Showing papers on "Acetonitrile published in 2000"

Aqua, Alcohol, and Acetonitrile Adducts of Tris(perfluorophenyl)borane: Evaluation of Brønsted Acidity and Ligand Lability with Experimental and Computational Methods

Abstract: Equilibrium studies have been performed to determine the Bronsted acidity of [(C6F5)3B(OH2)]·H2O, the aqua species that exists in acetonitrile solutions of B(C6F5)3 in the presence of water NMR spectroscopic analysis of the deprotonation of [(C6F5)3B(OH2)]·H2O with 2,6-But2C5H3N in acetonitrile allows a pK value of 86 to be determined for the equilibrium [(C6F5)3B(OH2)]·H2O ⇄ [(C6F5)3B(OH)]- + [H3O]+ On the basis of a calculated value for the hydrogen bond interaction in [(C6F5)3B(OH2)]·H2O, the pKa for (C6F5)3B(OH2) is estimated to be 84 in acetonitrile Such a value indicates that (C6F5)3B(OH2) must be regarded as a strong acid, with a strength comparable to that of HCl in acetonitrile Dynamic NMR spectroscopic studies indicate that the aqua and acetonitrile ligands in (C6F5)3B(OH2) and (C6F5)3B(NCMe) are labile, with dissociation of H2O being substantially more facile than that of MeCN, by a factor of ca 200 in rate constant at 300 K Ab initio calculations were performed in the gas phase and wit

A Macrobicyclic Receptor with Versatile Recognition Properties: Simultaneous Binding of an Ion Pair and Selective Complexation of Dimethylsulfoxide

Abstract: A bicyclic receptor was synthesized and evaluated for its ability to bind alkali halide salts and polar neutral molecules in organic solvents. The receptor design is relatively straightforward in the sense that it is a combination of a dibenzo-18-crown-6 and a bridging 1,3-phenyldicarboxamide. In the presence of 1 mol equiv of metal cation, chloride affinities are enhanced in the order: K+ (9-fold enhancement) > Na+ (8-fold enhancement) ≫ Cs+ (no enhancement). An X-ray crystal structure shows that the receptor binds sodium chloride as a solvent-shared ion pair. The receptor has very weak affinity for acetonitrile, nitromethane, or acetone in chloroform solvent, whereas the association constant for dimethylsulfoxide is 160 M-1 at 295 K. An X-ray crystal structure shows that the dimethylsulfoxide is bound deeply in the receptor cavity and forms hydrogens bonds to the receptor via a bridging water molecule. There is also evidence for CH−O interactions. Solid−liquid extraction studies show that the receptor ...

Interaction of Urea with a Hydroxide-Bridged Dinuclear Nickel Center: An Alternative Model for the Mechanism of Urease

Abstract: A hydroxide-bridged dinuclear nickel complex with a urea molecule linking the two metal ions through its carbonyl oxygen atom has been prepared as a model for the metalloenzyme urease. This complex, [Ni2(μ-OH)(μ-urea)(bdptz)(urea)(CH3CN)](ClO4)3, where bdptz is the dinucleating ligand 1,4-bis(2,2‘-dipyridylmethyl)phthalazine, effects the hydrolysis of urea upon heating in a two-step reaction. In the first step, a molecule of ammonia is eliminated from urea with concomitant production of cyanate, the first-order rate constant in acetonitrile being (7.7 ± 0.5) × 10-4 h-1. This reaction is at least 500 times faster than the spontaneous decomposition of urea under the same conditions. When the cyanate-containing product is further heated in the presence of water, the cyanate is hydrolyzed with a second-order rate constant of (9.5 ± 1) × 10-4 M-1 h-1. Reaction of [Ni2(μ-OH)(μ-urea)(bdptz)(urea)(CH3CN)](ClO4)3 in 50% aqueous acetonitrile afforded ammonia with no appreciable buildup of the cyanate-containing spe...

