Photochemical studies on η5-cyclopentadienyl(triphenylphosphine)nickelalkyl and -aryl compounds

Photo-induced degradation studies of a series of organonickel complexes of the type (η⁵-C₅H₅)(PPh₃)Ni(R) (R = CH₃, C₂H₅, C₆H₅ and C₆H₄CH₃-p) as well as certain deuterated analogs have been undertaken. Photolysis of the methyl compounds in benzene as well as benzene-d₆ gives methane as the major gaseous product, the photogenerated methyl group abstracting hydrogen from either the cyclopentadienyl ring, from the solvent, or from another methyl group. The photo-induced dealkylation of the ethyl compound gives both ethylene and ethane, and is explained by β-hydride elimination followed by subsequent reaction of the hydrido intermediate with additional ethyl compound. The photolysis of the phenyl and p-tolyl complexes in benzene solution leads to biaryl formation, both from the coupling of two coordinated aryl groups as well as interactions with the solvent. Triphenylphosphine is a product in all of these photo-decomposition studies.     

<Emphasis Type="Italic">Meldrum</Emphasis>’s acid in heterocyclic synthesis: azoles incorporating a 2,4-dichlorophenoxy moiety with anticipated molluscicidal activity

Synthesis of the title ring system is described using ethyl 4-(2,4-dichlorophenoxy)-3-oxobutanoate as starting material. The latter was prepared through acylating Meldrum’s acid with the phenoxy acid chloride derivative. Correspondence: Emad M. El-Telbani, Pesticides Department, National Research Centre, Dokki, 12622 Cairo, Egypt.     

Regioselective bond cleavage in the dissociative electron transfer to benzyl thiocyanates

The electrochemical reduction of benzyl thiocyanate and p-nitrobenzyl thiocyanate was investigated in acetonitrile at an inert electrode. These two compounds reveal a change in the reductive cleavage mechanism, and more interestingly, they show a clear-cut example of a regioselective bond dissociation. Both phenomena may be understood on the basis of the dissociative ET theory and its extension to the formation/dissociation reactions of radical ions. While the effect of the standard oxidation potential of the leaving group seems to be predominant in understanding the change in the ET mechanism by changing the driving force, the regioselective cleavage is dictated by changes in the intrinsic barrier related to the nature of the substituent on the aryl moiety.     

Sensitized hole injection of phosphorus porphyrin into NiO: toward new photovoltaic devices

This paper describes the preparation and the characterization of a photovoltaic cell based on the sensitization of a wide band gap p-type semiconductor (NiO) with a phosphorus porphyrin. A photophysical study with femtosecond transient absorption spectroscopy showed that light excitation of the phosphorus porphyrin chemisorbed on NiO particles induces a very rapid interfacial hole injection into the valence band of NiO, occurring mainly on the 2-20 ps time scale. This is followed by a recombination in which ca. 80% of the ground-state reactants are regenerated within 1 ns. A photoelectrochemical device, prepared with a nanocrystalline NiO electrode coated with the phosphorus porphyrin, yields a cathodic photocurrent indicating that electrons indeed flow from the NiO electrode toward the solution. The low incident-to-photocurrent efficiency (IPCE) can be rationalized by the rapid back recombination reaction between the reduced sensitizer and the injected hole which prevents an efficient regeneration of the sensitizer ground state from the iodide/triiodide redox mediator. To the best of our knowledge, this work represents the first example of a photovoltaic cell in which a mechanism of hole photoinjection has been characterized.     

Synthesis,Morphological Control,and Properties of Silver Nanoparticles in Potential Applications

Nanostructured materials, especially nanoparticles (NPs), of noble metal NPs such as silver (Ag) have been the focus of research in recent decades because of their distinct physical, chemical, and biological properties. These materials have attracted considerable attention because of their potential applications, such as catalysis, biosensing, drug delivery, and nanodevice fabrication. Previous studies on Ag NPs have clearly demonstrated that their electromagnetic, optical, and catalytic properties are strongly influenced by their shape, size, and size distribution, which can be varied by using different synthetic methods, reducing agents, and stabilizers. The valuable optical properties of Ag NPs have allowed for new approaches in sensing and imaging applications, offering a wide range of detection modes, such as colorimetric, scattering, and surface‐enhanced Raman scattering techniques, at extremely low detection limits. Here, an overview of the various chemical, physical, and biological properties of Ag NP fabrication approaches to obtain the various shapes and sizes is presented.     

