Determination of oxygen,fluorine and boron by 14-MeV INAA: A case of multiple interferences

Oxygen and fluorine have been simultaneously determined by 14-MeV INAA in samples containing boron. Both boron and fluorine can cause serious interferences in the determination of oxygen. The fluorine and boron interference corrections for oxygen determination have been determined to be 0.43±0.01 and 0.0832±0.0017 apparent g oxygen per g of fluorine and boron, respectively, for our system. Boron can be determined in the same sample by a second irradiation. Mutual interferences have been evaluated and the procedure has been applied to NIST SRM and several other compounds.     

Role of polaron pair diffusion and surface losses in organic semiconductor devices

By applying Monte Carlo simulations we find that the extraction of bound polaron pairs (PP) at the electrodes is an important loss factor limiting the efficiency of organic optoelectronic and photovoltaic devices. Based upon this finding, we develop a unified analytic model consisting of exact Onsager theory describing the dissociation of PP in organic donor-acceptor heterojunctions, the Sokel-Hughes model for the extraction of free polarons at the electrodes, as well as of PP diffusion leading to the aforementioned loss mechanism, which was not considered previously. Our approach allows us to describe the simulation details on a macroscopic scale and to gain fundamental insights, which is important in view of developing an optimized photovoltaic device configuration.     

Is the nuclear spin-orbit interaction changing with neutron excess?

The difference in the energies of the lowest states corresponding to the two nodeless single-particle orbitals outside the Z=50 closed proton shell, h(11/2) and g(7/2), increases with neutron excess. We have measured the Sn(alpha,t) reaction for all seven stable even Sn isotopes and found that the spectroscopic factors are constant for these two states, confirming their characterization as single-particle states. The trend in energies is consistent with a decrease in the nuclear spin-orbit interaction. A similar trend, also suggesting a decreasing spin-orbit splitting, is seen in the energies of the neutron single-particle states outside the N=82 core, i(13/2) and h(9/2).     

Influence of charge carrier mobility on the performance of organic solar cells

The power conversion efficiency of organic solar cells based on donor–acceptor blends is governed by an interplay of polaron pair dissociation and bimolecular polaron recombination. Both processes are strongly dependent on the charge carrier mobility, the dissociation increasing with faster charge transport, with raised recombination losses at the same time. Using a macroscopic effective medium simulation, we calculate the optimum charge carrier mobility for the highest power conversion efficiency, for the first time accounting for injection barriers and a reduced Langevin‐type recombination. An enhancement of the charge carrier mobility from 10^–8 m²/V s for state of the art polymer–fullerene solar cells to about 10^–6 m²/V s, which yields the maximum efficiency, corresponds to an improvement of only about 20% for the given parameter set. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Urocanic acid photobiology. Photochemical binding of urocanic acid to bovine serum albumin

Abstract— The photolysis of E-[ring-2-¹⁴C]urocanic acid with bovine serum albumin (BSA) leads to incorporation of radiolabel into the protein. Levels up to 68 nmol mg^?1 BSA have been observed if the irradiation is carried out in an inert atmosphere. Oxygen reduces the level slightly. It appears from gel-filtration chromatography that the label incorporation is covalent in nature.     

Charge carrier mobilities in organic semiconductor crystals based on the spectral overlap

The prediction of substance‐related charge‐transport properties is important for the tayloring of new materials for organic devices, such as organic solar cells. Assuming a hopping process, the Marcus theory is frequently used to model charge transport. Here another approach, which is already widely used for exciton transport, is adapted to charge transport. It is based on the spectral overlap of the vibrational donor and acceptor spectra. As the Marcus theory it is derived from Fermi's Golden rule, however, it contains less approximations, as the molecular vibrations are treated quantum mechanically. In contrast, the Marcus theory reduces all vibrational degrees of freedom to one and treats its influence classically. The approach is tested on different acenes and predicts most of the experimentally available hole mobilities in these materials within a factor of 2. This represents a significant improvement to values obtained from Marcus theory which is qualitatively correct but frequently overestimates the mobilities by factors up to 10. Furthermore, the charge‐transport properties of two derivatives of perylene bisimide are investigated. © 2016 Wiley Periodicals, Inc.     

Finite element error bounds for a curve shrinking with prescribed normal contact to a fixed boundary

We approximate the evolution of a curve subject to motion bycurvature by linear finite elements. The curve evolves insidea given domain and meets orthogonally. We derive optimal boundsfor the error with respect to the L²- and H¹-norms and presentsome computed examples.     

Experimental and Theoretical Investigations of the Existence of CuII,CuIII, and CuIV in Copper Corrolato Complexes

The most common oxidation states of copper in stable complexes are +I and +II. Cu^III complexes are often considered as intermediates in biological and homogeneous catalysis. More recently, Cu^IV species have been postulated as possible intermediates in oxidation catalysis. Despite the importance of these higher oxidation states of copper, spectroscopic data for these oxidation states remain scarce, with such information on Cu^IV complexes being non‐existent. We herein present the synthesis and characterization of three copper corrolato complexes. A combination of electrochemistry, UV/Vis/NIR/EPR spectroelectrochemistry, XANES measurements, and DFT calculations points to existence of three distinct redox states in these molecules for which the oxidation states +II, +III, and +IV can be invoked for the copper centers. The present results thus represent the first spectroscopic and theoretical investigation of a Cu^IV species, and describe a redox series where Cu^II, Cu^III, and Cu^IV are discussed within the same molecular platform.