Manal A. Rawashdeh-Omary

On/off luminescence vapochromic selective sensing of benzene and its methylated derivatives by a trinuclear silver(I) pyrazolate sensor.

{[3,5-(CF(3))(2)Pz]Ag}(3) (1) films exhibit selective/reversible sensing of small-organic-molecule (SAM) vapors, which readily switch-on bright-green (benzene or toluene) or bright-blue (mesitylene) luminescence that switches-off upon vapor removal. Vapors of electron-deficient SAMs or non-aromatic solvents did not attain luminescence switching and were not adsorbed.

Golden Metallopolymers with an Active T1 State via Coordination of Poly(4-vinyl)pyridine to Pentahalophenyl-Gold(I) Precursors

Brightly phosphorescent gold-based metallopolymers have been synthesized by reaction of nonluminescent reactants comprised of the commercially available polymer PVP = poly(4-vinylpyridine) and the Au(I) precursors [Au(C(6)X(5))THT] (X = F or Cl; THT = tetrahydrothiophene). The metallopolymer products exhibit remarkable photoluminescence properties including high solid-state quantum yield (up to 0.63 at RT) and coarse- and fine-tuning to multiple phosphorescence bands across the visible spectrum via luminescence thermochromism and site-selective excitation. The emissions are caused by intrachain and interchain aurophilic interactions between the linear Au(I) complexes in the metallopolymers. This investigation provides further manifestations of interesting chemistry and photophysics in N-heterocyclic coordination compounds of Au(I) by expansion from the small-molecule to the metallopolymer regime. The spectroscopic and material properties of the new class of metallopolymers are desirable for future studies that will utilize them as emitters for photonic applications such as polymer light-emitting diodes and sensors.

Electronic structure studies of six-atom gold clusters

the @Au6~PPh3!6# unit of 1 carries a 12 charge, that the Au6 portion is essentially neutral. More direct evidence for this distribution of the ionized charge has been obtained from HF and DFT calculations of the double ionization energies of models of 1. It is found that the energy required to remove two electrons from a bare Au 6 cluster is much larger than that from an Au 6 cluster with phosphine ligands present; this is again consistent with the 12 charge in 1 being delocalized onto the triphenylphosphine ligands. It is possible that this delocalization of positive charge is responsible for facilitating the adhesion of the gold cluster as finely dispersed particles onto the metal oxide support.

Trinuclear Copper(I) and Silver(I) Adducts of 4-Chloro-3,5-bis(trifluoromethyl)pyrazolate and 4-Bromo-3,5-bis(trifluoromethyl)pyrazolate

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.

Remarkable Alteration of Photophysical Properties of Cyclic Trinuclear Complexes of Monovalent Coinage Metals upon Interactions with Small Organic Molecules

Interaction of cyclic trinuclear complexes of Au(I), Ag(I), and Cu(I) with vapor, liquid, or solid forms of small organic molecules leads to remarkable photophysical changes from those of the parent complex. The luminescence changes are generally attributed to alteration of the intertrimer metal-metal interactions that become perturbed by the organic molecule. In some instances, as manifest by interaction of {[3,5-(CF3)2Pz]Ag}3 with benzene and its alkylated derivatives, the luminescence signal was turned on due to exciplex formation as the non-luminescent trimer becomes brightly phosphorescent when the organic vapor is introduced or when crystals are grown from solutions in the aromatic solvent. A second instance was manifest by luminescence color change from blue for [Au(μ-C2,N3-bzim)]3 (bzim = 1-benzylimidazolate) or green for [Au(μ-C(OEt) = N(ρ-C6H4CH3)]3 to yellow phosphorescence upon their interaction with octafluoronaphthalene due to the latters triplet state that becomes sensitized by a strong gold heavy atom effect. Likewise, various Cu(I) complexes {[3,5-(R,R′)Pz]Cu}3 alter the metal-centered phosphorescence characteristic of each solid to remarkable emission colors that can be tuned across the entire visible region in glassy matrices of various organic solvents. Finally, the phosphorescent emissions of the same aforementioned trimers [Au(μ-C(OEt) = N(ρ-C6H4CH3)]3 and [Au(μ-C2,N3-bzim)]3 undergo complete quenching upon interaction with vapors of the Lewis acidic C6F6 molecule and the strong organic acceptor TCNQ due to disruption of the intertrimer aurophilic interaction and electron transfer, respectively.

