Cationic Acceptor Research Articles

Pentamethylcyclopentadienyl organoiron(II) hydrazone complexes: Synthesis, spectroscopic characterization, and second-order nonlinear optical properties. X-ray crystal structure of [formula omitted

A series of novel pentamethylated sandwich complexes based on the [Cp ∗Fe(η 6-C 6H 5)] + core (Cp ∗ = η 5-C 5Me 5) has been prepared. The new organometallic π-conjugated push–pull chromophores [ Cp ∗ Fe ( η 6 - C 6 H 5 ) -NHN CHR ] + PF 6 - (R = 2,4,6-Me 3C 6H 2, 4; (η 5-C 5H 5)Fe(η 5-C 5H 4), 5) were prepared through condensations between the organometallic hydrazine precursor [ Cp ∗ Fe ( η 6 - C 6 H 5 NHNH 2 ) ] + PF 6 - ( 3), and either the mesitaldehyde or the ferrocenecarboxaldehyde, respectively. Their original design combines the cationic mixed sandwich acceptor (A) associated with an organic or organometallic donor (D) through the asymmetric hydrazone spacer –NH–N CH–. The mesityl ring of 4 has been complexed by the arenophile Cp ∗Ru +, leading to the first η 6:η 6-coordinated dinucleating hydrazone complex, [ Cp ∗ Fe ( η 6 - C 6 H 5 ) -NHN CH- { ( η 6 - 2 , 4 , 6 - Me 3 C 6 H 2 ) Ru Cp ∗ } ] 2 + [ PF 6 - ] 2 ( 6). Both the mono- and dinuclear hydrazones were stereoselectively obtained as their trans-isomers about the N C double bond. All the new compounds were thoroughly characterized by a combination of elemental analysis and spectroscopic techniques ( 1H and 13C NMR, IR and UV–Vis). In addition, the solid-state structure of the organometallic hydrazine precursor 3 has been determined by X-ray diffraction study. Spectroscopic and electrochemical data of the organometallic hydrazones 4 and 5 clearly indicate a mutual donor–acceptor electronic influence resulting from conjugation between the end groups through the entire hydrazone backbone. Compounds 4 and 5 are strongly polarized D–π–A systems exhibiting low-lying intramolecular charge transfer bands in their electronic absorption spectra and enhanced second-order NLO properties (μβ), as measured by EFISH technique at 1.907 μm.

How Ionic Are Room-Temperature Ionic Liquids? An Indicator of the Physicochemical Properties

Room-temperature ionic liquids (RTILs) are liquids consisting entirely of ions, and their important properties, e.g., negligible vapor pressure, are considered to result from the ionic nature. However, we do not know how ionic the RTILs are. The ionic nature of the RTILs is defined in this study as the molar conductivity ratio (Lambda(imp)/Lambda(NMR)), calculated from the molar conductivity measured by the electrochemical impedance method (Lambda(imp)) and that estimated by use of pulse-field-gradient spin-echo NMR ionic self-diffusion coefficients and the Nernst-Einstein relation (Lambda(NMR)). This ratio is compared with solvatochromic polarity scales: anionic donor ability (Lewis basicity), E(T)(30), hydrogen bond donor acidity (alpha), and dipolarity/polarizability (pi), as well as NMR chemical shifts. The Lambda(imp)/Lambda(NMR) well illustrates the degree of cation-anion aggregation in the RTILs at equilibrium, which can be explained by the effects of anionic donor and cationic acceptor abilities for the RTILs having different anionic and cationic backbone structures with fixed counterparts, and by the inductive and dispersive forces for the various alkyl chain lengths in the cations. As a measure of the electrostatic interaction of the RTILs, the effective ionic concentration (C(eff)), which is a dominant parameter for the electrostatic forces of the RTILs, was introduced as the product of Lambda(imp)/Lambda(NMR) and the molar concentration and was compared with some physical properties, such as reported normal boiling points and distillation rates, glass transition temperature, and viscosity. A decrease in C(eff) of the RTILs is well correlated with the normal boiling point and distillation rate, whereas the liquid-state dynamics is controlled by a subtle balance between the electrostatic and other intermolecular forces.

