Embedding Red Emitters in the NbO-Type Metal-Organic Frameworks for Highly Sensitive Luminescence Thermometry over Tunable Temperature Range.

The intrinsic advantages of metal-organic frameworks (MOFs), including extraordinarily high porosities, tailorable architectures, and diverse functional sites, make the MOFs platforms for multifunctional materials. In this study, we synthesized two kinds of isostructural NbO-type Zn-based MOFs, where two structurally similar tetracarboxylate ligands, 5,5'-(pyrazine-2,5-diyl)diisophthalic acid (HPZDDI) and 5,5'-(pyridine-2,5-diyl)diisophthalic acid (HPDDI), with pyridine or pyrazine moieties, were employed as the organic linkers. By embedding the red-emitting cationic units of pyridinium hemicyanine dye 4-[p-(dimethylamino)styryl]-1-methylpyridinium (DSM) and trivalent europium ion (Eu), two types of composites, DSM@ZnPZDDI and DSM@ZJU-56 and Eu@ZnPZDDI and Eu@ZJU-56, were harvested and evaluated for use as potential ratiometric temperature probes. The temperature-responsive luminescence of these dual-emitting composites was investigated, and their representative features of relative sensitivity, temperature resolution, spectral repeatability, and luminescence color change were discussed. Importantly, compared with the DSM-incorporated composites, Eu@ZnPZDDI and Eu@ZJU-56 show a much wider sensing temperature range and higher relative sensitivities, suggesting the performance of the composites can be engineered by elaborately combining the host and guest units. Given the rich choices of porous MOFs and emitting units, such a strategy can be useful in the design and preparation of multifunctional dual-emitting sensory materials.