Non-aromatic Solvents Research Articles

Photoluminescence characteristics of a highly soluble fullerene-containing polymer

We investigated the photoluminescence (PL)|characteristics of a highly soluble, fullerene-containing copolymer in both solution and film states. In solution state, the copolymer showed different PL characteristics depending on the aromaticity of the solvent. The PL from polystyrene segments of the copolymer was strongly quenched in an aromatic solvent, while the PL from fullerene remained unchanged. However, the films cast from an aromatic and a nonaromatic solvent demonstrated very similar PL characteristics, implying that the chain alignment or orientation and packing in the films occur in a similar way irrespective of the solvent.

Synthesis, characterization, and reactivity of half-sandwich Ru(II) complexes containing phosphine, arsine, stibine, and bismutine ligands

The synthesis and some reactions of the Ru(II) and Ru(IV) half-sandwich complexes [RuCp(EPh 3)(CH 3CN) 2] + (E=P, As, Sb, Bi) and [RuCp(EPh 3)(η 3-C 3H 5)Br] + have been investigated. The chemistry of this class of compounds is characterized by a competitive coordination of EPh 3 either via a RuE or a η 6-arene bond, where the latter is favored when the former is weaker, that is in going down the series. Thus in the case of Bi, the starting material [RuCp(CH 3CN) 3] + does not react with BiPh 3 to give [RuCp(BiPh 3)(CH 3CN) 2] + but instead gives only the η 6-arene species [RuCp(η 6-PhBiPh 2)] + and [(RuCp) 2(μ-η 6,η 6-Ph 2BiPh)] 2+. Similarly, the EPh 3 ligand can be replaced by an aromatic solvent or an arene substrate. Thus, the catalytic performance of [RuCp(EPh 3)(CH 3CN) 2] + for the isomerization of allyl-phenyl ethers to the corresponding 1-propenyl ethers is best with E=P, while the conversion drops significantly using the As and Sb derivatives. By the same token, only [RuCp(PPh 3)(CH 3CN) 2] + is stable in a non-aromatic solvent, whereas both [RuCp(AsPh 3)(CH 3CN) 2] + and [RuCp(SbPh 3)(CH 3CN) 2] + rearrange upon warming to [RuCp(η 6-PhEPh 2)] + and related compounds. In addition, the potential of [RuCp(EPh 3)(CH 3CN) 2] + as precatalysts for the transfer hydrogenation of acetophenone and cyclohexanone has been investigated. Again aromatic substrates are clearly less suited than non-aromatic ones due to facile η 6-arene coordination leading to catalyst's deactivation.

Effect of Solvents on the Selectivity of Free-Radical Chlorination of Functionalized Ethanes, Propanes, and Tetrachloroethene

Free radical reactions of hydrogen abstraction from methane, ethane, propane, and isobutane by radicals X (X = Cl·, Br·, I·, and CH· 3) are used as an example to study the applicability of the molecular mechanics (MM) method and the modified intermediate neglect of differential overlap method (PM3) to describing the trends in activation energies. The activation energies of only some, but not all, reaction series are adequately described by the MM (if special parameterization is used) and PM3 methods. All of the four reaction series follow the same correlation within the framework of the parabolic model of a transition state. The correlation of activation energies with the energies of highest occupied molecular orbitals (HOMO) of substrates and solvents is explained. For the correct description of trends in the HOMO energies in the series of studied molecules, the PM3 method was parameterized. The MM and PM3 methods are used to reveal the effect of a solvent on the activation energies of the regioselective and substrate-selective free-radical chlorination of substituted ethanes and propanes. The calculations of the structure and strength of complexes formed by solvent molecules, chloroethane, its radical, and the chlorine radical made it possible to propose a mechanism for the solvent effect on regioselectivity. This mechanism consists in the stabilization of the transition state formed by the α-abstraction of a carbon atom from the C–Cl bond in the aromatic solvent. Different trends exist for aromatic and nonaromatic solvents for changes in the activation energies of the competitive chlorination of tetrachloroethene and 1,2-dichloroethane depending on the solvent concentration. These trends can be reduced to one trend if one considers the HOMO energies of solvents and the substrate and takes into account reactant concentrations.