P‐type conductive CuYO2 phosphor Co‐doped with Eu, Tb or Tm rare‐earth cation and Ca acceptor cation

AbstractIn delafossite‐type oxides of CuRx Y1–x O2 (R = Eu, Tb or Tm) and CuRx Cay Y1–x –y O2 prepared through the conventional solid state reactions, the lattice constant dependence on the composition implies doping with the Tb3+, Eu3+ and Tm3+ cations on the Y3+ site. Noticeable sharp emission lines due to the f–f transitions of Eu3+, Tb3+ and Tm3+ are observed at room temperature in CuRx Cay Y1–x –y O2 as well as CuRx Y1–x O2. P‐type conductivity of CuRx Cay Y1–x –y O2 increases with increasing Ca concentration, indicating the increase of hole concentration caused by doping with Ca2+ acceptor cation on the Y3+ site. These results indicate the controllability of the luminescence and conductivity in delafossite‐type CuYO2 oxides by co‐doping with Eu, Tb or Tm rare‐earth cation and Ca acceptor cation on the Y3+ sites. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Kinetic investigations of the mechanism of dihydrogen driven catalytic reduction of methylene blue, safranine O, methyl viologen and ferricyanide using platinum carbonyl cluster anions (Chini-clusters) as catalyst

[Bu 4N] 2[Pt 12(CO) 24] ( 1) catalyses the selective reduction of electron acceptors ( S), methylene blue (MB +), safranine O (Saf +), methyl viologen (MV 2+) and ferricyanide by dihydrogen. Macroscopic rate investigations for the cationic substrates in DMF, and for ferricyanide in DMSO have been carried out. In all cases, k obs is given by k 1 [ S] + k 2, indicating that there are two catalytic cycles. In one of them, the formation of a complex between S and [Pt 12(CO) 24] 2− in the rate determining step (rate constant k 1) is followed by electron transfer and/or other fast steps. In the other catalytic cycle, the rate determining step (rate constant k 2) involves formation of the solvated cluster anion [Pt 12(CO) 24] 2−. The solvated cluster then undergoes fast reduction by dihydrogen and other reactions. The relative contributions of these two cycles depend on the substrate, and for MB +, Saf +, MV 2+ and [Fe(CN) 6] 3− the contribution of the second cycle is about 99%, 55%, 77% and 97%, respectively. Both k 1 and k 2 of ferricyanide are about three orders of magnitude smaller than those of the cationic electron acceptors. The rates of reduction of MB + and Saf + have also been studied in the presence of added water. Rates increase as the presence of water provides an additional pathway for the reduction of [Pt 12(CO) 24] 2− to [Pt 9(CO) 18] 2−.

Organic rectifying junctions fabricated by ionic coupling

Ionically-assembled structures that comprise discrete layers of cationic acceptors (4,4'-bipyridinium) and anionic donors (copper phthalocyanine-3,4',4'',4'''-tetrasulfonate) exhibit asymmetric current-voltage (I-V) characteristics with high rectification ratios of 60-100 at +/-1 V.

Effect of the Molecular Weight and the Ionic Strength on the Photoluminescence Quenching of Water-Soluble Conjugated Polymer Sodium Poly[2-(3-thienyl)ethyloxy-4-butylsulfonate

