Room-temperature phosphorescence and energy transfer in luminescent multinuclear platinum(II) complexes of branched alkynyls

A series of luminescent branched platinum(II) alkynyl complexes, [1,3,5-{RC[triple bond]C(PEt3)2PtC[triple bond]C-C6H4C[triple bond]C}3C6H3] (R=C6H5, C6H4OMe, C6H4Me, C6H4CF3, C5H4N, C6H4SAc, 1-napthyl (Np), 1-pyrenyl (Pyr), 1-anthryl-8-ethynyl (HC[triple bond]CAn)), [1,3-{PyrC[triple chemical bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}2-5-{(iPr)3SiC[triple bond]C}C6H3], and [1,3-{PyrC[triple bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}2-5-(HC[triple bond]C)C6H3], was successfully synthesized by using the precursors [1,3,5-{Cl(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}3C6H3] or [1,3-{Cl(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}2-5-{(iPr)3SiC[triple bond]C}C6H3]. The X-ray crystal structures of [1,3,5-{MeOC6H4C[triple bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}3C6H3] and [1,8-{Cl(PEt3)2PtC[triple bond]C}2An] have been determined. These complexes were found to show long-lived emission in both solution and solid-state phases at room temperature. The emission origin of the branched complexes [1,3,5-{RC[triple bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}3C6H3] with R=C6H5, C6H4OMe, C6H4Me, C6H4CF3, C5H4N, and C6H4SAc was tentatively assigned to be derived from triplet states of predominantly intraligand (IL) character with some mixing of metal-to-ligand charge-transfer (MLCT) (dpi(Pt)-->pi*(C[triple bond]CR)) character, while the emission origin of the branched complexes with polyaromatic alkynyl ligands, [1,3,5-{RC[triple bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}3C6H3] with R=Np, Pyr, or HC[triple bond]CAn, [1,3-{PyrC[triple bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}2-5-{(iPr)3SiC[triple bond]C}C6H3], [1,3-{PyrC[triple bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}2-5-(HC[triple bond]C)C6H3], and [1,8-{Cl(PEt3)2PtC[triple bond]C}2An], was tentatively assigned to be derived from the predominantly 3IL states of the respective polyaromatic alkynyl ligands, mixed with some 3MLCT (d(pi)(Pt)-->pi*(C[triple bond]CR)) character. By incorporating different alkynyl ligands into the periphery of these branched complexes, one could readily tune the nature of the lowest energy emissive state and the direction of the excitation energy transfer.     

Synthesis,Characterization, Self‐Assembly,Gelation, Morphology and Computational Studies of Alkynylgold(III) Complexes of 2,6‐Bis(benzimidazol‐2′‐yl)pyridine Derivatives

A novel class of alkynylgold(III) complexes of the dianionic ligands derived from 2,6‐bis(benzimidazol‐2′‐yl)pyridine (H₂bzimpy) derivatives has been synthesized and characterized. The structure of one of the complexes has also been determined by X‐ray crystallography. Electronic absorption studies showed low‐energy absorption bands at 378–466 nm, which are tentatively assigned as metal‐perturbed π–π* intraligand transitions of the bzimpy^2? ligands. A computational study has been performed to provide further insights into the nature of the electronic transitions for this class of complexes. One of the complexes has been found to show gelation properties, driven by π–π and hydrophobic–hydrophobic interactions. This complex exhibited concentration‐ and temperature‐dependent ¹H NMR spectra. The morphology of the gel has been characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM).     

Effect of reaction medium on the ionizing radiation-initiated cationic copolymerization of styrene derivatives

The influence of reaction medium polarity on the ionizing radiation-initiated copolymer-ization of styrene derivatives involving unpaired carbocations is examined. In the copo-lymerization of nonpolar monomers such as p-CH3styrene/styrene, a small effect consistent with that predicted by Laidler-Eyring theory is found. In the copolymerization of nonpolar/polar monomer pairs such as p-CH3styrene/p-Clstyrene and styrene/p-Clstyrene, any such effect is masked by specific solvation phenomena. A competition between such phenomena appears to exist, in which the different cations are dominated by different interactions. The p-Clstyryl cation appears to undergo strong intramolecular complexation with the penultimate aromatic ring in nonpolar conditions; thus, this cation displays increased se-lectivity toward monomers best able to disrupt the complex. The p-CH₃styryl and styryl cations do not appear to be subject to such strong complexation; thus, in nonpolar solvent, their selectivity tends towards monomers with the highest cation-solvating ability. The differing copolymerization behavior of the p-Clstyryl cation is consistent with the findings of previous investigations of the effect of reaction medium on chain transfer with these monomers. © 1995 John Wiley & Sons, Inc.     