Solvation-Induced Morphology Effects on the Performance of Polymer-Based Photovoltaic Devices

Polymer-based photovoltaic devices have been fabricated by blending the conjugated polymer, poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) with the buckminsterfullerene, C60. The photo-induced current and the open-circuit voltage show a strong dependence on the polymer processing conditions. It was found that the photovoltaic devices fabricated with tetrahydrofuran or chloroform (non-aromatic solvents) have smaller photocurrents under same reverse bias as well as higher open circuit voltages than the devices fabricated with xylene, dichlorobenzene, or chlorobenzene (aromatic solvents). The device performance dependence on the processing solvent is attributed to the different solvation-induced polymer morphology.

Poly(phenylacetylene) with bulky chiral germyl groups: synthesis and effects of measuring solvents and temperature on chiroptical properties

(+)- p-[{Methyl(1-naphthyl)phenyl}germyl]phenylacetylene, an acetylene with a bulky chiral germyl group, was polymerized with [(nbd)RhCl] 2–Et 3N to give a high-molecular-weight polymer in good yield. The CD spectrum of the polymer exhibited very large molar ellipticities [ θ] in the UV region in non-aromatic solvents (e.g. THF and CHCl 3). In contrast, the CD signals of the polymer in aromatic solvents (e.g. toluene, tetralin, and benzene) became appreciably smaller: [ θ] max=6.4×10 4 (330 nm) and −4.7×10 4° cm 2 dmol −1 (370 nm) in CHCl 3; [ θ] max=1.1×10 4 (330 nm) and −0.7×10 4° cm 2 dmol −1 (370 nm) in toluene. The [ θ] max values of the polymer in aromatic solvents increased when the solutions were heated, which is attributed to decreased π–π interaction between the solvents and side groups.

Solvent effects on the thioamide rotational barrier: an experimental and theoretical study.

The solvent effect on the C-N rotational barriers of N,N-dimethylthioformamide (DMTF) and N,N-dimethylthioacetamide (DMTA) has been investigated using ab initio theory and NMR spectroscopy. Selective inversion recovery NMR experiments were used to measure rotational barriers in a series of solvents. These data are compared to ab initio results at the G2(MP2) theoretical level. The latter are corrected for large amplitude vibrational motions to give differences in free energy. The calculated gas phase barriers are in very good agreement with the experimental values. Solvation effects were calculated using reaction field theory. This approach has been found to give barriers that are in good agreement with experiment for many aprotic, nonaromatic solvents that do not engage in specific interactions with the solute molecules. The calculated solution-phase barriers for the thioamides using the above solvents are also in good agreement with the observed barriers. The solvent effect on the thioamide rotational barrier is larger than that for the amides because the thioamides have a larger ground-state dipole moment, and there is a larger change in dipole moment with increasing solvent polarity. The transition-state dipole moments for the amides and thioamides are relatively similar. The origin of the C-N rotational barrier and its relation to the concept of amide "resonance" is examined.

Device performance and polymer morphology in polymer light emitting diodes: The control of device electrical properties and metal/polymer contact

We recently demonstrated that the morphology of a spin-cast polymer film can be controlled by the proper choice of solvent, polymer solution concentration, and spin speed [Y. Shi, J. Liu, and Y. Yang, J. Appl. Phys. 87, 4254 (2000)]. In this article, we report the correlation between the morphology and the electrical properties of poly(2-methoxy-5-(2’-ethyl-hexyloxy)-1,4-phenylene vinylene based light emitting diodes. The performance of these devices, such as device turn-on voltage, current injection efficiency, and quantum efficiency, shows a strong dependence on thin film processing conditions. It is found that aromatic solvents and nonaromatic solvents have very different effects on device performance, which suggests that the solvation induced morphology effect is one of the controlling factors for polymer-based optoelectronic devices.

