Good Electron Acceptor Research Articles

Synthesis of a [60]fullerene‐functionalized poly(vinyl chloride) derivative by stereospecific chemical modification of PVC

AbstractThe covalent attachment of [60]fullerene (C60) to two poly(vinyl chloride) (PVC) samples with different isotactic content is achieved by direct reaction in o‐dichlorobenzene (o‐DCB) solution in the presence of AIBN. The extent of fullerenation is controlled by varying the C60 feed ratio. The pendant C60‐chemically modified PVC polymers are soluble in tetrahydrofuran (THF) and have been characterized by UV–vis, NMR, FTIR, DSC, TGA, cyclic voltammetry, and SEM. The quantitative microstructural analysis after covalent attachment of the bulky C60 moiety to the PVC has been followed by 13C NMR spectroscopy. From the results it can be concluded that the modification of PVC by graft reaction through free radical reaction proceeds by a stereoselective mechanism. This conclusion has been confirmed on the basis of the increase of the glass‐transition temperature (Tg) and the thermal stability of the C60‐chemical modified PVC samples. The fullerenated PVCs obtained show good electron acceptor properties, as evidenced by electrochemical investigations. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5408–5419, 2007

Photochemical Grafting of n-Alkenes onto Carbon Surfaces: the Role of Photoelectron Ejection

The grafting of molecular layers to carbon-based materials provides a way to combine the high chemical and thermal stability of these materials with surface properties such as chemical recognition or reactivity. The functionalization of surfaces with ultraviolet light has emerged as a way to modify difficult-to-functionalize materials, such as diamond. We have performed a combined experimental and computational investigation of the photochemical reaction of terminal alkenes with hydrogen-terminated carbon surfaces. 1-Alkenes carrying various terminal functional groups (-NHCOCF3, -NHCOO(tert-butyl), -COOCH3, -CH3) were grafted from the neat liquids using 254 nm light. These layers were characterized using X-ray Photoelectron Spectroscopy and Infrared Reflectance Absorption Spectroscopy. Pronounced differences in reactivity were observed between the molecules: trifluoroacetamide-terminated alkenes grafted the fastest and yielded self-terminating layers after approximately 4 h. Ultraviolet photoelectron spectroscopy and photocurrent measurements show that the grafting reaction involves photoemission of electrons into the liquid. Density functional calculations show that the reactivities of the four molecules are correlated with their electron affinities, with the trifluoroacetamide group acting as the best electron acceptor and having the highest reactivity. Our results demonstrate that photoejection of electrons from the solid into the acceptor levels of the alkenes initiates the functionalization reaction and controls the overall rate. Finally, marginally reactive n-alkenes were induced to react and form dense monolayers by seeding the carbon surface with small amounts of a good electron acceptor, such as the trifluoroacetamide moiety. This study provides important new mechanistic insights into the use of ultraviolet light to initiate grafting of alkenes onto surfaces.

CHARGE TRANSPORT THROUGH CARBON NANOTUBE OR FULLERENE–MOLECULE–SILICON JUNCTIONS

We report here the current–voltage (i–V) characteristics of several (n++- Si /MNOPE/ C 60/ Pt -tip) or (n++- Si /MNOPE/SWCNT/ Pt -tip) junctions, where MNOPE = 2'-mononitro-4, 4'-bis(phenylethynyl)-1-phenylenediazonium and SWCNT = single wall carbon nanotube. A layer of C 60 or SWCNT-derivatized MNOPE has strong effect on the i–V behavior of the junctions, including rectification, negative differential resistance (NDR) and switching behaviors. The i–V curve of a grafted molecular monolayer (GMM) of MNOPE atop n++- Si shows NDR behavior, whereas those of C 60- and SWCNT-derivatized GMMs of MNOPE on n++- Si show strong rectifying behavior with opposite rectification polarities. With C 60, larger currents were found with negative tip bias, while with SWCNT, the forward top bias was positive. Because C 60 tends to be a good electron acceptor and SWCNTs tend to be good electron donors, they show different i–V behavior, as observed. Some of the (n++- Si /MNOPE/SWCNT/ Pt -tip) junctions also show reversible bistable switching behavior.

Styryl dyes as new photoinitiators for free radical polymerization

Several disperse and cationic styryl dyes have been synthesized and evaluated for the initiation of free radical polymerization of ethyl acrylate under UV–vis light. The kinetic study of photoinitiated polymerization performed with the use of suitable electron donors such as ethyl 4- N, N-dimethylaminobenzoate (DMB), phenylthioacetic acid (PhSAc) and phenoxyacetic acid (PhOAc) has proved that tested dyes are good electron acceptors. It has been shown that the intermolecular electron transfer is the limiting step in the photoinitiated polymerization process.

