Delocalization in platinum-alkynyl systems: a metal-bridged organic mixed-valence compound

A complex featuring two triarylamine redox centers bridged by Pt, trans-bis(triethylphosphine)-bis{4-[bis(4-methoxyphenyl)amino]phenylethynyl} platinum(II), has been synthesized as a model system for pi-conjugated Pt-containing polymers. Analysis of the intervalence charge-transfer band displayed by its mixed-valence monocation affords a quantitative assessment of electronic delocalization through the Pt bridge; this is found to be only slightly smaller than that determined for a benzene-bridged analogue. These results are supported by density functional theory calculations, which show that the active orbitals involved in the electron-transfer process in both cases have similar delocalization through the bridging unit.     

Light-induced degradation of the active layer of polymer-based solar cells

Polymer-based organic solar cells are known to offer a poor stability in real use conditions, and the photodegradation of the active organic layer plays an important role in the reduced lifetime of the devices. This paper focuses on the photodegradation of two conjugated polymers used in organic solar cells, namely poly(2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene (MDMO-PPV) and poly(3-hexyylthiophene) (P3HT), and their blends with [60]PCBM (methano-fullerene[6,6]-phenyl C61-butyric acid methyl ester), a fullerene derivative. MDMO-PPV and P3HT thin films were submitted to photoageing (λ > 300 nm) in the presence and in the absence of oxygen. The mechanisms by which these polymers degrade were elucidated. P3HT, pristine and blended with PCBM, was shown to be much more stable under illumination than MDMO-PPV. The results showed that, if deposited on an inert substrate and well protected from oxygen with a convenient encapsulation, P3HT:PCBM based active layer should be intrinsically stable for several years in use conditions.     

New access to H-phosphonates via metal-catalyzed phosphorus-oxygen bond formation

A novel approach to H-phosphonates from hypophosphorous acid using a transfer hydrogenation process was developed. This method is atom-economical, environmentally friendly, catalytic, and efficient, leading easily to H-phosphonate monoesters or ammonium salt in moderate to good yields.     

Characterization of conformers and dimers of antithrombin by capillary electrophoresis-quadrupole-time-of-flight mass spectrometry

Antithrombin (AT) is a plasma glycoprotein which possesses anticoagulant and anti-inflammatory properties. AT exhibits various forms, among which are native, latent and heterodimeric ones. We studied the potential of capillary electrophoresis-mass spectrometry (CE-MS) using a sheath liquid interface, electrospray ionization (ESI), and a quadrupole-time-of-flight (Q-TOF) mass spectrometer to separate and quantify the different AT forms. For CE separation, a neutral polyvinyl alcohol (PVA) coated capillary was employed. The protein conformation was preserved by using a background electrolyte (BGE) at physiological pH. A sheath liquid of isopropanol-water 50:50 (v/v) with 14 mM ammonium acetate delivered at a flow rate of 120 μL h⁻¹ resulted in optimal signal intensities. Each AT form exhibited a specific mass spectrum, allowing unambiguous distinction. Several co-injection experiments proved that latent AT had a higher electrophoretic mobility (μ_ep) than native AT, and that these conformers could associate to form a heterodimer during the CE analysis. The developed CE-MS method enabled the detection and quantitation of latent and heterodimeric forms in a commercial AT preparation stored at room temperature for three weeks.     

Stereoselective stilbene epoxidation over supported gold-based catalysts

The gold reference catalyst Au/TiO(2) exhibits high activity in the stereoselective epoxidation of trans-stilbene in methylcyclohexane in the presence of 5 mol% TBHP, by taking part in a chain reaction involving the activation of molecular oxygen by a radical produced from methylcyclohexane.     

Synthesis, ionisation potentials and electron affinities of hexaazatrinaphthylene derivatives

Several hexaazatrinaphthylene derivatives and a tris(thieno)hexaazatriphenylene derivative have been synthesised by reaction of the appropriate diamines with hexaketocyclohexane. The crystal structure of 2,3,8,9,14,15-hexachloro-5,6,11,12,17,18-hexaazatrinaphthylene has been determined by X-ray diffraction; this reveals a molecular structure in good agreement with that predicted by density functional theory (DFT) calculations and pi-stacking with an average spacing between adjacent molecular planes of 3.18 A. Solid-state ionisation potentials have been measured by using UV photoelectron spectroscopy and fall in the range of 5.99 to 7.76 eV, whereas solid-state electron affinities, measured using inverse photoelectron spectroscopy, vary in the range -2.65 to -4.59 eV. The most easily reduced example is a tris(thieno)hexaazatriphenylene substituted with bis(trifluoromethyl)phenyl groups; DFT calculations suggest that the highly exothermic electron affinity is due both to the replacement of the outermost phenylene rings of hexaazatrinaphthylene with thieno groups and to the presence of electron-withdrawing bis(trifluoromethyl)phenyl groups. The rather exothermic electron affinities, the potential for adopting pi-stacked structures and the low intramolecular reorganisation energies obtained by DFT calculations suggest that some of these molecules may be useful electron-transport materials.