The photoluminescence (PL) quenching of sodium poly[2-(3-thienyl)ethyloxy-4-butylsulfonate)] (PTE-BS) by the cationic electron acceptor methyl viologen (MV2+) was investigated in samples with high (HPTE-BS) and low (LPTE-BS) molecular weight. The Stern−Volmer constant decreases with decreasing the molecular weight from 8.4 × 105 M-1 down to 2.4 × 104 M-1. This decrease is attributed to the lower concentration of the polyanion in the solution of LPTE-BS due to the lower solubility of this polymer when compared with HPTE-BS. Furthermore, we demonstrate that lowering HPTE-BS solubility by increasing the solution ionic strength affects the PL and the quenching mechanism. For the four salts investigatedNaCl, KCl, MgCl2, and CaCl2the photoluminescence decreases with increasing the ionic strength, and the effect is conspicuous for the divalent cations investigated. The linear behavior characteristic of the quenching of the HPTE-BS luminescence by MV2+ disappears when the quenching is performed in the solution of CaCl2 with ionic strength 0.3 M, which points to the formation of polymer aggregates due to the electrostatic bridging between monomers helped by the divalent cations introduced in the solution.

Quenching of singlet photoexcited state of water soluble phthalocyanines and porphyrins by viologens interacting electrostatically

Quenching of photoexcited anionic and water-soluble phthalocyanines and 5,10,15,20-tetraarylporphyrins by viologens has been investigated. It was confirmed that the quenching of the singlet photoexcited state takes place, and that the mechanism is mostly a static one due to electrostatic interaction between the donor and the acceptor. The static mechanism was analyzed by curve-fitting of the relative emission intensity vs viologen concentration resulting in four kinds of mechanisms composed of static quenching accompanied partly by a dynamic one. The static mechanism was classified into two types: one mechanism is due to 1:n electrostatic interaction of the anionic sensitizer and the cationic acceptor, and other is a Perrin type for which the acceptor is incorporated into the quenching sphere around the sensitizer according to a Poisson distribution. The effect of micelles for the quenching was also studied including the effect of viologen with a long alkyl chain. The ionic micelles either incorporated or repulsed the ionic sensitizer and accepter resulting in either static quenching or prohibition of the quenching. Cationic phthalocyanines and porphyrins were also examined for the reaction with cationic viologens.

Electron‐Transfer‐Initiated Cascade Cyclizations of Terpenoid Polyalkenes in a Low‐Polarity Solvent: One‐Step Synthesis of Mono‐ and Polycylic Terpenoids with Various Functionalities

AbstractA methodology for the one‐step synthesis of cyclic polyalkene terpenoids in a low‐polarity solvent (dichloromethane) by photoinduced electron transfer (PET) is described. For the efficiency of such processes in low‐polarity solvents, the use of the cationic electron acceptor N‐methylquinolinium hexafluorophosphate is vital. The first direct cyclizations of farnesol and geranylgeraniol to the corresponding all‐trans‐fused 6,6‐ and 6,6,6‐cyclic products are also reported. The mechanism of the termination of the cyclizations is also discussed, isotope‐labeling experiments having shown that it proceeds through reduction of the final radical to the corresponding anion, followed by protonation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

New lanthanide complexes for sensitized visible and near-IR light emission: synthesis, 1H NMR, and X-ray structural investigation and photophysical properties.

We describe the syntheses, the 1H NMR studies in CD3OD and D2O as solvent, the X-ray characterization, and the luminescence properties in D2O solution of the two complexes Eu.1 and Er.1, where 1 is a dipartite ligand that includes (i) a 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A) unit serving as hosting site for the metal center; and (ii) a phenanthroline unit which plays the role of light antenna for the sensitization process of the metal centered luminescence. In a previous report (Inorg. Chem. 2002, 41, 2777), we have shown that for Eu.1 there are no water molecules within the first coordination sphere. X-ray and 1H NMR results reported here are consistent with full saturation of the nine coordination sites within the Eu.1 and Er.1 complexes. In addition, these studies provide important details regarding the conformations, square antiprism (SAP) and twisted square antiprism (TSAP), adopted in solution by these complexes. The luminescence results are consistent with both an effective intersystem crossing (ISC) at the light absorbing phenanthroline unit (lambda(exc) = 278 nm) and an effective energy transfer (en) process from the phenanthroline donor to the cation acceptor (with unit or close to unit efficiency for both steps). In D2O solvent, the overall sensitization efficiency, phi(se), is 0.3 and 5 x 10(-6), for Eu.1 (main luminescence peaks at 585, 612, 699 nm) and Er.1 (luminescence peak at 1530 nm), respectively. The photophysical properties of both complexes are discussed with reference to their structural features as elucidated by the obtained 1H NMR and X-ray results.