Insights into molecular chemistry of Chiapas amber using infrared-light microscopy,PIXE/RBS,and sulfur K-edge XANES spectroscopy

Chiapas amber is a natural occurring fossil resin structurally composed of long macromolecule chains with semicrystalline phases associated with both fossil and polymerization process. The most conspicuous characteristic of this fossil polymer is that it preserves ancient organic inclusions. In the present work, PIXE/RBS spectrometry (particle-induced X-ray emission/Rutherford backscattering) were combined with complementary K-edge XANES spectroscopy (X-ray absorption near-edge structure) to identify the amount of sulfur in Chiapas amber. Initially, the amber samples were examined using infrared reflected photomicrography. Amber is transparent to infrared light and so embedded plants and animals are easily visible, showing them in extraordinary detail, as if they were immersed in a water-like solution. The PIXE/RBS data show that the proportion of sulfur in amber is significantly higher than that found in recently formed resins, consistent with the biogeochemical process that transforms the resin into amber during long-term burial in geological deposits. The sulfur K-edge XANES spectra from amber confirm the sulfur abundance and reveal sulfur species in the reduced and intermediate oxidation states in amber. Almost no oxidized sulfur was found, whereas the recent resins show mostly oxidized sulfur fractions. This indicates that labile oxidized sulfur decays during fossilization and resin maturation must occur under conditions of oxygen depletion. The implications of the presence of sulfur in amber for organic preservation is also discussed here. Sulfur compounds work as a polymer additive that promotes intense resin solidification. This restricts the early oxidant-specific biodegradation of the embedded biomatter and, over geological time, provides greater stability against chemical changes.     

Impacts of gold nanoparticle charge and ligand type on surface binding and toxicity to Gram-negative and Gram-positive bacteria

Although nanomaterials facilitate significant technological advancement in our society, their potential impacts on the environment are yet to be fully understood. In this study, two environmentally relevant bacteria, Shewanella oneidensis and Bacillus subtilis, have been used as model organisms to elucidate the molecular interactions between these bacterial classes and Au nanoparticles (AuNPs) with well-controlled and well-characterized surface chemistries: anionic 3-mercaptopropionic acid (MPA), cationic 3-mercaptopropylamine (MPNH₂), and the cationic polyelectrolyte poly(allylamine hydrochloride) (PAH). The data demonstrate that cationic, especially polyelectrolyte-wrapped AuNPs, were more toxic to both the Gram-negative and Gram-positive bacteria. The levels of toxicity observed were closely related to the percentage of cells with AuNPs associated with the cell surface as measured in situ using flow cytometry. The NP concentration-dependent binding profiles were drastically different for the two bacteria strains, suggesting the critical role of bacterial cell surface chemistry in determining nanoparticle association, and thereby, biological impact.     

ASBR Applied to the Treatment of Biodiesel Production Effluent: Effect of Organic Load and Fill Time on Performance and Methane Production

The effect of organic matter and fill time on anaerobic sequencing batch reactor (5 L, 30°C, 8-h cycles, 50 rpm) efficiency has been analyzed. Organic matter was increased by the influent concentration. Fill times investigated were in the batch mode and fed-batch followed by batch. In the batch mode organic matter removal were 93%, 81%, and 66% for influent concentration of 500, 1,000, and 2,000 mgCOD/L (0.6, 1.29, and 2.44 gCOD/L.d), respectively. At 3,000 mgCOD/L (3.82 gCOD/L.d) operational stability could not be achieved. Removal efficiency was improved by increasing the fill time, and was 85% for the 1,000 mgCOD/L condition and fill times of 2 and 4 h, and 80 and 77% for the 2,000 mgCOD/L condition and fill times of 2 and 4 h, respectively. Hence, gradual feeding seemed to improve and to smooth the profiles of organic matter and volatile acids along the cycle with 78 to 96 NmLCH₄/gCOD.     

Unprecedented formation of an acetamidate-bridged dinuclear platinum(II) terpyridyl complex-correlation of luminescence properties with the crystal forms and dimerization studies in solution

An [corrected] acetamidate-bridged dinuclear platinum(ii) terpyridyl complex has been isolated in two crystal forms, a red form and a dark form, with different luminescence properties; electronic absorption, emission and (1)H NMR studies revealed the presence of a dimerization process in the solution state.     

Luminescent phosphine gold(I) thiolates: correlation between crystal structure and photoluminescent properties in [R3PAu{SC(OMe)=NC6H4NO2-4}] (R = Et, Cy, Ph) and [(Ph2P-R-PPh2){AuSC(OMe)=NC6H4NO2-4}2] (R = CH2, (CH2)2, (CH2)3, (CH2)4, Fc)

X-ray crystallography shows the gold atoms in [R3PAu{SC(OMe)=NC6H4NO2-4}] (R = Et, Cy, Ph; 1-3, respectively) and [(Ph2P-R-PPh2){AuSC(OMe)=NC6H4NO2-4}(2)] (R = CH2, (CH2)2, (CH2)3, (CH2)4, Fc; 4-8, respectively) are linearly coordinated by phosphorus and thiolate-sulfur; weak intramolecular Au...O interactions are featured in all structures. The smaller ethyl substituents in 1 allow for supramolecular association via Au...S and Au...Au interactions that are not found in 2 and 3, which contain larger phosphorus-bound Cy and Ph groups, respectively. Intramolecular Au...Au interactions are found in the dppm, dppe, dppp, and Fc structures but not in the dppp analogue, for which an anti conformation was found. The structures have been correlated with the results from photophysical study conducted in the solid state. Thus, photoexcitation of 1-7 with lambda > 350 in the solid state and in solution produces green and blue luminescence, respectively. The spectra in each medium are remarkably similar to each other, and so the emission energy and excitation maxima observed for 1-7 appear to be independent of the nature of the ancillary phosphines, as well as the presence or absence of Au...Au interactions, either intermolecularly or intramolecularly.