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81.
John J. Morelli Somayajula K. Viswanadham Andrew. G. Sharkey JR. David M. Hercules 《International journal of environmental analytical chemistry》2013,93(2-4):295-323
Abstract Laser mass spectra obtained for 20 organophosphorus (OP) compounds were systematically evaluated for groups containing analogous structural features. Variations in fragmentation can be understood based on simple organic reactions. While detailed mechanistic interpretations of the laser mass spectra (LMS) were not possible, the qualitative features in the LMS obtained from five compounds, not in the original set, could be predicted based on the characteristics of the other OP compounds studied. The success of the prediction lends credence to the qualitative models developed for rationalizing the LMS. A specific feature in the LMS of aromatic thionophosphates is a thiono-thiolo rearrangement. Detailed investigation into the phenomena involved comparison of LMS obtained from aromatic thionophosphates with spectra from electron impact, chemical ionization, field desorption, and secondary ion mass spectrometry. These results led to the conclusion that the rearrangement in laser mass spectrometry must occur during volatilization while the molecule/ion is in the “cloud” present immediately above the laser impact area. 相似文献
82.
Several low molecular weight alkanes have been polymerized (polycondensed) over HSO3 F-SbF5 to yield a highly branched oily oligomer with a molecular weight range from the molecular weight of the monomer to around 700. The order of reactivity for butane and lower molecular alkanes is isobutane > n-butane > propane > ethane > methane. The reactivity is explained by the ease of attack of an acid proton derived from the acid on the alkane sigma bonds as well as the relative stability of the resulting cation formed. A cationic mechanism for this reaction is proposed. 相似文献
83.
84.
S. A. Liebman D. H. Ahlstrom W. H. Starnes JR. F. C. Schilling 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(6):935-950
This study compares the use of pyrolysis hydrogenation gas chromatography (PHGC) and 13C Fourier transform nuclear magnetic resonance (FTNMR) methods for the analysis of reference polyethylene (PE) samples, ethylene-α-olefin copolymers, and specially prepared poly(vinyl chloride) (PVC) samples which were reduced to their PE skeletal structures. The nature and relative quantities of the short branches along the polymer chains were determined using both techniques. Improved high-resolution PHGC data, obtained with a fused silica capillary separation column, gave results which were in satisfactory agreement with the 13C FTNMR data. This approach confirms that detailed microstructural information can be obtained with these methods by using carefully controlled experimental conditions and appropriate reference systems. 相似文献
85.
The tentative identification of the reactive species in the condensation of Cp2 TiCl2 with salts of diacids to form titanium polysters is made. The reactive species are believed to be the same for both aqueous solution and interfacial systems, i.e., R -CO2 ? and Cp2 Ti2+ with reaction occurring in the aqueous phase. The condensation of Cp2 TiCl2 with disodium terephthalate in interfacial systems occurs via a pseudo-first-order reaction: Rate = K[Cp2 TiCl2] The rate-determining step (s) is believed to be diffusion of CP2 TiCl2 into the aqueous layer and/or hydrolysis of Cp2 TiCl2 相似文献
86.
Bronstein H Chen Z Ashraf RS Zhang W Du J Durrant JR Tuladhar PS Song K Watkins SE Geerts Y Wienk MM Janssen RA Anthopoulos T Sirringhaus H Heeney M McCulloch I 《Journal of the American Chemical Society》2011,133(10):3272-3275
We report the synthesis and polymerization of a novel thieno[3,2-b]thiophene-diketopyrrolopyrrole-based monomer. Copolymerization with thiophene afforded a polymer with a maximum hole mobility of 1.95 cm(2) V(-1) s(-1), which is the highest mobility from a polymer-based OFET reported to date. Bulk-heterojunction solar cells comprising this polymer and PC(71)BM gave a power conversion efficiency of 5.4%. 相似文献
87.