Cationic Borabenzene Complexes as Electron Accepting Groups for Molecular Material with Nonlinear Optical Properties

AbstractThe dinuclear dipolar borabenzene complexes [(η5‐C5H5)Fe{μ‐(η5‐C5H4)C2(η6‐BC5H5)}ML]X [ML = Ru(η6‐C6H6), X = Cl (4aCl), PF6 (4aPF6), B(C6H5)4 (4aBPh4); ML = Rh(η5‐C5Me5), X = Cl (4bCl), PF6 (4bPF6); ML = Ir(η5‐C5Me5), X = Cl (4cCl), PF6 (4cPF6)] were synthesized by a nucleophilic substitution reaction of the trimethylphosphane adduct of borabenzene (1) with lithium ferrocenylacetylide, subsequent lithium‐thallium exchange and coordination of the appropriate ML unit obtained from [Ru(η6‐C6H6)Cl(μ‐Cl)]2, [M(η5‐C5Me5)Cl(μ‐Cl)]2 (M = Rh, Ir); the formed chloride salts, which are soluble in water, were transformed to the PF6 salts by adding [NH4][PF6] to the corresponding water solution. BPh4 salts can be produced, when a methanolic solution of Na[BPh4] were added to CH2Cl2‐solutions of the appropriate PF6 salt. X‐ray structure analyses of single crystals of 4aBPh4 and 4bPF6 were successful, illustrating the cation 4a+ in an ideal cis‐conformation, whereas 4b+ displays a cis‐ and trans‐conformation. Spectroscopic and cyclic voltammetry studies reveal a small but distinct donor‐acceptor interaction between the ferrocenyl donor and the cationic borabenzene complex acceptor which increases in the order 4aPF6 < 4cPF6 < 4bPF6. The nonlinear optical properties of these donor‐acceptor complexes were studied by means of hyper‐Rayleigh scattering (HRS), resulting in the determination of small values for the first hyperpolarisability ß, which increase in the same order as the donor‐acceptor interaction.

The heme domain of cellobiose oxidoreductase: a one-electron reducing system

Phanerochaete chrysosporium cellobiose oxidoreductase (CBOR) comprises two redox domains, one containing flavin adenine dinucleotide (FAD) and the other protoheme. It reduces both two-electron acceptors, including molecular oxygen, and one-electron acceptors, including transition metal complexes and cytochrome c. If the latter reacts with the flavin, the reduced heme b acts merely as a redox buffer, but if with the b heme, enzyme action involves a true electron transfer chain. Intact CBOR fully reduced with cellobiose, CBOR partially reduced by ascorbate, and isolated ascorbate-reduced heme domain, all transfer electrons at similar rates to cytochrome c. Reduction of cationic one-electron acceptors via the heme group supports an electron transfer chain model. Analogous reactions with natural one-electron acceptors can promote Fenton chemistry, which may explain evolutionary retention of the heme domain and the enzyme's unique character among secreted sugar dehydrogenases.

Defect association in acceptor-doped SrTiO3: case study for Fe′TiV˙˙O and Mn″TiV˙˙O

The association of acceptor cations (Fe′Ti and Mn″Ti) with oxygen vacancies in Fe- and Mn-doped SrTiO3 single crystals is investigated using in-situ EPR spectroscopy. Effective association enthalpies ΔassH0eff and entropies ΔassS0eff are determined, and ΔassH0eff is found to depend strongly on the dopant concentration. This dependence can be roughly described by a correction term in the chemical potential that is proportional to the cube root of the defect concentration. Extrapolation to infinite dilution yields an association enthalpy of −26 kJ mol−1. The association of oxygen vacancies can significantly reduce the ionic conductivity of these materials at temperatures up to ca. 200 °C (Fe′Ti) or even higher (Mn″Ti), and must therefore be taken into account in the respective defect chemical models at moderate or low temperatures.