Positive role of nitrite as electron acceptor on anoxic denitrifying phosphorus removal process

Literatures revealed that the electron acceptor-nitrite could be inhibitory or toxic in the denitrifying phosphorus removal process. Batch test experiments were used to investigate the inhibitory effect during the anoxic condition. The inoculated activated sludge was taken from a continuous double-sludge denitrifying phosphorus and nitrogen removal system. Nitrite was added at the anoxic stage. One time injection and sequencing batch injection were carried on in the denitrifying dephosphorus procedure. The results indicated that the nitrite concentration higher than 30 mg/L would inhibit the anoxic phosphate uptake severely, and the threshold inhibitory concentration was dependent on the characteristics of the activated sludge and the operating conditions; instead, lower than the inhibitory concentration would not be detrimental to anoxic phosphorus uptake, and it could act as good electron acceptor for the anoxic phosphate accumulated. Positive effects performed during the denitrifying biological dephosphorus all the time. The utility of nitrite as good electron acceptor would provide a new feasible way in the denitrifying phosphorus process.

Fluorescence Quenching Study on Electron Transfer from Certain Amines to Excited State Triphenylpyrylium Ion (TPP+)

The fluorescence quenching of excited singlet state of 2,4,6-triphenylpyrylium tetrafluoroborate (TPPBF4 or TPP+), a very good electron acceptor by amines were investigated in a acetonitrile solution using steady state technique. The bimolecular quenching rate constants lie in the range 2.11–10.26 × 1010 M-1 s-1. The driving force (ΔGet) for electron transfer process was calculated from the oxidation potential of amines and the reduction potential of TPP+. The observed k q values correlated well with the driving force for the electron transfer reactions. Aromatic amines show higher k q than aliphatic amines. From the oxidation potential of amines and the quenching rate constant values, a mechanism involving photoinduced electron transfer from amines to excited state TPP is suggested.

Search for More Stable C58X18 Isomers: Stabilities and Electronic Properties of Seven-Membered Ring C58X18 Fullerene Derivatives (X = H, F, and Cl)

Stimulated by recent preparation and characterization of the first C58F18 fullerene derivative, with a heptagon in the framework (Science, 2005, 309, 278), we have performed systematic density functional studies on the stabilities and electronic properties of two different structures C58X18 (A) and C58X18 (B), where X = H, F, and Cl. The large energy gaps between the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals (between 2.64 and 3.45 eV) and the aromatic character (with nucleus independent chemical shifts from -10.0 to -13.9 ppm) of C58X18 (A) and C58X18 (B) indicate that they possess high stabilities. Further investigations show that the heats of formation of C58X18 fullerene derivatives are highly exothermic, suggesting that adding nine X2's releases much of the strain of pure C58 fullerene and leads to stabilities of the derivatives. Lower in energy and stronger in aromatic character than C58F18 (B), which has been experimentally characterized, C58F18 (A) should also be isolated. In addition, C58F18 and C58Cl18 are predicted to possess large electron affinities, especially for C58F18 (B) and C58Cl18 (B) with values of 3.00 and 3.06 eV, respectively, even larger than that (2.50 eV) of C60F18. Hence, C58F18 and C58Cl18 can serve as good electron-acceptors with possible photonic/photovoltaic application. The IR spectra of C58X18 are simulated to facilitate identification of different isomers experimentally. In addition, the electronic spectra and second-order hyperpolarizabilities of C58X18 are predicted by ZINDO and sum-over-states model. With the addition of 9X2, both the static and frequency-dependent second-order hyperopolarizabilities of C58X18 greatly decrease compared to those of C58.

