Novel {Pb6} wheels based zeolite-type metal-organic framework for wide temperature range and high sensitivity of luminescent thermometer.

The development of luminescent thermometers synchronously exhibiting high sensitivity and stability in a wide temperature range poses significant challenges. Herein, a novel {Pb6} wheels based metal-organic framework (MOF) formulated as [Pb(pyIPA)]·1.2H2O (Pb-pyIPA, H2pyIPA = 4-(pyridin-4-yl)isophthalic acid) was synthesized via a solvothermal procedure. The Pb-pyIPA MOF possesses a new (4,4)-connected zeolite-type structure with dynamic nanotubes modified by {Pb6} wheels. It shows intensive green emission with a long lifetime of 180 ns and maintains 98.5% of its initial emission intensity after immersion in water for 90 days. By contrast, temperature-dependent photoluminescence explorations demonstrate that the emission intensity and lifetime decreased linearly over the temperature range of 298-423 K, achieving a maximal thermal quenching of 93%, relative sensitivity (Sr) of 1.03% K-1 (intensity-based) and 0.97% K-1 (lifetime-based). These values surpass those of most reported MOFs and commercial inorganic phosphors. Mechanism of high temperature sensitivity was explored by the combination of single crystal X-ray diffraction analysis and density functional theory calculations. The diameter of {Pb6} wheel can be reversibly tuned under the stimulation of external temperature (298-400 K), leading to a significant decrease in the electron cloud distribution around the {Pb6} wheels. Thus, both the emission intensity and lifetime can be vastly affected by the dynamic structural transformation. In addition, the stability and reusability of Pb-pyIPA were also investigated, which can maintain high sensitivity under reversible temperature variations between 298 and 423 K for 5 cycles. This study offers a new perspective for balancing the contradiction between high sensitivity and stability of luminescent thermometers in a wide operational temperature range.