Molecular structures of cation...pi(arene) interactions for alkali metals with pi- and sigma-modalities.

The monovalent cations of Na(+), K(+), Rb(+), and Cs(+) derived from the highly electropositive alkali metals represent prototypical charged spheres that are mainly subject to relatively simple electrostatic and solvation (hydration) forces. We now find that the largest of these Rb(+) and Cs(+) are involved in rather strong cation...pi(arene) interactions when they are suitably disposed with the ambifunctional hexasubstituted benzene C(6)E(6). The ether tentacles (E = methoxymethyl) allow these cations to effect eta(1)-bonding to the benzene center in a manner strongly reminiscent of the classical sigma-arene complexes with positively charged electrophiles where Z(+) = CH(3)(+), Br(+), Cl(+), Et(3)Si(+), etc. The somewhat smaller potassium cation is involved in a similar M(+)...pi(arene) interaction that leads to eta(2)-bonding with the aromatic center in the pi-mode previously defined in the well-known series of silver(I)/arene complexes. We can find no evidence for significant Na(+)... pi(arene) interaction under essentially the same conditions. As such, the sigma-structure of the Rb(+) and Cs(+) complexes and pi-structure of the K(+) complex are completely integrated into the continuum of sigma-pi bondings of various types of electrophilic (cationic) acceptors with arene donors that were initially identified by Mulliken as charge-transfer.

Alignment of chevron-shaped molecules for photonic and electronic applicationsElectronic supplementary information (ESI) available: synthetic details and analytical data for three chevron-shaped molecules. See http://www.rsc.org/suppdata/jm/b2/b201801m/

A novel method is reported whereby unconventional molecules without aliphatic tails may be non-centrosymmetrically aligned by the Langmuir–Blodgett technique, the molecules in this case having a central cationic acceptor and two π-bridged donor groups with an angle of ca. 120° between the charge-transfer axes of the chevron-shaped D-π-(A+)-π-D unit. Their LB films exhibit second-harmonic generation and molecular rectification.

Syntheses and Magnetic Property of the Salts of Positively-Charged Verdazyl Radicals and TCNQF 4 − Anion Radical

Three kinds of (1:1) salts of TCNQF 4 anion with 3-(4-trimethylaminophenyl)-1,5-diphenyl-6-oxo-verdazyl radical cation [1 + ] and its mono-methyl [2 + ] and di-methyl [3 + ] derivatives have been prepared, and magnetic property and crystal structure of the salts have been studied. The salts were found to be new genuine organic magnetic compounds consisting of open-shell verdazyl radical cation and electron acceptor TCNQF 4 anion.

Cellular automaton simulation of a simple corrosion mechanism: mesoscopic heterogeneity versus macroscopic homogeneity

A cellular automaton model that simulates the mesoscopic scale behavior of an electrode is presented in this article. Transition rules that mimic anodic and cathodic events corresponding to a simple dissolution mechanism including the presence of adsorbates and charge acceptor cations are introduced. The model focuses essentially on the case of a free corroding electrode, although polarized regimes are also examined. This mesoscopic approach discloses features that are not considered in the standard macroscopic description. First, the metal surface becomes morphologically heterogeneous. Secondly, the degree of roughness is linked to a specific distribution of active dissolution sites, and the resulting interplay between morphology and kinetics carries with it a local segregation of reactants and the detachment of clusters of varying size. Issues concerning these distinguishing properties of the electrode surface are examined using morphogenetic descriptors. Mesoscopic balance equations are established and compared with the macroscopic standard equations for an homogeneous electrode. The influence of those purely mesoscopic features is addressed. We conclude that, although both the descriptions are different, they coexist consistently if a proper approach is chosen.

