Isostructural Single- And Dual-Lanthanide Metal–Organic\nFrameworks Based On Substituent-Group-Modifying Tetracarboxylate Ligands\nfor Ratiometric Temperature Sensing

Abstract

In\nthis study, two substituent-group-modifying tetracarboxylate\nligands, 2′,5′-dimethoxy-[1,1′:4′,1″-terphenyl]-3,3″,5,5″-tetracarboxylic\nacid (H₄TPTC-2OMe) and 2′,5′-dimethyl-[1,1′:4′,1″-terphenyl]-3,3″,5,5″-tetracarboxylic\nacid (H₄TPTC-2Me), with similar geometries were used as\nthe organic linkers to construct isostructural lanthanide metal–organic\nframeworks (LnMOFs). The as-prepared LnTPTC-2OMe and LnTPTC-2Me were\nstructurally elucidated by means of single-crystal and powder X-ray\ndiffraction in addition to thermogravimetric analysis and were assessed\nas luminescence ratiometric thermometers by obtaining the temperature\ndependence of the luminescence behaviors. We found that both the single\nlanthanide EuTPTC-2OMe and the dual lanthanide Eu_0.05Tb_0.95TPTC-2Me exhibited a distinct S-type luminescence response\nto temperatures in the range from 313 to 473 K, and their ratiometric\nparameters can be understood on the basis of the classic Mott–Seitz\nmodel. Energy transfers from the ligand to Tb³⁺ (or Eu³⁺) and from Tb³⁺ to Eu³⁺ in these two\nsystems were investigated theoretically as well as with low-temperature\n(77 K) time-resolved photoluminescence spectroscopy, quantum yield,\nand lifetime analysis. Therefore, these two materials possess a good\nrelative sensitivity, a small temperature uncertainty, and a favorable\nspectral repeatability in addition to a remarkable emission color\nchange, enhancing their potential use for temperature measurement\nand in situ monitoring in microelectronics.