60]Fullerene‐Based Electron Acceptors

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

The interaction of benzene with Cu + sites in zeolites : IR studies and DFT quantum chemical calculations

As Cu + ions in zeolites catalyse several reactions of organic molecules, we undertook IR and DFT studies of the interaction of organic molecules with Cu +. Our previous studies had shown that Cu + was able to activate strongly the double and triple bonds in alkenes and acetylene, and less strongly the C O bond in acetone, which resulted in a distinct multiple bond weakening. The DFT calculations provided evidence that this was realized by π back donation of d electrons of Cu + to π * antibonding orbitals of the molecules. The present study concerns the activation of the benzene molecule, which is different from previously studied ones. It is a good electron acceptor, but the LUMO orbital of benzene has only a small antibonding character, therefore the interaction with Cu + was expected to result in a strong adsorption but only slight activation of the C–C bond. Our IR studies have shown, that the C–C bond weakening was indeed very small (Δ ν C–C = 13 cm −1, a value 10 times less than that for alkenes). DFT calculations showed that the molecule acquired a negative charge (−0.06) indicating that π back-donation prevailed over π donation. Both IR and DFT revealed that benzene adsorption on Cu + ions was relatively strong, which resulted in a withdrawing Cu + from the oxygen ring. DFT provided information on the geometry of the Cu +–benzene adduct and evidenced that the interaction of the benzene molecule with Cu + resulted in non-symmetric adsorption. The distances Cu +–C were in the range: 0.203–0.303 nm. The shorter the Cu +–C distance, the more important the bond activation. The benzene molecule interacting with Cu + was no longer flat, some hydrogens were directed towards Cu + and others in the opposite direction.

Oxidative addition to main group versus transition metals: Insights from the Activation Strain model

We have studied the oxidative addition of the methane C–H and chloromethane C–Cl bonds to a number of main group (Be, Mg and Ca) and transition metals (Pd, Zn and Cd), using relativistic density functional theory (DFT) at ZORA-BLYP/TZ2P. The purpose is to better understand what causes the characteristic differences in reactivity between main group and transition metals towards oxidative addition. Thus, we have analyzed our model reactions using the Activation Strain model in which the activation energy Δ E ≠ is decomposed into the activation strain Δ E strain ≠ of and the stabilizing TS interaction Δ E int ≠ between the reactants in the activated complex: Δ E ≠ = Δ E strain ≠ + Δ E int ≠ . Activation of the C–H bond goes with higher barriers than activation of the C–Cl bond because the higher bond strength of the former translates into a higher activation strain Δ E strain ≠ . The barriers for bond activation increase along Pd < Be, Ca < Mg < Zn, Cd. This can be straightforwardly understood through the TS-interaction Δ E int ≠ , that is, in terms of the bonding capabilities of the metals. Pd yields the lowest barriers because it achieves the most stabilizing Δ E int ≠ . This is the result of the small HOMO–LUMO gap between its occupied 4d and unfilled 5s AOs, which makes Pd both a good electron donor and acceptor. Zn and Cd yield the highest barriers because the large HOMO–LUMO gap between the occupied valence ns and unfilled valence np AOs makes them both poor donors and poor acceptors of electronic charge.

60]Fullerene-based electron acceptors

Abstract Although C 60 is a good electron acceptor molecule, most of its derivatives show decreased electronegativity in comparison to parent C 60 . The chemical modification of fullerenes has allowed us to enhance the electron acceptor ability of substituted fullerenes, thus making it feasible to modulate their electronic properties. Some of the most significant examples of the different strategies followed in this sense are highlighted in this review. To cite this article: B.M. Illescas, N. Martin, C. R. Chimie 9 (2006) .

EPR and DFT studies of the one-electron reduction product of phospholium cations

Cyclic voltammetry and EPR spectroscopy show that cationic phospholium groups are good electron acceptors whose reduction leads to a neutral radical where the unpaired electron is mainly delocalized on the carbon atoms of the five-membered ring. DFT calculations together with the crystal structure of phospholiums indicate that the electron addition causes a drastic diminution of the exocyclic CPC angle. The SOMO of reduced phospholium is compared to the SOMO of the phosphole radical anion.

Metal Oxide Thin Films Deposited from Metal Organic Precursors in Supercritical CO2 Solutions

This work demonstrates a novel method for deposition of metal oxide thin films, including Al2O3, ZrO2, MnOx, and RuOx where the metal−organic precursors and oxidizing agents are delivered in liquid and supercritical CO2. A cyclic deposition process is presented where reactants are introduced sequentially to control surface adsorption and byproduct removal steps. Reactions are studied in a hot wall reactor at pressures ranging from 1600 to 3600 psi at 80−200 °C, and X-ray photoelectron spectroscopy and infrared transmission confirmed metal oxide formation. We show that hydrogen peroxide is a viable O source for oxide deposition, whereas tert-butyl peracetate, which is a good electron acceptor, is less suited for oxygen donation. Capacitance versus voltage analysis of resulting Al2O3 films show good dielectric properties after post-deposition anneal. We believe that the good solvation properties of supercritical CO2 can aid in the delivery of precursors and in the removal of byproducts for advanced low-temp...

