Syntheses, structural, and photoluminescence properties of {[4-X-3,5-(CF3)2Pz]M}3 (X = Cl or Br, M = Cu or Ag) containing a heavier halide at the pyrazolyl ring 4-positions are reported. The Cu2O and Ag2O react with [4-Cl-3,5-(CF3)2Pz]H or [4-Br-3,5-(CF3)2Pz]H to form the corresponding metal pyrazolates, which are trinuclear adducts of the type {[4-X-3,5-(CF3)2Pz]M}3 with a nine-membered M3N6 metallacyclic core. They also feature relatively short M···Cl or M···Br intertrimer separations (∼ 3.6 Å) leading to supramolecular aggregates in the solid state. Distinct from the 4-H analogues {[3,5-(CF3)2Pz]M}3, none of the four complexes described herein exhibits short intertrimer metal-metal interactions (as closest such M···M separations are at a distance greater than 5.0 Å). The {[4-X-3,5-(CF3)2Pz]M}3 adducts exhibit bright photoluminescence even at room temperature. The photophysical data suggest that the {[4-X-3,5-(CF3)2Pz]Cu}3 complexes emit from an associative excited state, and the drastic Stokes shift suggests a significant change to the ground state structure of the trinuclear moiety and/or intermolecular interactions upon photoexcitation. The {[4-X-3,5-(CF3)2Pz]Ag}3 complexes emit from a ligand-centered excited state affected by silver and the heavier halogens. Thin films of {[4-X-3,5-(CF3)2Pz]Cu}3 trimers are promising for volatile organic compound (VOC) sensor applications as they exhibit luminescence color change upon exposure to vapors of benzene and its alkylated derivatives.

The π-acidic, trinuclear, copper(i) pyrazolate {[3,5-(CF3)2Pz]Cu}3 reacts with simple π-basic aromatic hydrocarbon compounds forming sandwich complexes of various types.

Two photochromic mixed fulgide single crystal systems showing multicolor photochromism and enhanced fatigue resistance were prepared with isostructural molecular pairs containing methyl-chloro and methyl-bromo groups. Parent crystals p-methylacetophenylisopropylidenesuccinic anhydride (1E), p-chloroacetophenylisopropylidenesuccinic anhydride (2E), and p-bromoacetophenylisopropylidenesuccinic anhydride (3E) showed light magenta, brownish orange, and orange colors, respectively, upon irradiation at 365 nm. Each two component mixed crystal MIX-1E and MIX-2E composed of 1E/2E and 1E/3E in a 0.39:0.61 and 0.88:0.12 ratio, showed four different colors upon irradiation with UV light and visible light of appropriate wavelengths. Further, it was found that colors of mixed crystals can be fine-tuned to impart different shades of colors over a range of four distinct colors shown by each, upon changing the length of the time irradiated at selected wavelengths. Such multicolored photochromic systems can be used to develop optoelectronic devices upon further improvements.

A metal organic framework, MOF‐199, has been synthesized under solvothermal conditions. Powder X‐ray diffraction (PXRD) pattern, Fourier‐transform infrared spectra (FT‐IR) and scanning electron microscopic images (SEM) confirmed the formation of the expected MOF‐199 structure. The semiconductor properties of MOF‐199 were then fine‐tuned by introducing three benzene derivatives as guest molecules (aniline, m‐aminobenzoic acid and p‐benzoquinone). Modified MOF‐199 samples were characterized using PXRD and FT‐IR. Mott‐Schottky analysis and solid‐state UV‐visible spectroscopy were used to investigate the semiconductor properties of these materials. Once MOF was modified with benzene derivatives, slight changes in d spacing values of PXRD patterns and appearance of new peaks in FT‐IR spectra were observed. The Mott‐Schottky analysis of modified MOF‐199 demonstrated an enhancement in the carrier concentration up to 83 % and a negative potential shift of the flat band potential compared to pure MOF‐199, indicating a higher degree of band bending. According to the solid‐state UV‐visible spectra, doping with organic molecules reduced the bandgap in modified MOF‐199. Thus, this study evidently showcases the potential of fine‐tuning the semiconductor properties of a MOF according to the requirement that allows a single MOF to be utilized in a variety of applications with a simple modification.

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