Isostructural Single- And Dual-Lanthanide Metal–Organic Frameworks Based On Substituent-Group-Modifying Tetracarboxylate Ligands for Ratiometric Temperature Sensing

Abstract

In this study, two substituent-group-modifying tetracarboxylate ligands, 2',5'-dimethoxy-[1,1':4',1″-terphenyl]-3,3″,5,5″-tetracarboxylic acid (H₄TPTC-2OMe) and 2',5'-dimethyl-[1,1':4',1″-terphenyl]-3,3″,5,5″-tetracarboxylic acid (H₄TPTC-2Me), with similar geometries were used as the organic linkers to construct isostructural lanthanide metal-organic frameworks (LnMOFs). The as-prepared LnTPTC-2OMe and LnTPTC-2Me were structurally elucidated by means of single-crystal and powder X-ray diffraction in addition to thermogravimetric analysis and were assessed as luminescence ratiometric thermometers by obtaining the temperature dependence of the luminescence behaviors. We found that both the single lanthanide EuTPTC-2OMe and the dual lanthanide Eu_0.05Tb_0.95TPTC-2Me exhibited a distinct S-type luminescence response to temperatures in the range from 313 to 473 K, and their ratiometric parameters can be understood on the basis of the classic Mott-Seitz model. Energy transfers from the ligand to Tb³⁺ (or Eu³⁺) and from Tb³⁺ to Eu³⁺ in these two systems were investigated theoretically as well as with low-temperature (77 K) time-resolved photoluminescence spectroscopy, quantum yield, and lifetime analysis. Therefore, these two materials possess a good relative sensitivity, a small temperature uncertainty, and a favorable spectral repeatability in addition to a remarkable emission color change, enhancing their potential use for temperature measurement and in situ monitoring in microelectronics.