External heavy-atom effect of gold in a supramolecular acid-base π stack

The nucleophilic trinuclear Au(I) ring complex Au3(p-tolN=COEt)3, 1, forms a sandwich adduct with the organic Lewis acid octafluoronaphthalene, C10F8. The 1.C10F8 adduct has a supramolecular structure consisting of columnar interleaved 1 ratio 1 stacks in which the Au3(p-tolN=COEt)3 pi-base molecules alternate with the octafluoronaphthalene pi-acid molecules with distances between the centroid of octafluoronaphthalene to the centroid of 1 of 3.458 and 3.509 A. The stacking with octafluoronaphthalene completely quenches the blue photoluminescence of Au3 (p-tolN=COEt)3, which is related to inter-ring Au-Au bonding, and leads to the appearance of a bright yellow emission band observed at room temperature. The structured profile, the energy, and the lifetime indicate that the yellow emission of the 1.C10F(8) adduct is due to monomer phosphorescence of the octafluoronaphthalene. The 3.5 ms lifetime of the yellow emission of 1.C10F8 is two orders of magnitude shorter than the lifetime of the octafluoronaphthalene phosphorescence, thus indicating a strong gold heavy-atom effect. The diffuse-reflectance spectrum of the solid adduct shows new absorptions that are red-shifted from the absorptions of the monomeric organic and inorganic components alone, indicating charge transfer. Luminescence excitation spectra suggest that these new absorptions represent the major excitation route that leads to the yellow luminescence of 1.C10F8, which is different from the conventional heavy-atom effect in which the phosphorescence route entails simply the enhancement of the S1-T1 intersystem crossing of the organic compound.

New Coordination Polymers of Copper(I) and Silver(I) with Pyrazine and Piperazine: A Step Toward “Green” Chemistry and Optoelectronic Applications

Five coordination polymers and one hexanuclear cluster have been obtained, and their crystal structures were determined upon reaction of Cu(I) or Ag(I) precursors with pyrazine (Pyz) or piperazine (Ppz). Five complexes are mixed-imine-ligand with anionic-fluorinated pyrazolate [3,5-(CF3)2Pz]- ([PzF]-) besides Pyz or Ppz, whereas the sixth had the neutral diimine as a single chromophore. Complexes 1-3 are isomers of the same Cu/PzF/Pyz composition with the same or different unit cell stoichiometry, namely, {Cu6[3,5-(CF3)2Pz]6(Pyz)3(CH2Cl2)}∞ (1·CH2Cl2), {Cu2[3,5-(CF3)2Pz]}2(Pyz)2·toluene}∞ (2·toluene), and {Cu3[3,5-(CF3)2Pz]3(Pyz)1.5·1.5benzene}∞ (3·1.5benzene), respectively. Altering only the metal attains {Ag6[3,5-(CF3)2Pz]6(Pyz)2·2benzene} (4·2benzene), while also changing the neutral diimine attains {Ag2[3,5-(CF3)2Pz]2(Ppz)}∞ (5). Using Pyz without an anionic imine yields {[Cu(Pyz)(MeCN)2][BF4]}∞ (6). The crystal structure of 1 shows two trimers linked together with two pyrazine ligands. Crystals of 2 represent a metal-organic framework (MOF-TW1) with significant surface area (1278 m2/g) and porosity (23.7% void volume) without considering toluene adsorbates in channels. MOF-TW1 was obtained serendipitously upon a reaction attempt to attain a mixed-metal product, instead attaining a Cu(I)-only product with interconnected four-coordinate dinuclear units. Likewise, 3 was obtained through a transmetalation of all Ag atoms in 4 to replace them by Cu atoms. Three reactions (to obtain 1, 4, and 5) were successfully carried out by both solvent-mediated and solventless transformations, whereas 2 and 3 were obtained only by solvent-mediated reactions, while 6 was attainable only by solventless transformations. The solventless transformations occurred either by sublimation and vapor diffusion or by mechanical grinding at ambient laboratory conditions-without the aid of heating, high pressure, vacuum, or any automated equipment. All transformations could be monitored by the human eye as the reaction progresses, as evidenced by progressive discoloration and/or luminescence changes. All crystal structures were obtained with the aid of conventional crystal growth methods from organic solvents for bulk products obtained from both solvelntless and solvent-mediated reactions. Powder X-ray diffraction was used to compare bulk products with one another and the crystallographic products. All Cu(I) products are colored and nonluminescent; the progress of their vapor diffusion-based solventless reactions can be followed by gradual discoloration of white solid reactants and/or quenching precursors phosphorescence. Both Ag(I) products were colorless with 4 being luminescent but not 5.