Exploring the synthesis and impact of end‐functional poly(3‐hexylthiophene)

In recent years, end‐functional poly(3‐hexylthiophene) (P3HT) has proven to be instrumental in the continued development and innovation within the broad conjugated polymer arena, enabling a variety of applications, particularly in organic electronics. The availability of P3HT with controlled molecular weights, low polydispersity, and importantly, a wide range of reactive end‐groups not only serves as a key building block for the preparation of conjugated block copolymers but also facilitates the development of hybrid nanocomposite materials via inorganic surface modification strategies. This Highlight focuses on the synthetic approaches to end‐functional P3HT and the impact of these systems in emerging technologies. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 831–841     

Effects of solvent flow,dopant flow,and lamp current on dopant-assisted atmospheric pressure photoionization (DA-APPI) for LC-MS. Ionizationvia proton transfer

In this paper, the effects of solvent flow, dopant flow, and lamp power on proton transfer ionization in dopant-assisted (DA) atmospheric pressure photoionization (APPI) are investigated. A broad theoretical framework is presented, describing the primary photoionization process, the formation of protonated-solvent cluster ions, and the balance between analyte ion creation via proton transfer and loss via recombination. The principal experimental test system utilized methanol as the solvent, toluene as the dopant, and acridine as the analyte. Comparisons are made between acridine and a less basic compound, 9-methylanthracene (9-MA). Experimental determinations of the trends in the analyte MH⁺ signal and the total ion current (TIC) with variations in the subject parameters are provided. Experimental results and theory demonstrate that both the analyte signal and the TIC approach asymptotic limits with increases in dopant flow and/or lamp current (two factors which dictate the rate of photoion generation). The data show that these limits are lowered at higher solvent flow rates. These results are attributed to the recombination loss process, the rate of which increases with the second power of ion concentration. We deduce that the recombination rate constant increases with solvent flow rate, a consequence of the growth of ion-solvent clusters. Cluster growth is also believed to be a factor in the dramatic loss of sensitivity for 9-MA that occurs as the solvent flow is raised, because larger protonated-solvent cluster ions have greater solvation energies and may be unreactive with compounds having low gas-phase basicity and/or low solvation energy.     

Magnetic and spectroscopic investigation of partially reduced vanadium pentoxides. II. β′-CuxV2O5

The magnetic, electron paramagentic resonance (EPR), infrared (ir), and optical properties of β′-Cu_xV₂O₅ have been measured and interpreted. Magentic susceptibility studies indicate that β′-Cu_xV₂O₅ undergoes a semiconductor → metal transition near x = 0.60. For x ? 0.40, the magnetic data interpreted in terms of a ligand-field model in which the octahedral ²T_2g term of V⁴⁺ is split by the combined perturbations of axial distortion and spin-oribt coupling, with the result that the ²T_2g term is split into a magnetic ground level, a weakly magentic intermediate level, and a magnetic highest level. The results of the magnetic analysis further support the transition to metallic behavior with increasing x. The EPR spectra are motionally narrowed by electronic hopping at low temperatures, and the g-tensor and linewidth data are in good agreement with the magnetic results. The ir spectra are independent of x and exhibit narrow bands at 1020 and 995 cm^?1, which are attributed to the stretching vibration of multiple VO bonds. The optical spectra consist of two main bands whose peak positions shift to higher frequencies with increasing x, implying that the V⁴⁺O bond distances decrease with increasing x. The results of this study are in excellent agreement with Goodenough's interpretation of β-M_xV₂O₅.     

Kinetics and mechanism of the reaction between N-and N,N′-methyl ethylenediamines and palladium(II) chloro complexes in aqueous acid medium

The substitution of N-alkyl substituted ethylenediamines for chloride ions in the rapidly equilibrating system has been investigated in aqueous acid medium. The kinetic data can be accommodated by the general rate law where n = 0, 1, or 2 and m = 0, 1, or 2, depending on whether none, one, or two methyl groups are attached to the two nitrogen atoms of ethylenediamine. Reaction with the most heavily substituted ethylenediamine, namely, N₂N₂en discloses a change of the mentioned rate law to on going from a lower to a higher chloride ion concentration range. This change in the mathematical form of the rate law can be explained in terms of an ion-pair association of N₂N₂enH⁺ and free chloride ions.     

