Planarized star-shaped oligothiophenes with enhanced pi-electron delocalization

[structure: see text] Planarized star-shaped oligothiophenes 1 have been synthesized by connecting short-chain oligothiophenes on a benzo[1,2-b:3,4-b':5,6-b' ']trithiophene central core. Their electrochemical and optical properties have been characterized by cyclic voltammetry and UV-visible spectroscopy, respectively. These results associated with theoretical calculations show the advantage of benzotrithiophene as a central core in terms of pi-electron delocalization.     

Covalent adlayer growth on a diamond thin film surface

The surface of boron-doped diamond thin films can be modified by exposure to a strong oxidizing agent, resulting in the formation of -OH and =O terminated diamond. The -OH groups are reacted with an acid chloride to produce a covalently bound, modified diamond thin film surface. The demonstration of these reactions allows for the facile modification of diamond surfaces using techniques well established for oxide surfaces. Characterization of the covalently bound species shows submonolayer coverage, and time-resolved fluorescence measurements are reflective of the highly featured nature of the diamond film.     

Total synthesis of the formamicin aglycon,formamicinone

[structure: see text] The total synthesis of formamicinone (2), the aglycone of formamicin (1), has been accomplished via the late-stage Suzuki cross-coupling of fragments 5 and 6, the macrolactonization of seco ester 14, and the Mukaiyama aldol reaction of aldehyde 3 and methyl ketone 4. An efficient and highly stereoselective second generation synthesis of vinyl iodide 6 is also described.     

A multi-wall carbon nanotube–molecular semiconductor composite for bi-layer organic solar cells

A water-soluble composite of oxidised multi-wall carbon nanotubes and sulphonic acid sodium salt derivatised copper phthalocyanine for application in bi-layer organic solar cells is reported. Measurements of the topography of thin films of this novel material and of the valence electronic structure of its two components are used to rationalise the photovoltaic characteristics of a model organic heterojunction utilising the nanocomposite as the hole-extracting electrode and donor layer.     

Density functional theory on phase space

Forty‐five years after the point de départ [Hohenberg and Kohn, Phys Rev, 1964, 136, B864] of density functional theory, its applications in chemistry and the study of electronic structures keep steadily growing. However, the precise form of the energy functional in terms of the electron density still eludes us—and possibly will do so forever [Schuch and Verstraete, Nat Phys, 2009, 5, 732]. In what follows we examine a formulation in the same spirit with phase space variables. The validity of Hohenberg–Kohn–Levy‐type theorems on phase space is recalled. We study the representability problem for reduced Wigner functions, and proceed to analyze properties of the new functional. Along the way, new results on states in the phase space formalism of quantum mechanics are established. Natural Wigner orbital theory is developed in depth, with the final aim of constructing accurate correlation‐exchange functionals on phase space. A new proof of the overbinding property of the Müller functional is given. This exact theory supplies its home at long last to that illustrious ancestor, the Thomas–Fermi model. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Temperature dependence of X- and Q-band EPR spectra of the dinuclear manganese(II) complex [(NO2Bpmp)Mn2(mu-OAc)2]+: determination of the exchange constant and of the spin parameters for the S=1, 2, and 3 spin states

A new dinuclear manganese(II) complex was synthesised with the biscompartimental ligand 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-nitrophenol (NO(2)BpmpH) and characterised by X-ray crystallography. Magnetic susceptibility measurements revealed that the two high-spin Mn(II) ions are antiferromagnetically coupled with a singlet-to-triplet separation of 7.2 cm(-1). The powder EPR spectra were recorded for both X- and Q-bands between 1.8 K and 35 K. A detailed analysis of these spectra led to the determination of three out of five individual spin-state zero-field splitting parameters. From the proposed simulations, the exchange coupling constant J and the intermetallic distance have been computed.     