Unexpected Photophysical Properties of Symmetric Indolylmaleimide Derivatives

Arcyriarubin A and arcyriaflavin A, two strongly emissive and intensely colored natural products containing both two indoles and a maleimide unit, are investigated (in the flavin the two indole moieties are coupled by a cyclization). The photophysical properties of these compounds were studied in several solvents using UV-vis absorption, steady-state and time-resolved emission, nano- and femtosecond transient absorption spectroscopy. Furthermore, the effect of complexation with zinc(II) 1,4,7,11-tetraazacyclododecane on the photophysical properties of these natural products has been investigated. The chemical structures of the compounds would suggest a charge transfer (CT) character in the ground and/or excited states, since indole is a well-known electron donor and maleimide is a good electron acceptor. Their solvatochromic behavior was investigated by using the Kamlet-Taft approach and indicates only a small CT character in the excited state. This is substantiated by the time-resolved spectroscopy and the complexation study. Molecular orbital calculations indicate that there are no electronic transitions in which a large electron density is transferred from one indole unit to the maleimide part. All calculated orbitals show a strong delocalization of the electron density over the whole molecule. These findings corroborate the experimental results. Whereas the two compounds do have a substantial (calculated) ground-state dipole moment (6 D) and show some solvatochromic behavior, they behave more like conjugated aromatic systems than like electron donor-acceptor systems.

Multicomponent Donor−Acceptor Relay System Assembled within the Cavities of Zeolite Y. Photoinduced Electron Transfer between Ru(bpy)32+ and 2,4,6-Triphenylpyrylium in the Presence of Interposed TiO2

Zeolite Y containing Ru(bpy)32+ and TP+ has been obtained by the stepwise ship-in-a-bottle synthesis of the two components. The identity of the two ions has been demonstrated by diffuse reflectance UV−vis and IR spectra. Emission spectra (λex = 466 nm, λem = 600 nm) corresponding to the Ru(bpy)32+ lumophore indicate that 70% of the Ru(bpy)32+ complexes interact with TP+ through static quenching; only a weak emission corresponding to the unquenched complex is observed. The transient absorption spectrum of [Ru(bpy)32+−TP+]@Y obtained by laser flash photolysis is complex, but the presence of Ru(bpy)33+ was detected. The co-incorporation of semiconductor oxide TiO2 disfavors the Ru(bpy)32+−TP+ interaction, restoring the Ru(bpy)32+ emission to 90% of the original value. This indicates that small TiO2 clusters of a few Ti atoms occupying the empty zeolite space (1.3 nm) and, having a much larger band gap than regular TiO2, (∼50 nm) act mainly as insulators between good electron donor and acceptor molecules as opposed to electron relays.

Photophysical properties of fullerene-dendron-pyropheophorbide supramolecules

Abstract Two novel monofullerene-bis(pyropheophorbide a ) complexes were synthesized and their photophysical properties were studied by using both steady-state and time-resolved techniques. It was revealed that in the pyropheophorbide a (pyroPheo)-C 60 molecular system (FP1) strong quenching of the first excited singlet state of the pyroPheo and, as result, dramatically decreasing of photosensitized singlet oxygen generation occurs by efficient photoinduced electron transfer to the fullerene molecule with a rate constant of 2.5 × 10 9 s −1 . In contrast, the fullerene hexaadduct-bis(pyroPheo) system (FHP1), which possesses five diethyl malonate addends in the remaining octahedral positions, shows a high singlet oxygen quantum yield which is due to the reduced fullerene chromophore which is not a good electron acceptor anymore.

Three-way-output response system by electric potential: UV–vis, CD, and fluorescence spectral changes upon electrolysis of the chiral ester of tetracyanoanthraquinodimethane

The newly prepared tetracyanoanthraquinodimethane (TCNAQ) derivatives 1a, b with a chiral auxiliary are good electron acceptors and exhibit weak circular dichroism (CD) based on the absorption of TCNAQ. The twin-type electron acceptor 1c with two TCNAQ units shows larger ellipticity by exciton coupling. UV–vis, CD, and fluorescence spectra were changed drastically upon electrochemical reduction of 1c , which demonstrates the unprecedented three-way-output response system.