Iron(II) Triflate Salts as Convenient Substitutes for Perchlorate Salts: Crystal Structures of [Fe(H2O)6](CF3SO3)2 and Fe(MeCN)4(CF3SO3)2

Abstract: The most convenient source of anhydrous iron(II) triflate is the acetonitrile solvate isolated from the reaction of finely divided iron metal with triflic acid in acetonitrile. The cyrstalline Fe(MeCN)4(OTf)2 readily loses two MeCN molecules under vacuum to afford Fe(OTf)2·2MeCN, which is stable to air oxidation but absorbs water. Crystals of the hexahydrate containing a hydrogen-bonded, layered structure are obtained from water.

A dimeric titanium-containing polyoxometalate. Synthesis, characterization, and catalysis of H2O2-based thioether oxidation.

Abstract: The previously unknown titanium(IV)-containing μ-hydroxo dimeric heteropolytungstate (Bu4N)7[(PTiW11O39)2OH] (TBA salt of H1) has been synthesized, starting from H5PTiW11O40, and characterized by elemental analysis, multinuclear (31P, 17O, 183W) NMR, IR, FAB-MS, cyclic voltammetry, and potentiometric titration. 31P NMR reveals that H1 (δ −12.76) readily forms in MeCN from the Keggin monomer (POM), PTiW11O405- (2, δ −13.34), upon the addition of 1.5 equiv of H+, via the protonated species, P(TiOH)W11O394- (H2, δ −13.44). The ratio of H1, 2, and H2, which are present in equilibrium in MeCN solution at 25 °C, depends on the concentration of both H+ and H2O. The Ti−O−Ti linkage readily reacts with nucleophilic reagents, such as H2O and ROH, to yield monomeric Keggin derivatives. μ-Hydroxo dimer H1 shows higher catalytic activity than 2 for thioether oxidation by hydrogen peroxide in acetonitrile. The reaction proceeds readily at room temperature and affords the corresponding sulfoxide and sulfone in ca. quant...

Adaptive self-assembly: environment-induced formation and reversible switching of polynuclear metallocyclophanes.

Abstract: Ligand 3 has been shown to self-assemble under coordination of copper(II) cations in a 1:1 ratio in acetonitrile to give equilibrating mixtures of a [2 x 2] grid-type tetranuclear structure 1 and a hexanuclear achitecture of hexagonal shape 2. The latter was confirmed by determination of the crystal structure which further indicated that 2 contained acetonitrile molecules and hydroxo groups bound to the copper(II) centers, which are therefore five-coordinate. The structures assigned to 1 and 2 were further supported by the spectral (mass, UV/Vis) data. The self-assembly process is strongly dependent on the conditions of the medium. An increase in concentration in acetronitrile increases the relative amount of hexamer 2, which appears to be the favored entity at the highest concentrations that can be reached before precipitation occurs. On the other hand, in nitromethane only the tetranuclear complex 1 was detected by mass spectrometry. Replacement of nitromethane by acetonitrile and vice versa indicated the reversible switching between a solution containing either 1 alone or an equilibrium mixture of 1 and 2, respectively. In conclusion, the system described presents several remarkable features: 1) self-assembly with substrate binding, 2) dynamic combinatorial structure generation, and 3) environment-induced structural switching amounting in effect to a process of adaptive self-assembly.

Platinum(IV)-Assisted [2 + 3] Cycloaddition of Nitrones to Coordinated Organonitriles. Synthesis of Δ4-1,2,4-Oxadiazolines

Abstract: [2 + 3] cycloaddition between acetonitrile ligands in the platinum(IV) complex [PtCl4(MeCN)2] and the nitrones -O+N(R3)C(R1)(R2) [R1 = H, R2 = Ph, o-C6H4OH, p-C6H4Me, p-C6H4OMe, p-C6H4NO2, p-C6H4NM...

