Abstract
A novel Zn(II) metal-organic framework [Zn4O(C30H12F4O4S8)3]n, namely ZnBPD-4F4TS, has been constructed from a fluoro- and thiophenethio-functionalized ligand 2,2′,5,5′-tetrafluoro-3,3′,6,6′-tetrakis(2-thiophenethio)-4,4′-biphenyl dicarboxylic acid (H2BPD-4F4TS). ZnBPD-4F4TS shows a broad green emission around 520 nm in solid state luminescence, with a Commission International De L’Eclairage (CIE) coordinate at x = 0.264, y = 0.403. Since d10-configured Zn(II) is electrochemically inert, its photoluminescence is likely ascribed to ligand-based luminescence which originates from the well-conjugated system of phenyl and thiophenethio moieties. Its luminescent intensities diminish to different extents when exposed to various metal ions, indicating its potential as an optical sensor for detecting metal ion species. Furthermore, ZnBPD-4F4TS and its NH4Br-loaded composite, NH4Br@ZnBPD-4F4TS, were used for proton conduction measurements in different relative humidity (RH) levels and temperatures. Original ZnBPD-4F4TS shows a low proton conductivity of 9.47 × 10−10 S cm−1 while NH4Br@ZnBPD-4F4TS shows a more than 25,000-fold enhanced value of 2.38 × 10−5 S cm−1 at 40 °C and 90% RH. Both of the proton transport processes in ZnBPD-4F4TS and NH4Br@ZnBPD-4F4TS belong to the Grotthuss mechanism with Ea = 0.40 and 0.32 eV, respectively.
Highlights
The luminescent metal-organic framework (LMOF) is a fascinating class of functional materials that has been extensively researched for its inspiring application in plentiful areas, especially chemical sensing of molecules and cation and anion species [1,2,3,4]
The luminescent and sensing property of LMOFs is related to original metal ions, functional ligands and self-assembly processes
LMOF-based sensors have mainly focused on lanthanide-based (e.g., Eu3+, Tb3+ ) metal-organic frameworks largely because of their strong photoluminescence derived from the ligand-to-lanthanide antenna effect [5,6,7,8]
Summary
The luminescent metal-organic framework (LMOF) is a fascinating class of functional materials that has been extensively researched for its inspiring application in plentiful areas, especially chemical sensing of molecules and cation and anion species [1,2,3,4]. The high cost and almost unalterable emission wavelength of lanthanide LMOFs motivate researchers to develop LMOFs using transition metal ions (e.g., Zn2+ , Cd2+ , etc.) as metal nodes [9,10,11]. As some d10 metal ions (e.g., Zn2+ ) are proposed to exert less influence on the emission of LMOFs, ligand design is important for designing Zn-LMOF phosphors [12,13,14]. Metal ion detection has been focused on extensively because excess use and emission of metal species have caused many issues, such as environmental pollution, health hazards, etc.
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