Model of nanocrystal formation in solution by burst nucleation and diffusional growth

The phenomenon of burst nucleation in solution, in which a period of apparent chemical inactivity is followed by a sudden and explosive growth of nucleated particles from a solute species, has been given a widely accepted qualitative explanation by LaMer and co-workers. Here, we present a model with the assumptions of instantaneous re-thermalization below the critical nucleus size and irreversible diffusive growth above the critical size, which for the first time formulates LaMer's explanation of burst nucleation in a manner allowing quantitative calculations. The behavior of the model at large times, t, is derived with the result that the average cluster size, as measured by the number of atoms, grows approximately t, while the width of the cluster distribution grows approximately (sq root)1.We develop an effective numerical scheme to integrate the equations of the model and compare the asymptotic expressions to results from numerical simulation. Finally, we discuss the physical effects which cause real nucleation processes in solution to deviate from the behavior of the model.     

Automatic generation of active coordinates for quantum dynamics calculations: application to the dynamics of benzene photochemistry

A new practical method to generate a subspace of active coordinates for quantum dynamics calculations is presented. These reduced coordinates are obtained as the normal modes of an analytical quadratic representation of the energy difference between excited and ground states within the complete active space self-consistent field method. At the Franck-Condon point, the largest negative eigenvalues of this Hessian correspond to the photoactive modes: those that reduce the energy difference and lead to the conical intersection; eigenvalues close to 0 correspond to bath modes, while modes with large positive eigenvalues are photoinactive vibrations, which increase the energy difference. The efficacy of quantum dynamics run in the subspace of the photoactive modes is illustrated with the photochemistry of benzene, where theoretical simulations are designed to assist optimal control experiments.     

Heterogeneity versus duration dependence with competing risks: an application to the labor market

Two hypotheses can explain the declining probability of gaining employment as an unemployment spell wears on: heterogeneity of the unemployed versus duration dependence. The nonparametric tests developed in the literature for testing duration dependence would not account for the fact that an unemployment spell can terminate in other ways than employment. The nonparametric tests developed in this paper extend, under certain conditions, those tests to competing risks. We illustrate our test using US unemployment data in which we find little consistent evidence for duration dependence. © 2017 The Authors. Applied Stochastic Models in Business and Industry published by John Wiley & Sons, Ltd.     

Characterisation of InAs/GaAs short period superlattices using column ratio mapping in aberration-corrected scanning transmission electron microscopy

The image processing technique of column ratio mapping was applied to aberration-corrected high angle annular dark field (HAADF) images of short period MBE (molecular beam epitaxy) grown InAs/GaAs superlattices. This method allowed the Indium distribution to be mapped and a more detailed assessment of interfacial quality to be made. Frozen-phonon multislice simulations were also employed to provide a better understanding of the experimental column ratio values. It was established that ultra-thin InAs/GaAs layers can be grown sufficiently well by MBE. This is despite the fact that the Indium segregated over 3-4 monolayers. Furthermore, the effect of the growth temperature on the quality of the layers was also investigated. It was demonstrated that the higher growth temperature resulted in a better quality superlattice structure.     

Rapid coherent optical modulation of atomic momenta via pseudoresonances

We show that modulation of an optical field injected into a cavity containing a dilute Bose-Einstein condensate is transformed into a modulation of the population of the atomic momentum states due to pseudoresonances of the resolvent which describes the linearized evolution of the atom-cavity system. This effect is related to the way the atomic momentum states and the cavity optical field are dynamically coupled. The results presented offer new possibilities for rapid modulation of atomic momentum state populations up to 3 orders of magnitude faster than modulation of magnetic trapping potentials.