Conductive F-doped Tin Dioxide Sol−Gel Materials from Fluorinated β-Diketonate Tin(IV) Complexes. Characterization and Thermolytic Behavior

Abstract: Hydrolysis and condensation of (CH3COCHCOCH3)2SnF(Otert-Am) and (CF3COCHCOCH3)2Sn(Otert-Am)2 gave soluble stannic oxo-oligomers or -polymers including fluorine and β-diketonate groups. Under thermal treatment in air at 550 °C, they yielded nanocrystalline fluorine-doped tin dioxide powders. The amount of remaining ligands in the xerosols depends on the hydrolysis ratio and on the nature of the solvent used, dimethylformamide (DMF) favoring ligand removal. The thermolytic reactions have been investigated by thermogravimetry coupled to mass spectrometry: (1) the β-diketonate ligands pyrolyze in two stages, at 200 and 320 °C, involving two different processes; (2) elimination of polar solvents of high boiling point, such as DMF, occurs up to 300 °C; (3) fluorine is lost as fluorhydric acid from 230 °C. The best strategy to prepare F-doped SnO2 materials by the sol−gel route is thus to start from precursors including Sn−F bonds and to use a polar aprotic solvent of low boiling point such as acetonitrile. It l...

Substituted 1,5-Diphenyl-3-benzothiazol-2-yl-Δ2-pyrazolines: Synthesis, X-ray Structure, Photophysics, and Cation Complexation Properties

Abstract: The spectroscopic properties of 1-phenyl-3-benzothiazol-2-yl-5-(4-R-phenyl)-Δ2-pyrazolines are strongly dependent on both the electronic nature of the substituent R and solvent polarity. As revealed by spectroscopic studies as a function of solvent polarity as well as temperature, for electron-rich amino donor substituents in polar solvents, deactivation of the strongly emissive charge transfer (CT) state of the basic 1-phenyl-3-benzothiazol-2-yl-Δ2-pyrazoline chromophore has to compete with a fast intramolecular electron transfer (ET) quenching reaction. In the case of the dimethylamino derivative (R = DMA), the rate constant of ET in acetonitrile was determined to ket = 3 × 1010 s-1. This ET process can be utilized for metal ion sensing by introducing nitrogen containing aza crown ether receptor units to the 4-position of the 5-phenyl group. The spectroscopically determined ET rates of the 5-(N-alkyl)anilino substituents, a DMA, a tetrathia- (AT415C5), and a tetraoxa-monoaza-15-crown-5 (A15C5) group, co...

Cytochrome c Structure and Redox Function in Mixed Solvents Are Determined by the Dielectric Constant

Abstract: Cyclic voltammetry (CV), UV−visible (UV−vis), circular dichroism (CD), and resonance Raman (λex = 406.7, 413.1 nm) spectroscopy have been used to probe the structure and redox function of horse cytochrome c (cyt c) in aqueous mixtures of three water-miscible organic solvents, specifically, acetonitrile (ACN), dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) containing 100−60% water. As the concentration of the organic solvent is increased, significant changes are observed in the spectroscopy of ferricytochrome c (ferricyt c) with the greatest structural changes observed for ferricyt c in mixed solvent media with the lowest dielectric constant (30% ACN in this work). In the UV−visible spectrum, the Soret band blue shifts (1 nm) and the intensity of the 695 nm band decreases. UV CD (185−240 nm) suggest that changes in the protein secondary structure on going from aqueous to nonaqueous media are relatively small and that the protein structure remains largely intact in nonaqueous media. In the visible C...

Reactivity of the charge transfer excited state of sodium decatungstate at the nanosecond time scale

Abstract: Previous studies have put into evidence the key role of a charge transfer excited state, noted X, in the primary steps of laser photolysis of sodium decatungstate solutions. In this work, we report a thorough study of the reactivity of the X transient towards different organic and inorganic substrates in acetonitrile and in water. The bimolecular reaction between X and the substrates is shown to occur on the nanosecond time-scale, either by H atom or electron transfer, and leads to the formation of the reduced form Y of decatungstate.We find that H atom transfer reactions are ruled by Z–H (Z=C, N, O) binding energies and lead to Y formation quantum yields that may reach the X formation quantum yield, whereas electron transfer reactions are ruled by the substrates' oxidation potential (Marcus reorganisation energy λ=1.0–1.3 eV for aromatics in acetonitrile) and lead to Y formation quantum yields similar to that obtained in the pure solvent.