Proper Tuning of Comprehensive Two-Dimensional Gas Chromatography (GC×GC) to Optimize the Separation of Complex Oil Fractions

Comprehensive two-dimensional gas chromatography (GC×GC) is an utterly suitable separation technique for the analysis of complex samples, such as oil fractions. Once the two columns and the operating conditions are properly tuned, the technique is able to provide a detailed characterization of such materials. Some considerations applying to the tuning of a GC×GC system for a specific separation are presented and discussed. The authors present a number of different column sets and conditions which allow the separation of a non-aromatic hydrocarbon solvent, a kerosene, the light end of a crude oil, and an olefinic fraction, respectively. The highly structured GC×GC chromatograms, together with chemical knowledge about the samples, provide a much more comprehensive characterization of the samples than hitherto possible.

Proper Tuning of Comprehensive Two-Dimensional Gas Chromatography (GC×GC) to Optimize the Separation of Complex Oil Fractions

Comprehensive two-dimensional gas chromatography (GC×GC) is an utterly suitable separation technique for the analysis of complex samples, such as oil fractions. Once the two columns and the operating conditions are properly tuned, the technique is able to provide a detailed characterization of such materials. Some considerations applying to the tuning of a GC×GC system for a specific separation are presented and discussed. The authors present a number of different column sets and conditions which allow the separation of a non-aromatic hydrocarbon solvent, a kerosene, the light end of a crude oil, and an olefinic fraction, respectively. The highly structured GC×GC chromatograms, together with chemical knowledge about the samples, provide a much more comprehensive characterization of the samples than hitherto possible.

Interaction of Ground and Excited (S1) States of C60 and C70 with Aromatic Amines: Exciplex and Charge-Transfer Emissions

Emissions from both exciplexes and excited charge-transfer (CT) complexes have been observed for the fullerene−aromatic amine systems in nonaromatic solvents and solvent mixtures using steady-state fluorescence measurements. Support for the exciplex and CT emissions has also been obtained from the time-resolved fluorescence measurements. Both emissions are very sensitive to the polarity of the solvents. From the solvatochromic shifts of the emission maxima, dipole moments (μ) of the exciplexes and the excited CT complexes have been estimated. For C60−N,N-dimethylaniline (DMAN) and C60−N,N-diethylaniline (DEAN) systems, the μ values for the exciplexes and the excited CT complexes are in the ranges 10−12 and 25−27 D, respectively. Both species are thus very polar in nature. In aromatic solvents the fullerene−aromatic amine systems behave differently, without forming any exciplexes, though the fullerene emissions are quenched by the amines with almost diffusion-controlled rates. CT emissions are also not observed in the aromatic solvents. The π-electrons of the solvent molecules are supposed to be responsible for the unusual behavior of these solvents on the present systems.

Solvent Effects on the Barrier to C−N Bond Rotation in N,N-Dimethylaminoacrylonitrile: Modeling by Reaction Field Theory and by Monte Carlo Simulations

Solvents are known experimentally to influence strongly the barrier to rotation about the conjugated C−N bond of N,N-dimethylaminoacrylonitrile (DMAAN). The barrier increases with overall solvent polarity, but solvent hydrogen-bond donor ability does not have a measurable effect. Two solvation models were explored in an attempt to reproduce the experimental data and obtain insight into the causes of the observed solvent effects. Calculations based on the isodensity polarizable continuum model (IPCM) encoded in Gaussian 94, a representative dielectric continuum-based procedure, yielded fair agreement for aprotic, nonhalogenated, nonaromatic solvents. The model predicts a linear correlation with the Onsager dielectric function, (e − 1)/(2e + 1), which was observed experimentally for this set of solvents. However, the model underestimated the magnitude of the solvent dependence by approximately 30%. As a representative example of an approach based on the use of explicit solvent molecules, Monte Carlo simulat...

