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 Zn2+-based MOFs, where two structurally similar
tetracarboxylate ligands, 5,5′-(pyrazine-2,5-diyl)­diisophthalic
acid (H4PZDDI) and 5,5′-(pyridine-2,5-diyl)­diisophthalic
acid (H4PDDI), 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 (Eu3+), two types of composites,
DSM@ZnPZDDI and DSM@ZJU-56 and Eu3+@ZnPZDDI and Eu3+@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, Eu3+@ZnPZDDI
and Eu3+@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.