Theoretical Study of the Microsolvation of the Bromide Anion in Water, Methanol, and Acetonitrile: Ion−Solvent vs Solvent−Solvent Interactions

Abstract: In this paper a theoretical study of the bromide solvation in three different polar solvents is presented: water, methanol, and acetonitrile. DFT (B3LYP) calculations on the structure and energetics of [Br(Solv)n]- clusters, for n = 1−9 and Solv = H2O, CH3OH, and CH3CN, have been carried out. Different structures where the anion is placed inside or on the surface of the cluster have been explored. The relative importance of solvent−solvent vs ion−solvent interactions determines the geometrical distribution of the microsolvation. Aggregates of solvent molecules within the bromide clusters are more defined in the case of water. Methanolated bromide clusters show a defined trend to place some solvent molecule at the second solvation shell. The bigger acetonitrile complexes (n > 5) are the more representative cases of interior complexes where the solvent molecules surround quite symmetrically the bromide anion whereas, in water and methanol, the microsolvation is more compromised between bromide−solvent and ...

Poly(Cyano-Substituted Diheteroareneethylene) as Active Electrode Material for Electrochemical Supercapacitors

Abstract: A new class of low band gap thiophene polymers prepared from (E)-α-cyanoethylene thiophene derivatives were electrochemically and physically evaluated as active electrode material for electrochemical supercapacitors. The corresponding polymers were prepared by electrochemical polymerization of these monomers from a nonaqueous solution (acetonitrile) containing tetraethylammonium tetrafluoroborate. The electrochemical properties and the stability under cyclic voltammetry of the polymers were found to be strongly dependent on their electronic configuration, especially in the case where the monomer has two different aromatic heterocycles. The range of stable electroactivity of the polymers in organic media spans about 2 V. Since poor stability was observed by cyclic voltammetry for poly-(E)-α-[(2-thienyl)methylene]-2-(3-methylthiophene)acetonitrile and poly-(E)-α-(2-thienylmethylene)-2-furanacetonitrile, only poly-(E)-α-[(2-thienyl)methylene]-2-thiopheneacetonitrile, poly-(E)-α-[(3-methyl-2-thienyl)methylene...

Pyridinolysis of phenyl-substituted phenyl chlorophosphates in acetonitrile

Abstract: The kinetics and mechanism of the reactions of phenyl-substituted phenyl chlorophosphates, I, with pyridines in acetonitrile are investigated at 25.0 °C. The rates are much faster and the transitio...

Observation of Nitrogen-Bearing Organic Molecules from Reactions of Nitrogen Atoms with Hydrocarbons: A Crossed Beam Study of N(2D) + Ethylene

Abstract: The reaction of excited atomic nitrogen, N(2D), with the simplest alkene, C2H4, has been investigated under single-collision conditions in crossed beam experiments with mass spectrometric detection. The experimental results clearly show that the N/H exchange channel leading to compounds of gross formula C2H3N is the main reaction pathway and that the reaction proceeds through the formation of a bound intermediate. The title reaction may well be regarded as a good candidate to account for the formation of acetonitrile, CH3CN, in extraterrestrial environments such as the dense atmosphere of Saturn's moon Titan where the ultimate fate of product isomers other than acetonitrile itself, that is 2H-azirine, H2C(N)CH, and ketene imine, CH2CNH, is expected to be tautomerization to the most stable structure of acetonitrile.

Structural characterization and formation mechanism of sitting-atop (SAT) complexes of 5,10,15,20-tetraphenylporphyrin with divalent metal ions. Structure of the Cu(II)-SAT complex as determined by fluorescent extended X-ray absorption fine structure.

