phosphine oxide (TPO) and hexafluoroacetylacetonate (hfa: photosensitized ligand) ligands were prepared as thermosensing materials.…”