Simple and condensed β-lactams, part 31. Acid catalyzed ring closures and ring transformations of some 3-aryloxy-4-oxoazetidine-2-carbaldehydes

Carbaldehydes 1a and 1b, when treated with Lewis or Brønsted acids in non-aromatic solvents or in nitrobenzene afford dihydrochromeno[3,2- b]azet-2(1 H)-ones of types 4–6 and 10. In toluene, chloro- and fluoro-benzene related compounds of types 7–9 were obtained, in the last named two solvents accompanied by pyrrolidin-2-one derivatives 11–15.

Rotational Isomers in Stacked Macrocycles: Synthesis and Spectroscopic Properties of Peripherally Substituted (μ-Oxo)bis(phthalocyaninatosilicon) Compounds

The synthesis and spectroscopic properties of a series of soluble octaalkoxy-substituted silicon phthalocyanine monomers, (RO)8PcSi(OSiMe2tBu)L, and μ-oxo-bridged dimers, [(RO)8PcSi(OSiMe2tBu)]2O (R = H17C8-, H25C12-, (±)-3,7-Me2-C8H15-, (±)-2-Et-C6H12-; L = -OSiMe2tBu, -OSiMe3, -F, -OH), are reported. The optical absorption spectra of all dimers show strong solvatochromic behavior whereas the monomers do not. In nonaromatic solvents like, e.g., dichloromethane, the Q-band of the dimers is split into at least five broad bands between 560 and 760 nm, and proton NMR spectra show a strong splitting (Δδ = 1 ppm) of the aromatic signal at low temperature, indicating a torsion angle of ∼20−30° between the rings. In aromatic solvents such as, e.g., benzene, toluene, or 1-methylnaphthalene, thermochromism of the dimers is observed. This is shown by temperature-dependent optical absorption spectroscopy to be due to the presence of a second isomer exclusively found in solutions of aromatic solvents. It shows a rath...

Remarkable Effects of Metal, Solvent, and Oxidant on Metalloporphyrin-Catalyzed Enantioselective Epoxidation of Olefins

Three metal complexes of one particular homochiral porphyrin were investigated as catalysts for enantioselective epoxidation of unfunctionalized olefins under various reaction conditions. Much better results were obtained with the iron and ruthenium complexes than with the manganese derivative. The absence of any effect of amines on the iron porphyrin-catalyzed reaction in benzene, as well as the superior results in aromatic as opposed to both more and less polar nonaromatic solvents, suggest that specific association of aromatic molecules to the metalloporphyrin affects its solution structure. Strong evidence for the involvement of active oxidants that are more selective than trans-dioxoruthenium(VI) porphyrin is provided by the significant effect of primary oxidants on the ruthenium porphyrin-catalyzed reactions. Preliminary results with the iron complex of an only slightly modified porphyrin under the optimized reaction conditions found in this study resulted in epoxidation of styrene and 4-chlorostyre...

Effect of Aromatic Solvents Dissolved in an Aqueous Phase on Ion-pair Solid-phase Extraction