Abstract: The UV-vis absorption spectra and the formation kinetics of sitting-atop (SAT) complexes (M(H2tpp)2+) of 5,10,15,20-tetraphenylporphyrin (H2tpp) with a series of divalent metal ions (M2+ = Mn2+, Fe2+, Co2+, Ni2+, Cu2+, and Zn2+) in acetonitrile have been investigated. The structural characteristics of the SAT complexes for a series of M2+ ions are discussed on the basis of the UV-vis absorption spectra. The structure parameters around Cu2+ in the Cu(II)-SAT complex were determined by a fluorescent EXAFS method: the coordination number is 6 with three kinds of Cu-N interactions having bond lengths of 2.05, 1.98, and 2.32 A for pyrrolenine nitrogens of H2tpp, acetonitrile nitrogens at equatorial sites, and acetonitrile nitrogens at axial sites, respectively. The rate constants at 25 degrees C for the formation of the SAT complex in acetonitrile are as follows: kf/mol-1 kg s-1 = 3.4 x 10(2) for Mn2+, 0.18 for Co2+, 1.6 x 10(-3) for Ni2+, and 61 for Zn2+. The finding that the variation trends in the rate constants for a series of M2+ ions for the SAT complex formation and the solvent exchange reaction in various solvents are very similar indicates that the rate-determining step for the SAT complex formation is the interchange between the coordinating nitrogen of a bound acetonitrile and the pyrrolenine nitrogen of H2tpp. The fact that the values of kf are smaller by 4-6 orders of magnitude in comparison with those of the solvent exchange suggests that there is a large energetic loss due to the fast preequilibria prior to the rate-determining step, such as deformation of a porphyrin ring and outer-sphere encounter formation due to an electrostatic interaction between M2+ and the local negative charge on the pyrrolenine nitrogens. We observed the subsequent formation of the corresponding metalloporphyrins by deprotonation of the SAT complex and oxidation of the M2+ center, of which the dynamic behavior was significantly different for the different M2+ ions.

Chlorophyll a self-assembly in polar solvent-water mixtures.

Abstract: The conversion of chlorophyll a (Chl a) monomers into large aggregates in six polar solvents upon addition of water has been studied by means of absorption, fluorescence spectroscopy and fluorescence lifetime measurements for the purpose of elucidating the various environmental factors promoting Chl a self-assembly and determining the type of its organization. Two empirical solvent parameter scales were used for quantitative characterization of the different solvation properties of the solvents and their mixtures with water. The mole fractions of water f1/2 giving rise to the midpoint values of the relative fluorescence quantum yield were determined for each solvent, and then various solvent-water mixture parameters for the f1/2 values were compared. On the basis of their comparison, it is concluded that the hydrogen-bonding ability and the dipole-dipole interactions (function of the dielectric constant) of the solvent-water mixtures are those that promote Chl a self-assembly. The influence of the different nature of the non-aqueous solvents on the Chl aggregation is manifested by both the different water contents required to induce Chl monomer-->aggregate transition and the formation of two types of aggregates at the completion of the transition: species absorbing at 740-760 nm (in methanol, ethanol, acetonitrile, acetone) and at 667-670 nm (in pyridine and tetrahydrofuran). It is concluded that the type of Chl organization depends on the coordination ability and the polarizability (function of the index of refraction) of the organic solvent. The ordering of the solvents with respect to the f1/2 values--methanol < ethanol < acetonitrile < acetone < pyridine < tetrahydrofuran--yielded a typical lyotropic (Hofmeister) series. On the basis of this solvent ordering and the disparate effects of the two groups of solvents on the Chl a aggregate organization, it is pointed out that the mechanism of Chl a self-assembly in aqueous media can be considered a manifestation of the Hofmeister effect, as displayed in the lipid-phase behavior (Koynova et al., Eur. J. Biophys. 25, 261-274, 1997). It relates to the solvent ability to modify the bulk structure and to distribute unevenly between the Chl-water interface and bulk liquid.