OVERSTREET GEORGE A. JR; BREDLEY EDWIN L. JR 《IMA Journal of Management Mathematics》1996,7(4):291-311
Although credit-scoring models represent a widely used managerialaid for large financial intermediaries, the vast majority ofU.S. credit unionsrelatively small cooperatively ownedretail intermediaries, constrained by sample and funding limitationshaveyet to adopt such techniques. Lovie & Lovie (1986) havetheorized that the flat-maximum effect or curve of insensitivityassociated with linear scoring models could be advantageousin areas of applied prediction such as credit scoring. In thiscontext, we reported the relative predictive power of genericcredit-scoring models versus customized models in an earlierpaper (Overstreet et al. 1992). Unfortunately, these findingswere not readily adaptable to the credit-union industry dueto a dated sample with incomplete credit-bureau information.Consequently, from 1988 to 1991, we gathered a refined databasefrom which to further develop and field-test generic scoringmodels in the credit-union environment. The results reportedherein not only confirm, but amplify, the relative predictivepower of such models found earlier. Relative costs and benefitsof generic versus customized models are modelled for a representativecredit union. Future research directions are set forth in theconclusions. 相似文献
88.
Ohkita H Cook S Astuti Y Duffy W Tierney S Zhang W Heeney M McCulloch I Nelson J Bradley DD Durrant JR 《Journal of the American Chemical Society》2008,130(10):3030-3042
We report herein a comparison of the photophysics of a series of polythiophenes with ionization potentials ranging from 4.8 to 5.6 eV as pristine films and when blended with 5 wt % 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]C61 (PCBM). Three polymers are observed to give amorphous films, attributed to a nonplanar geometry of their backbone while the other five polymers, including poly(3-hexylthiophene), give more crystalline films. Optical excitation of the pristine films of the amorphous polymers is observed by transient absorption spectroscopy to give rise to polymer triplet formation. For the more crystalline pristine polymers, no triplet formation is observed, but rather a short-lived (approximately 100 ns), broad photoinduced absorption feature assigned to polymer polarons. For all polymers, the addition of 5 wt % PCBM resulted in 70-90% quenching of polymer photoluminescence (PL), indicative of efficient quenching of polythiophene excitons. Remarkably, despite this efficient exciton quenching, the yield of dissociated polymer+ and PCBM- polarons, assayed by the appearance of a long-lived, power-law decay phase assigned to bimolecular recombination of these polarons, was observed to vary by over 2 orders of magnitude depending upon the polymer employed. In addition to this power-law decay phase, the blend films exhibited short-lived decays assigned, for the amorphous polymers, to neutral triplet states generated by geminate recombination of bound radical pairs and, for the more crystalline polymers, to the direct observation of the geminate recombination of these bound radical pairs to ground. These observations are discussed in terms of a two-step kinetic model for charge generation in polythiophene/PCBM blend films analogous to that reported to explain the observation of exciplex-like emission in poly(p-phenylenevinylene)-based blend films. Remarkably, we find an excellent correlation between the free energy difference for charge separation (deltaG(CS)rel) and yield of the long-lived charge generation, with efficient charge generation requiring a much larger deltaG(CS)rel than that required to achieve efficient PL quenching. We suggest that this observation is consistent with a model where the excess thermal energy of the initially formed polaron pairs is necessary to overcome their Coulombic binding energy. This observation has important implications for synthetic strategies to optimize organic solar cell performance, as it implies that, at least devices based on polythiophene/PCBM blend films, a large deltaG(CS)rel (or LUMO level offset) is required to achieve efficient charge dissociation. 相似文献
89.
We show for the first time that the photogenerated hole lifetime in TiO 2 is a strong determinant of the ability of TiO 2 to split water. Hole lifetimes were measured using transient absorption spectroscopy over a range of excitation intensities. The lifetimes of the holes were modulated by the use of exogenous scavengers and were also found to vary systematically with the excitation intensity. In all cases the quantum yield of oxygen production is found to be linked to the light intensity used, ranging from below 1 sun equivalent to nearly 1 sun equivalent. We also provide evidence that oxygen production requires four photons for each molecule of oxygen, which is reminiscent of the natural photosynthetic water-splitting mechanism. This in turn suggests a mechanism for oxygen production which requires four-hole chemistry, presumably via three, as yet unidentified intermediates. It is also shown that at excitation densities on the order of 1 sun, nongeminate electron-hole recombination limits the quantum yield significantly. 相似文献
90.
Shoaee S Eng MP An Z Zhang X Barlow S Marder SR Durrant JR 《Chemical communications (Cambridge, England)》2008,(40):4915-4917
We report on photoinduced charge separation in solid films of two perylene diimides; intramolecular charge separation and recombination is correlated with a reduction in the yield of long-lived, intermolecular charge-separated species. 相似文献