Small D–π–A Systems with o‐Phenylene‐Bridged Accepting Units as Active Materials for Organic Photovoltaics

Donor–acceptor (D–π–A) systems that combine triarylamine donor blocks and dicyanovinyl (DCV) acceptor groups have been synthesized. Starting from the triphenylamine (TPA)? thiophene? DCV compound ( 1 ) as a reference system, various synthetic approaches have been developed for controlling the light‐harvesting properties and energy levels of the frontier orbitals in this molecule. Thus, the introduction of methoxy groups onto TPA, the replacement of one phenyl ring of TPA by a thiophene ring, or the extension of the π‐conjugating spacer group lead to the modulation of the HOMO level. On the other hand, the fusion of the DCV group onto the vicinal thiophene ring by an ortho‐phenylene bridge allows for a specific fine‐tuning of the LUMO level. The electronic properties of the molecules were analyzed by using UV/Vis spectroscopy and cyclic voltammetry and the compounds were evaluated as donor materials in basic bilayer planar heterojunction solar cells by using C₆₀ as acceptor material. The relationships between the electronic properties of the donors and the performance of the corresponding photovoltaic devices are discussed. Bilayer planar heterojunction solar cells that used reference compound 1 and C₇₀ afforded power‐conversion efficiencies of up to 3.7 %.     

Correlation of mercury concentrations in tree core and lichen samples in southeastern Louisiana

To determine if a correlation exists between mercury concentrations in lichens and wood from tree cores, tree core and lichen samples were taken from sites under mercury advisories and analyzed for mercury using a Bacharach 50B Mercury Analyzer System employing the Manual Cold Vapor Atomic Absorption EPA method 7471A. Wood from tree cores was dated using tree ring data. Wood samples from the cores were analyzed for various depths in the tree core (periods of time) to determine if variations occur throughout the cores. Preliminary data indicate that a strong correlation exists between mercury concentrations in tree core and lichen samples. Samples were analyzed for the 6-month period of summer 2003–winter 2004. A correlation coefficient of 0.882 was found between the tree core and lichen data sets. The derived correlations were used to estimate concentrations of mercury in tree rings for sites in lichen samples which were previously analyzed. These predicted values compared favorably to recently determined concentrations of Hg in tree cores. The strong correlation between lichen and tree core Hg concentrations suggests similar uptake mechanism for the two types of biota.     

Development of a Xanthine Oxidase Modified Amperometric Electrode for the Determination of the Antioxidant Capacity

This paper describes the development of a xanthine oxidase/poly‐m‐phenylenediamine (XOD‐PPD)‐modified electrode. The biosensor was constructed by encapsulating XOD in a sol‐gel matrix deposited onto a platinum based screen‐printed electrode functionalized with a permselective PPD membrane. The hydrogen peroxide generated as a final product of the enzymatic reaction between the hypoxanthine and the XOD or by the spontaneous dismutation of superoxide radicals was selectively monitored at +700 mV. The use of a highly selective PPD layer blocked the nonspecific oxidation of other oxidizable molecules. Finally the biosensor was applied to the determination of the antioxidant capacity of acetylsalicylic acid.     

Electronic structure of lanthanum transition-metal oxyarsenides LaMAsO (M = Fe,Co, Ni) and LaFe1−xM′xAsO (M′ = Co,Ni) by X-ray photoelectron and absorption spectroscopy

The electronic structures of the quaternary oxyarsenides LaMAsO (M = Fe, Co, Ni) were examined with X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES). Interpretation of the metal 2p_3/2 and arsenic 3d_5/2 binding energies, as well as a satellite feature in the Co 2p XPS spectrum, suggests charges that are much less extreme than expected (i.e., not M²⁺ and As^3?) because of the strong covalent character within the M–As bonds. As M is varied, the differing degrees of charge transfer from M to As atoms within these bonds are manifested by shifts in the As 3d_5/2 binding energies and changes in the As K-edge intensities. This charge transfer is isolated within the [MAs] layer and does not influence the O 1s and La 3d XPS spectra. Fitting the experimental valence band spectra of these oxyarsenides LaMAsO yielded electron populations of states that support the formal charge assignment [La³⁺O^2?][M²⁺As^3?]. The mixed-metal series LaFe_1?xM′_xAsO (M′ = Co, Ni) was examined by XANES; analysis of the metal K- and L-edges, as well as of the Co 2p XPS satellite feature, revealed that no metal–metal charge transfer takes place.