Chemistry of nickel tetrafluoropyridyl derivatives: their versatile behaviour with Brønsted acids and the Lewis acid BF3

Abstract: Treatment of trans-[NiF(2-C5NF4)(PEt3)2] (C5NF4 = tetrafluoropyridyl) (1) with HCl effects the formation of the air stable chloride complex trans-[NiCl(2-C5NF4)(PEt3)2] (2). The reaction of 2 with excess HCl slowly yields 2,3,4,5-tetrafluoropyridine (4). On reaction of 4 with [Ni(COD)(PEt3)2], the C–F activation product trans-[NiF(2-C5NF3H)(PEt3)2] (5) is formed instantly. The bifluoride compound trans-[Ni(FHF)(2-C5NF4)(PEt3)2] (6) is obtained on treatment of 1 with Et3N·3HF. Reaction of 2 with HBF4 yields the binuclear complex [NiCl{μ-κ2(C,N)-(2-C5NF4)}(PEt3)]2 (7). The X-ray crystal structure of 7 reveals a “butterfly”-shaped dimeric complex with square-planar coordination at both nickel atoms, with Ni–N distances of 1.965(4) and 1.955(4) A and Ni–C distances of 1.884(5) and 1.875(5) A. Treatment of 1 with BF3·OEt2 in the presence of acetonitrile yields the cationic compound trans-[Ni(2-C5NF4)(NCMe)(PEt3)2]BF4 (8), while reaction of trans-[Ni(OTf)(2-C5NF4)(PEt3)2] (3) with NaBAr′4 and acetonitrile gives trans-[Ni(2-C5NF4)(NCMe)(PEt3)2]BAr′4 (9) [Ar′ = 3,5-C6H3(CF3)2]. The studies reported in this paper provide methods for the synthesis of tetrafluoropyridines substituted in the 2-position and demonstrate the behaviour of nickel derivatives with Bronsted acids and the Lewis acid BF3.

Synthesis of a ligand based upon a new entry into the 3-hydroxy-N-alkyl-2(1H)-pyridinone ring system and thermodynamic evaluation of its gadolinium complex.

Abstract: The synthesis of a new, more water soluble derivative of TREN-Me-3,2-HOPO {tris[(3-hydroxy-1-methyl-2-oxo-1,2-didehydropyridine-4-carboxamido)ethyl]amine} is presented. The synthesis starts with the condensation reaction of (N-methoxyethylamino)acetonitrile hydrochloride and oxalyl chloride to give 3,5-dichloro-N-(methoxyethyl)-2(1H)-pyrazinone. The 3-position is readily substituted with a benzyloxy group, and the pyrazinone is converted to ethyl 3-(benzyloxy)-N-(methoxyethyl)-2(1H)-pyridinone-4-carboxylate by a Diels−Alder cycloaddition with ethyl propiolate. Basic deprotection of the ester followed by activation, coupling to tren, and acidic deprotection of the benzyl groups gives the ligand TREN-MOE-3,2-HOPO {tris[(3-hydroxy-1-(methoxyethyl)-2-oxo-1,2-didehydropyridine-4-carboxamido)ethyl]amine}. The gadolinium complex of TREN-MOE-3,2-HOPO was prepared by metathesis, starting from gadolinium chloride. The solubility of the new metal complex is significantly enhanced. The four protonation constants (det...

Effect of Protic Cosolvents on the Photooxygenation of Diethyl Sulfide

Abstract: The sluggish (kr < 10kq) photooxygenation of diethyl sulfide in both benzene and other aprotic solvents such as acetone and acetonitrile is made efficient by addition of small amounts of alcohols and, with a much more conspicuous increase, of phenols and carboxylic acids (≪0.1% additive is sufficient in this case). A kinetic analysis shows that the effect is accounted for by interaction of the protic additives with the first formed intermediate, the persulfoxide, in competition with cleavage to the components. The thus obtained rate constants kH linearly correlate with the acid strength of the additives, and the effect is rationalized as a general acid catalysis. Hydrogen bonding of the persulfoxide under this condition accounts in an economic way for the observed data, including co-oxygenation of Ph2SO in mixed solvents.