Eye‐safe UV stand‐off Raman spectroscopy for the ranged detection of explosives in the field

Increasing worldwide terrorist attacks involving explosives presents a growing need for a rapid and ranged explosive detection method that can safely be deployed in the field. Stand‐off Raman spectroscopy shows great promise; however, the radiant exposures of lasers required for adequate signal generation are often much greater than what is safe for the eye or the skin, restricting use of the technique to unpopulated areas. Here, by determining the safe exposure levels for lasers typically used in Raman spectroscopy, optimal parameter values are identified, which produce the largest possible detection range using power densities that do not exceed the eye‐safe limit. It is shown that safe ultraviolet pulse energies can be more than three orders of magnitude greater than equivalent safe visible pulse energies. Coupling this to the 16‐fold increase in Raman signal obtained in the ultraviolet at 266 nm over that at 532 nm results in a 131 times larger detection range for the eye‐safe 266‐nm system over an equivalent eye‐safe 532‐nm laser system. For the Raman system described here, this translates to a maximum range of 42 m for detecting Teflon with a 266‐nm laser emitting a 100‐mm diameter beam of 23.5‐mJ nanosecond pulses. Copyright © 2015 John Wiley & Sons, Ltd.     

Comparing the Efficiencies of Stochastic Isothermal Molecular Dynamics Methods

Molecular dynamics typically incorporates a stochastic-dynamical device, a “thermostat,” in order to drive the system to the Gibbs (canonical) distribution at a prescribed temperature. When molecular dynamics is used to compute time-dependent properties, such as autocorrelation functions or diffusion constants, at a given temperature, there is a conflict between the need for the thermostat to perturb the time evolution of the system as little as possible and the need to establish equilibrium rapidly. In this article we define a quantity called the “efficiency” of a thermostat which relates the perturbation introduced by the thermostat to the rate of convergence of average kinetic energy to its equilibrium value. We show how to estimate this quantity analytically, carrying out the analysis for several thermostats, including the Nosé-Hoover-Langevin thermostat due to Samoletov et al. (J. Stat. Phys. 128:1321–1336, 2007) and a generalization of the “stochastic velocity rescaling” method suggested by Bussi et al. (J. Chem. Phys. 126:014101, 2007). We find efficiency improvements (proportional to the number of degrees of freedom) for the new schemes compared to Langevin Dynamics. Numerical experiments are presented which precisely confirm our theoretical estimates.     

Synthesis and biological study of a new series of bifunctional organoiron thio‐ and seleno‐terephthalate derivatives (C5H5)Fe(CO)2ECO(C6H4)COX (E = S,X = R2N,RNH, NH2, OH,Cl; E = Se,X = RNH,RS, RCOO,NH2, OH,Cl)

A new series of bifunctional organoiron thio‐ and seleno‐terephthalate complexes — (η‐C₅H₅)Fe(CO)₂ECO(C₆H₄)COX [E = S; X = C₆H₁₁NH, (C₂H₅)₂N; and E = Se; X = P? CH₃? C₆H₄? NH, C₆H₅? C₂N₂O? S, m? NO₂? C₆H₄? CH?CH? COO] — has been synthesized via the organic transformation reactions of the terephthaloyl chloride precursors η‐(C₅H₅)Fe(CO)₂ECO(C₆H₄)COCl with the desired nucleophiles. These new complexes were characterized by elemental analysis, IR and ¹H NMR spectra. The above complexes, in addition to some other selected analogues, were tested for their antifungal, antibacterial and mutagenic activity. Our results show that all the selenium‐containing compounds have antifungal activity on Candida albicans and antibacterial effects against Bacillus subtilis and Staphylococcus aureus. Four of the six selenium‐containing derivatives exhibited growth inhibitory effects against Pseudomonas aeruginosa and/or Escherichia coli. Sulfur‐containing derivatives elicited activity against C. albicans, and each one of them showed activity against at least one of the bacterial strains that have been used in this investigation. Two selenium‐ and two sulfur‐containing derivatives showed mutagenic activity against one or more than one strain of the Salmonella typhimurium using the Ames test. Copyright © 2001 John Wiley & Sons, Ltd.     

Geometrical control of the interatomic coulombic decay process in quantum dots for infrared photodetectors

In electron dynamics calculations the interatomic Coulombic decay (ICD) process has recently been shown to take place in two vertically‐aligned quantum dots (QDs). Energy emitted during the relaxation of one electron in one QD is converted into kinetic energy of another electron ejected from a neighboring QD. As the electronic structure of QDs can be controlled by their geometries, we prove here in thorough scans of the transversal and vertical QD confinement potentials’ widths that geometries are likewise control parameters for ICD. Such a comprehensive investigation has been enabled by a significant development of the calculations in terms of speed achieved among others by optimization of the grid and Coulomb interaction operator representations. As key result of this study we propose two cigar‐shaped singly‐charged GaAs QDs vertically aligned in the direction of their long side for a most efficient QD ICD realization useful for an infrared photodetector. © 2016 Wiley Periodicals, Inc.