Kinetics of the Reactions of Water, Hydroxide Ion and Sulfide Species with CO2, OCS and CS2: Frontier Molecular Orbital Considerations

The kinetics of the reactions of water, hydroxide ion and sulfide species with CO2, OCS and CS2 are investigated using the molecular orbital approach and available kinetic data. Although these reactions are symmetry allowed, the lowest unoccupied molecular orbital (LUMO) for CO2 is a poor electron accepting orbital as it has a positive potential energy. At low pH, hydration of CO2 requires that the waters interact with CO2 via hydrogen bonding for subsequent formation of H2CO3 in an effort to overcome the high energy of activation. These factors are significant for the slow kinetics of hydration and the persistence of CO2 in water. The reaction of hydroxide ion with CO2 has a much smaller energy of activation. For the isoelectronic species OCS and CS2, their LUMO orbitals are good electron acceptor orbitals, and the energy of activation is less than that for the corresponding CO2 reactions. The LUMO orbitals for OCS and CS2 have less carbon character whereas the LUMO for CO2 has more carbon character. The relative rates of these reactions (CO2 > OCS > CS2) reflect the increased carbon character of the π* LUMO orbital for CO2 over CS2 and the fact that the LUMO for OCS is σ*, which when filled can readily break the C—S bond leading to sulfide (even though the C character of the LUMO is less than those for CO2 and CS2). Also, the higher hydrogen bonding interactions with nearest water molecules is in the order CO2 > OCS > CS2 indicating that hydrolysis via water catalysis is retarded as the number of S atoms increases. Solid phase FeS has a highest occupied molecular orbital (HOMO) with a potential energy similar to that of CO2 and can activate (or bond with) the carbon atom in CO2 so that organic compounds can be produced under hydrothermal vent conditions.

Quenching processes of aromatic hydrocarbons in the higher triplet excited states-energy transfer vs. electron transferElectronic supplementary information (ESI) available: The quenching of DBA(Tn) by CCl4, CHR(Tn) by NAP, the evidences of no DBA and CHR ions produced during two-color two-laser flash photolysis, and the evidence of formation of benzene/Cl complex. See http://www.rsc.org/suppdata/cp/b4/b400128a/

Quenching processes of several aromatic hydrocarbons (AH) such as naphthalene (NAP), dibenz[a,h]anthracene (DBA), and chrysene (CHR) in the higher triplet excited states (T2) by different quenchers (Q) such as p-dichlorobenzene, o-dicyanobenzene aromatic compounds, and chloroalkanes (RCl), have been investigated by the two-color two-laser excitation method. AH in the higher triplet excited states (AH(Tn, n ≥ 2)) initially generated by the excitation of AH(T1) at the wavelength tuned to the absorption of AH(T1). AH(Tn) decays to a AH(T2) with the longest lifetime among AH(Tn) through the fast internal conversion. In the presence of Q, the competition of triplet energy transfer (TENT) and electron transfer (ELT) reactions between AH(T2) and Q are expected. However, no AH radical cation was observed, especially when the quenchers were chloroalkanes such as carbon tetrachloride (CCl4), methylene dichloride (CH2Cl2), 1,2-dichloroethane, which are good electron acceptors. It is suggested that the TENT is important during the quenching of AH(Tn) by Q. The lifetimes of NAP(T2), DBA(T2), and CHR(T2) were calculated from the TENT quenching experiments. It was found that the lifetimes of AH(T2) increase in the order of NAP(T2) (4.5 ps) < DBA(T2) (16 ps) < CHR(T2) (60 ps), which is consistent very well with the energy gap law for the transition from AH(T2) to AH(T1).

Active species of horseradish peroxidase (HRP) and cytochrome P450: two electronic chameleons.

The active site of HRP Compound I (Cpd I) is modeled using hybrid density functional theory (UB3LYP). The effects of neighboring amino acids and of environmental polarity are included. The low-lying states have porphyrin radical cationic species (Por(*)(+)). However, since the Por(*)(+) species is a very good electron acceptor, other species, which can be either the ligand or side chain amino acid residues, may participate in electron donation to the Por(*)(+) moiety, thereby making Cpd I behave like a chemical chameleon. Thus, this behavior that was noted before for Cpd I of P450 is apparently much more wide ranging than initially appreciated. Since chemical chameleonic behavior property was found to be expressed not only in the properties of Cpd I itself, but also in its reactivity, the roots of this phenomenon are generalized. A comparative discussion of Cpd I species follows for the enzymes HRP, CcP, APX, CAT (catalase), and P450.