Selective Turn-On Ammonia Sensing Enabled by High-Temperature Fluorescence in Metal–Organic Frameworks with Open Metal Sites

Abstract

We show that fluorescent molecules incorporated as ligands in rigid, porous metal-organic frameworks (MOFs) maintain their fluorescence response to a much higher temperature than in molecular crystals. The remarkable high-temperature ligand-based fluorescence, demonstrated here with tetraphenylethylene- and dihydroxyterephthalate-based linkers, is essential for enabling selective and rapid detection of analytes in the gas phase. Both Zn2(TCPE) (TCPE = tetrakis(4-carboxyphenyl)ethylene) and Mg(H2DHBDC) (H2DHBDC(2-) = 2,5-dihydroxybenzene-1,4-dicarboxylate) function as selective sensors for ammonia at 100 °C, although neither shows NH3 selectivity at room temperature. Variable-temperature diffuse-reflectance infrared spectroscopy, fluorescence spectroscopy, and X-ray crystallography are coupled with density-functional calculations to interrogate the temperature-dependent guest-framework interactions and the preferential analyte binding in each material. These results describe a heretofore unrecognized, yet potentially general property of many rigid, fluorescent MOFs and portend new applications for these materials in selective sensors, with selectivity profiles that can be tuned as a function of temperature.

Photoluminescent Metal–Organic Frameworks for Gas Sensing

“…For example, Dincaˇ et al reported two MOFs [Zn 2 (tcpe)(H 2 O) 2 ]·4DEF and [Mg(H 2 dhbdc)(DMF) 2 ] (H 4 tcpe = tetrakis(4‐carboxyphenyl)ethylene, DEF = N , N ‐diethylformamide, H 4 dhbdc = 2,5‐dihydroxybenzene‐1,4‐dicarboxylic acid) showing shifts of emission wavelengths upon interaction with ammonia at 100 °C ( Figure 9 ). 96 [Zn 2 (tcpe)] shows staggered 2D layers constructed from paddle‐wheel shaped Zn 2 (RCOO) 4 clusters linked by tcpe 4− ligands, and is permanently porous with BET surface area of 317 m 2 g −1 . [Mg(H 2 dhbdc)] is constructed from 1D Mg 2 (RCOO) 4 chain linking by H 2 dhbdc 2− linkers in an alternative manner, showing 1D channel about 5.3 × 5.3 Å 2 .…”

Construction of two Cd(II) complexes by flexible adipic acid plus 2-((benzoimidazol-yl)methyl)-1H-tetrazole ligand

“…The rational design and synthesis of complexes have received extensive attentions for their various intriguing architectures and potential applications [1][2][3][4]. Nevertheless, how to reasonably construct the desired structures is still a huge challenge.…”

Tuning Two-Dimensional Layer to Three-Dimensional Pillar-Layered Metal–Organic Frameworks: Polycatenation and Interpenetration Behaviors

“…In recent years, the assembly of metal−organic frameworks (MOFs) has become a very hot research topic because of their intriguing structural features and potential applications in a wide range of research fields such as gas storage/separation, 1−3 catalysis, 4 sensor, 5,6 and biomedical imaging. 7 Several strategies have been suggested for the rational construction of MOFs with desired structures and functions, in which reticular chemistry using the concept of secondary building units (SBUs) is demonstrated most popular and effective for this porpose.…”