The effect of aromatic solvents dissolved in an aqueous phase at the 10–3 mol dm–3 level on the distribution of an ion pair between octadecylsilane (ODS)-modified silica gel and cellulose nitrate was studied systematically. Bis[2-(5- chloro-2-pyridylazo)-5-diethylaminophenolato]cobalt(III) ion and dodecanesulfonate ion were the cation (C+) and anion (A–) studied. The extent of distribution was expressed in terms of the ion-pair extraction constant, Kex, which is defined as Kex = [C+·A–]s/[C+][A–], where the subscript s denotes the solid phase and no subscript the aqueous phase. In the ODS–silica gel system, nitrobenzene (NB), p-methylnitrobenzene (p-MNB), p-ethylnitrobenzene (p-ENB) and o-, m- and p-xylene enhanced the Kex value by more than two orders of magnitude. Other aromatic solvents such as toluene, chlorobenzene and benzene also enhanced Kex. Non-aromatic solvents, such as chloroform, dichloromethane and octan-2-ol had no effect on the extraction. The solvent effect cannot be described in terms of a model of ion-pair solvent extraction. The effect was interpreted through mutual interactions of key constituents of the solid phase, organic solvent and ion pair. The key structual fragments present in an effective solvent are a phenyl group and nitro and alkyl groups on the phenyl group. In the proposed model, the alkyl group on the phenyl group interacts with the octadecyl group on the ODS–silica gel through a hydrophobic force, and the negatively polarized nitro group and/or π electrons in the benzene ring of the solvent adsorbed on the ODS interact with the ion pair through electrostatic forces. In the cellulose nitrate system, the solvent effects were small even in the case of NB, p-MNB and p-ENB. The effect must be saturated by the nitro group originally present in the matrix of cellulose nitrate.

Photochemical Behavior of 1,3-Diaryltriazene 1-Oxides

Abstract Photolysis of the 1,3-dipolar unsymmetrical 1,3-triazene 1-oxides in aromatic and nonaromatic solvents led to their decomposition. 2-Hydroxyazobenzene, mono- and disubstituted biaryls were produced.

Microscopic solvation and femtochemistry of charge-transfer reactions: the problem of benzene(s)-iodine binary complexes and their solvent structures

Charge-transfer reactions are studied on the femtosecond and picosecond time scales and under controlled composition in a molecular beam. The system of interest is iodine in aromatic and non-aromatic solvents, which goes back to Hildebrand and Mulliken almost 50 years ago. For the first time, the isolated binary complex and its solvated structural dynamics are studied. The product iodine atoms are positively identified and the concept of harpoon mechanism introduced. The dynamics are related to the impact geometry of the transition state and the electronic structure. A global potential energy surface is described with molecular dynamics detailing the motion in the reaction coordinates.

Initiation Step of Radical Polymerization of Styrene in Various Non-Aromatic Solvents

Rates of initiation of radical polymerizations (R i ) of styrene by several initiators in non-aromatic solvents were determined and compared with those in benzene. It is considered that by forming π-complex with a geminate radical, benzene suppresses cage recombination when both are bulky, but assists it when one is small. But non-aromatic solvents show only viscosity effect and are considered to be inert-solvents

Electronic absorption and emission spectroscopic investigations of the interaction of the fullerenes, C60 and C70, with amines and aromatic molecules

Electronic absorption spectroscopy and fluorescence spectroscopy have been used to investigate the interaction of the fullerenes C60 and C70 with diethylaniline, and with aromatic solvents such as benzene. C60 interacts weakly with aromatic amines in the ground state while C70 does not interact at all. Steady state fluorescence emission and lifetime measurements show that both C60 and C70 form excited state complexes (exciplexes) with the amines in non-aromatic solvents such as methylcyclohexane, but not in benzene. In benzene, only fluorescence quenching is observed due to the interaction between the π systems of the aromatic solvent and the fullerene in the ground state. This is also borne out by the systematic study of solvent effects on the absorption and emission spectra of the fullerenes.

Interaction of C 60 and C 70 with aromatic amines in the ground and excited states. Evindence for fullerene—benzene interaction in the ground state

While C 60 interacts with aromatic amines such as dimethylaniline in the ground state, C 70 does not. Fluorescence spectroscopic studies, including lifetime measurements, show the formation of exciplexes of both C 60 and C 70 with aromatic amines in nonaromatic solvents such as methylcyclohexane. Exciplexes are however not formed in benzene solvent, due to π—π interaction between benzene and the fullerene. Based on spectroscopic absorption measurements, it is shown that both C 60 and C 70 do indeed interact with benzene in the ground state.