Breathing Europium–Terbium Co-doped Luminescent MOF as a Broad-Range Ratiometric Thermometer with a Contrasting Temperature–Intensity Relationship

Solvothermal reactions of lanthanide salts and a semirigid tripodal H 3 tatab (4,4',4″- s -triazine-1,3,5-triyltri- p -aminobenzoic acid) ligand in mixed water and N -methyl pyrrolidone (NMP) generated novel breathing MOFs [Ln(tatab)]·solvent (Ln = Eu in 1 -Eu, Tb in 1 -Tb, Eu 0.015 Tb 0.985 in 1 -Eu 0.015 Tb 0.985 ). The framework of 1 was contracted upon removal of guests to form partly desolvated [Ln (tatab)]·3.7H 2 O·2.5NMP ( 1' ). Single-crystal X-ray analyses demonstrated that 1 has the breathing ability to spontaneously release guests and maintain the same topology. In contrast to as-synthesized 1 , the cell volume of 1' decreased markedly upon removal of the guests. Different from linear dicarboxylates, the semirigid tripodal tatab ligand is bridged to an inorganic Ln-O chain, limiting the rotation around the O-O-axis of carboxylate. The breathing mechanism is based on the flexible C-N-C angles of amide bonds in the tatab ligand, causing a change in the solvent-accessible volume in the framework. Interestingly, the luminescence color of breathing co-doped lanthanide MOF 1' -Eu 0.015 Tb 0.985 is blue-shifted and turned from orange to green with an increase in temperature, which can be attributed to a change in the relative intensity of Tb and Eu emissions, and is quite different from that observed for the reported related compounds. The breathing co-doped lanthanide MOF 1' -Eu 0.015 Tb 0.985 can be applied as a high-sensitivity ratiometric thermometer in a broad temperature from 90 to 300 K.