Supramolecular control over donor-acceptor photoinduced charge separation

A novel donor-bridge-acceptor system has been synthesized by covalently linking a p-phenylene vinylene oligomer (OPV) and a perylene diimid (PERY) at opposite ends of a m-phenylene ethynylene oligomer (FOLD) of twelve phenyl rings, containing nonpolar (S)-3,7-dimethyl-1-octanoxy side chains. For comparison, model compounds have been prepared in which either the donor or acceptor is absent. In chloroform, the oligomeric bridge is in a random coil conformation. Upon addition of an apolar solvent (heptane) the oligomeric bridge first folds into a helical stack and subsequently intermolecular self-assembly of the stacks into columnar architectures occurs. Photoexcitation in the random coil conformation, where the interaction between the donor and acceptor chromophores is small, results only in long-range intramolecular energy transfer in which the OPV singlet-excited state is transformed into the PERY singlet-excited state. In the folded conformation of the bridge, donor and acceptor are closer and their enhanced interaction favors the formation the OPV(*)(+)-FOLD-PERY(*)(-) charge-separated state upon photoexcitation. As a result, the extent of photoinduced charge separation depends on the degree of folding of the bridge between donor and acceptor and therefore on the apolar nature of the medium. As a consequence, and contrary to conventional photoinduced charge separation processes, the formation of the OPV(*)(+)-FOLD-PERY(*)(-) charge-separated state is more favored in apolar media.     

Building blocks for the molecular expression of quantum cellular automata. Isolation and characterization of a covalently bonded square array of two ferrocenium and two ferrocene complexes

The suitability of [{(eta5-C5H5)Fe(eta5-C5H4)}4(eta4-C4)Co(eta5-C5H5)][PF6]2, [1][PF6]2, for use as a molecular quantum cellular automata (QCA) cell is demonstrated. To this end the structure of 1 in the solid state and the conversion of 1 to mono- and dicationic mixed-valence complexes have been accomplished. The latter compounds have been isolated as pure materials and characterized by IR, EPR, and M?ssbauer spectroscopies and single-crystal XRD (monocation only) and magnetic susceptibility measurements. Near-IR spectra demonstrate the mixed valence character of the cations (valence trapped on the IR, EPR and M?ssbauer time scales), and the energies of the intervalence charge-transfer bands provide a measure of the hole hopping frequency.     

A study of the partitioning of the first-order reduced density matrix according to the theory of atoms in molecules

This work describes a simple spatial decomposition of the first-order reduced density matrix corresponding to an N-electron system into first-order density matrices, each of them associated to an atomic domain defined in the theory of atoms in molecules. A study of the representability of the density matrices arisen from this decomposition is reported and analyzed. An appropriate treatment of the eigenvectors of the matrices defined over atomic domains or over unions of these domains allows one to describe satisfactorily molecular properties and chemical bondings within a determined molecule and among its fragments. Numerical determinations, performed in selected molecules, confirm the reliability of our proposal.     

Diels-Alder Reactions of 2-Oxazolidinone Dienes in Polar Solvents Using Catalysis or Non-conventional Energy Sources

Summary. The (Z)-N-substituted 4-methylene-5-propylidene-2-oxazolidinone dienes were prepared by a one-step synthesis, starting from 2,3-hexanedione and isocyanates. Diels-Alder cycloadditions of these dienes were carried out in the presence of the dienophiles methyl vinyl ketone, methyl propiolate, and a captodative olefin, under conditions such as solvents of high polarity, Lewis acid catalysis, and non-conventional energy sources. The reactions carried out either with mixtures of H₂O/MeOH or under BF₃·Et₂O catalysis yielded the highest regio- and stereoselectivities. The use of ionic liquids, microwaves, and ultrasound did not significantly increase the selectivity.     

Electrochemical behavior of 1-nitroso-2-naphthol in aqueous solutions: Evaluation of the rate constant for the intervening chemical step in an ece mechanism from stirred-mercury-pool chronoamperometric data

In aqueous solution 1-nitroso-2-naphthol is reduced to 1-amino-2-naphthol by an ECE mechanism. The homogeneous first-order rate constant for the chemical reaction of the intermediate can be evaluated with the aid of current-time data obtained during controlled-potential electrolysis with a stirred mercury-pool working electrode, using the Karp-Meites equation for the dependence of quantity of electricity on time, and is found to be equal to 1.1 ± 0.1₅ s^?1.     

Solutions of fractional gas dynamics equation by a new technique

In this paper, a novel technique is formed to obtain the solution of a fractional gas dynamics equation. Some reproducing kernel Hilbert spaces are defined. Reproducing kernel functions of these spaces have been found. Some numerical examples are shown to confirm the efficiency of the reproducing kernel Hilbert space method. The accurate pulchritude of the paper is arisen in its strong implementation of Caputo fractional order time derivative on the classical equations with the success of the highly accurate solutions by the series solutions. Reproducing kernel Hilbert space method is actually capable of reducing the size of the numerical work. Numerical results for different particular cases of the equations are given in the numerical section.     

Three‐step synthesis of arylpolyboronic acids from phenols via organotin compounds

In this paper we describe a three‐step synthesis of aryldi‐ and triboronic acids starting from phenols. Several substituted phenols (I) were converted into the corresponding aryldiethylphosphates (II) in good to excellent yields. The latter, on reaction with sodium trimethylstannide in liquid ammonia, under irradiation, afforded the aryl‐ and heteroarylpoly(trimethylstannyl) derivatives in 65–90% yield. The third step is the reaction of the organotin compounds with borane in THF, which leads to the corresponding arylpolyboronic acids in around 80% yield. In order to confirm their structure, some of the diboronic acids were converted into the corresponding pinacol esters. The results obtained in a study on the synthesis of various terphenyls through double and triple Suzuki couplings catalyzed by palladium acetate between the obtained arylpolyboronic acids and various aryl halides are also reported. These reactions proceeded with an average 65% yield, and also enabled us to confirm the structures of some of the diboronic acids. The structure of the new compounds was determined by ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy, mass spectrometry and IR spectroscopy. Copyright © 2007 John Wiley & Sons, Ltd.