Calix[4]arenes as Selective Extracting Agents. An NMR Dynamic and Conformational Investigation of the Lanthanide(III) and Thorium(IV) Complexes

Abstract: The lanthanide and Th4+ complexes with calix[4]arene ligands substituted either on the narrow or at the wide rim by four coordinating groups behave totally differently as shown by an NMR investigation of the dia- and paramagnetic complexes. Solutions of complexes were prepared by reacting anhydrous metal perchlorate salts with the ligands in dry acetonitrile (CAUTION). Relaxation time T1 titrations of acetonitrile solutions of Gd3+ by calixarenes indicate that ligands subsituted on the narrow rim form stable 1:1 complexes whether they feature four amide groups (1) or four phosphine oxide functions. In contrast, a ligand substituted by four (carbamoylmethyl)-diphenylphosphine oxide moieties on the wide rim (3) and its derivatives from polymeric species even at a 1:1 ligand/metal concentration ratio. Nuclear magnetic relaxation dispersion (NMRD) curves (relaxation rates 1/T1 vs magnetic field strength) of Gd3+, Gd3+.1 and Gd3+.3 perchlorates in acetonitrile are analyzed by an extended version of the Solomon-Bloembergen-Morgan equations. A comparison of the calculated rotational correlation times tau r shows that ligand 3 forms oligomeric Gd3+ species. The chelates of ligand 1 are axially symmetric (C4 symmetry), and the paramagnetic shifts induced by the Yb3+ ion are accounted for quantitatively. The addition of water or of nitrate ions does not modify the geometry of the complex. The metal chelates of 3 and its derivatives adopt a C2 symmetry, and the paramagnetic shifts are interpreted on a semiquantitative basis only. Water and NO3- ions completely labilize the complexes of the heavy lanthanides. The very high selectivity of ligand 3 through the lanthanide series stems from a complex interplay of factors.

Excited-state dynamics and photophysical properties of para-aminobenzophenone

Abstract: The photophysical properties of the singlet (S1) and triplet (T1) excited states of p-aminobenzophenone (p-ABP) have been investigated in various organic solvents using steady-state as well as transient absorption spectroscopy with picosecond and subpicosecond time resolution. p-ABP is weakly fluorescent in benzene as well as in polar aprotic solvents, acetonitrile, DMSO, and DMF, but nearly nonfluorescent in cyclohexane and methanol. In cyclohexane, the S1 state has the nπ* configuration and is short-lived [τ(S1) ∼ 12 ps]. In methanol, a polar and protic solvent, the S1 state is much shorter-lived [τ (S1) 100 ps). The triplet yield is much higher in nonpolar solvents than in polar solvents but the lifetime shows the rever...

Electrochemical Studies of C60/Pd Films Formed by the Reduction of C60 in the Presence of Palladium(II) Acetate Trimer. Effects of Varying C60/Pd(II) Ratios in the Precursor Solutions

Abstract: Cyclic voltammetric studies of the electrochemical formation and redox properties of C60/Pd films are reported. Films used in this work are generated under multicyclic scans in an acetonitrile/toluene (1:4, v/v) mixture containing fullerene C60 and palladium(II) acetate trimer as the film precursors and tetra(n-butyl)ammonium perchlorate as supporting electrolyte. The structure and electrochemical properties of the deposited layers depend on the relative concentrations of the precursors (C60 and {Pd(OAc)2}3) present in the growth solution. In the presence of excess palladium(II) acetate trimer, palladium, as well as the redox active film, is deposited, as shown by electrochemical studies of the behavior of the modified electrodes toward hydrogen evolution and palladium oxidation in aqueous acidic solution. At very negative potentials, all of the films decompose which is presumed to be due to the repulsive interaction between negatively charged C60 centers and mechanical strain induced by the incorporation...

Electrochemical Modification of Poly(3-(4-Fluorophenyl)thiophene)

Abstract: The chlorination and regeneration of poly(3-(4-fluorophenyl)thiophene) (PFPT) thin films has been investigated using cyclic voltammetry, energy dispersive analysis by X-ray, and X-ray photoelectron spectroscopy. A complete substitution of all 4-thiophene positions of the electrodeposited polymer is achieved by electrochemical oxidation in the presence of chloride ions. The resulting inactive chlorinated polymer is then reactivated by p-doping in acetonitrile containing 0.5 M Et4NBF4. The n-doping of this electroactive chlorinated polymer is not possible because the electrochemical reduction induces the departure of the chloride atoms, leading to the regeneration of the parent PFPT in the electroactive form.