Molecular Species Disturbing the Fluid–Solid Phase Transition of Nitrogen Adsorbed on Graphite: Importance of Aromaticity

The fluid-solid (FS) phase transition of N2 adsorbed on graphite is known to be depressed abnormally by conjugated coplanar molecules such as benzene and copper phthalocyanine. This paper describes an investigation of the influence of a non-aromatic conjugated species (1,3-butadiene), a non-aromatic cation acceptor (18-crown-6), a strong electron donor (tetrathiafulvalene) and a strong electron acceptor (tetracyanoquinodimethane) on the FS phase transition of N2, when they were preplated on graphite. These species were, in fact, found to have no significant effect. This implies that molecular properties such as cation acceptance and electron transfer are of no importance, whereas the aromaticity of co-existing species plays a crucial role in disturbing the phase behaviour of N2.

Photoluminescence of Water-Soluble Conjugated Polymers: Origin of Enhanced Quenching by Charge Transfer

Quenching of the photoluminescence (PL) emission from conjugated macromolecules by charge transfer to cationic electron acceptors is studied by changing the ion concentration in buffered aqueous solutions, by changing the concentration of acceptors, and by varying the temperature. A weakly bound complex is formed (in water) between polyanionic conjugated macromolecules and cationic electron acceptors with Coulomb binding energy ∼150 meV. The mean distance between the polymer(-) and quencher(+) was estimated as 10 Å, consistent with the effective charge-transfer distance. At high quencher concentrations, quenching by acceptors within the sphere-of-action becomes important; a modified Stern−Volmer equation is used to estimate the radius (∼400 Å). High-temperature studies of concentrated quencher solutions independently indicate a crossover from static quenching to sphere-of-action quenching with a radius ∼400 Å. Since the radius is comparable to the radius of gyration of the macromolecule, the high molecular weight of the conjugated polymer enhances the quenching.

Light- and pH-driven electron transfer in the pyranine–methylviologen system

A face-to-face electrostatic complex is formed in alkaline solution by pairing the trisodium salt of 8-hydroxy-1,3,6-pyrenetrisulfonic acid (pyranine tsPyOH,3Na +), an anionic donor, with the dichloride salt of methyl viologen (MV 2+, 2Cl −), a cationic acceptor. The donor displays dual properties: it can be photoionized or can transfer an electron to the acceptor. It is shown that light absorption by the self-assembled complex leads to the formation of a particularly short-lived species (3.7 ps) assigned to a singlet excited state which relaxes to the ground state via a charge-transfer state.

Chalcone-Analogue Dyes Emitting in the Near-Infrared (NIR): Influence of Donor−Acceptor Substitution and Cation Complexation on Their Spectroscopic Properties and X-ray Structure

The photophysical properties of several newly synthesized 1-benzothiazole-3-(4-donor)-phenyl-substituted prop-2-en-1-ones (substituted chalcones) are studied as a function of solvent polarity, temperature, and metal ion by employing steady-state and time-resolved spectroscopy. To investigate the effect of bulkiness and donor strength of the anilino moiety on the spectroscopic properties of these dyes, the spectroscopic behavior of the 4-N-dimethylamino (DMA), the 4-N-tetraoxa-monoaza-15-crown-5 (A15C5), and the 4-N-tetrathia-monoaza-15-crown-5 (AT415C5) derivatives as well as the 3-julolidino (Jul) analogue is compared. Absorption and fluorescence measurements reveal that the strength of the intramolecular charge transfer (ICT) process increases on the order of AT415C5 < A15C5 ∼ DMA < Jul. The slight but significant differences between the two crowned dyes are well-supported by the results of the X-ray structure analysis, where oxa aza and thia aza crowns show essentially different geometries. For both fl...