Excimer Formation in a Terbium Metal–Organic Framework Assists Luminescence Thermometry

Abstract

Photoluminescent isotypical phosphonate-based metal–organic frameworks, [Ln­(H5btp)]·2H2O [where Ln3+ = Tb3+ (1) or Gd3+ (2) and H8btp = [1,1′-biphenyl]-3,3′,5,5′-tetrayltetrakis­(phosphonic acid)] prepared under solvo­(hydro)­thermal conditions exhibit a three-dimensional supramolecular structure built up from phosphonate linkers bridging Ln3+ ions. Single-crystal X-ray diffraction of 1 revealed hydrogen bonds along the a-axis between the crystallization water molecules and the phosphonate groups. The network features lozenge-shaped tubular channels with intermolecular interactions between adjacent organic ligand molecules. Crystal packing forces bring together two ligand biphenyl groups in a parallel arrangement, forming an excimer. A ratiometric luminescent thermometer operative close to room temperature was built based on the excimer and the 5D4 → 7F5 Tb3+ emissions, exhibiting a maximum relative thermal sensitivity of 1.26%·K–1 and a minimum temperature uncertainty of 0.75 K at 319 K. This performance is similar to that of a thermometer based on the ligand singlet S 2,1 → S 0 and metal 5D4 → 7F5 transitions. Thus, the same MOF material provides two separate temperature data sets. This work shows the possibility of using excimer emissions in ratiometric luminescence thermometry.

Metal–organic framework assembled from erbium and a tetrapodal polyphosphonic acid organic linker

“…4). We note that this compound shares its topological features with the two families of materials previously described by our research group, namely [Tb(H 5 btp)]Á2H 2 O (Ananias et al, 2017)…”

“…A search in the Cambridge Structural Database (CSD) reveals that this type of coordination environment is not very common among lanthanide-based MOFtype materials, with higher coordination numbers being typically preferred. However, for phosphonate-based organic linkers which exhibit some steric hindrance, this low coordination number seems to be more easily attained, as recently reported by us (Ananias et al, 2017). Moreover, this type of coordination sphere is also of crucial importance in the design of effective optical materials since it typically avoids the presence of water molecules directly coordinated to the metal centre.…”

Guiding Rules for Selecting a Nanothermometer

“…In this case, the organic-inorganic molecules can compose a macromolecular crystalline complex through covalent interactions, known as metal-organic frameworks (MOFs). Most of the MOFs developed for thermometry are based on the emission ratio between europium and terbium [105], but several attempts have also been made with alternative sources of luminescence, such as excimer emission instead of Eu 3+ [106], emission of the organic ligand instead of Eu 3+ or Tb 3+ [107], or the use of Dy 3+ [108]. An extensive review on this precise subject was recently published, and provides detailed information on these options [109].…”

A Robust Mixed‐Lanthanide PolyMOF Membrane for Ratiometric Temperature Sensing

“…the correlation coefficient is 0.999, the sensitivity of Eu 0.0025 Tb 0.9975 ‐ BABDC ‐ PBMA membrane is calculated to be 7.59 % per K [23] . Other index for assessing the thermometer performance including the relative thermal sensitivity (S r ), the temperature uncertainty ( δT ) and the repeatability was then determined according to the reported methods [4m, 24] . The maximum relative sensitivity of Eu 0.0025 Tb 0.9975 ‐ BABDC ‐ PBMA membrane is determined to be 3.61 % K −1 at 240 K (Figure S14 and Experimental Section, Supporting Information), ranked one of the highest sensitivity values reported so far (Table S3) [25] .…”