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A series of D-π-A, D-π-D'-π-A, D-π-A'-π-A nonlinear optical chromophores with vinylene π-electron bridges or bridges with π-deficient/π-excessive heterocyclic moieties along with the corresponding precursors D-vinylene, D-π-D', D'-π-A, D-π-A' and A'-π-A are synthesized and studied both experimentally and computationally. The effect of the heterocycle in the π-electron bridge on the oxidation/reduction potentials and the energy gap (ΔEel ) is investigated in detail. The properties of the D-π-A'(D')-π-A chromophores are shown to correlate with those of building blocks: the oxidation potential is determined by the D-vinylene, and the reduction potential is determined by A'(D')-π-A truncated compounds. The contribution of the acceptor to the oxidation potential of chromophores in comparison with those of the precursors was estimated and analyzed in terms of electronic communication between the end groups. A good correlation between the ΔEel and the chromophores' first hyperpolarizability is revealed.

Recent achievements of electrochemical efficient and atom-economical catalytic methods for the formation of aromatic carbon-phosphorus bonds are summarized in this mini-review. Electrochemical reac...

This paper elucidates the redox properties and reactivity of a number of cyclometalated nickel(II) complexes in oxidation processes. Original and robust procedures for the synthesis of nickelacycles with two cyclometalated moieties and halogenated nickelacycles were developed. The complexes were studied by means of electrochemical, ESR, DFT, and single-crystal XRD methods. Notable features of the nickelacycles are unusually low oxidation potentials. Upon electrochemical oxidation the complexes produce carbon–carbon and carbon–heteroatom coupled products, the ratio of which can be tuned by the conditions applied.

For the first time the nonlinear optical (NLO) activity of indolizine-based push-pull chromophores with different acceptor moieties was studied and compared. All the chromophores demonstrate strong absorption band in the visible (orange-red) part of the spectrum, with e of ca. 105 L∙cm−1∙M−1 notably dependent on medium polarity. Replacement of Ph-TCF acceptor by Hex-TCP one results in twofold increase of the first hyperpolarizability value. Energy gaps estimated by electrochemical methods decrease in the series ΔE1a,b>ΔE3a,b>ΔE2a,b for compounds with Ph-TCF, DCM and Hex-TCP acceptors, respectively, good agreement with DFT estimations is obtained. The nonlinear optical coefficient for poled PMMA-based films, containing 20 wt% of isomeric indolizine chromophores with weaker dicyanomethylene (DCM) acceptor and with π- bridge expanded by isophorone moiety, achieves 36 pm/V, thus exceeding those for materials containing chromophores with stronger Ph-TCF or Hex-TCP acceptors and with short vinylene π-bridge.

The two-electron reduction of some Ni(II) complexes with α-diimine ligands ([Ni(bpy)3]2+ and [Ni(pybox)2]2+) at a platinum electrode from acetonitrile (AN) and dimethylformamide (DMF) solutions is investigated by cyclic voltammetry (CV). Digisim simulations are employed to determine kinetic parameters. For [Ni(bpy)3]2+ in AN the first electron transfer (ET) step was found to be rate-controlling. The rate constants of the first and second steps (k1 and k2) are practically the same in the DMF solution. In contrast, the second ET step is rate controlling for the [Ni(pybox)2]2+ complex in AN, while the difference between k1 and k2 for this complex reactant in DMF becomes less noticeable. Molecular modeling based on the quantum mechanical theory of electron transfer and on density functional theory (DFT) calculations is performed for the first time to predict the activation barriers of the two-step heterogeneous redox processes and to elucidate the role of the ligands and solvents in the kinetics of these processes. Three-dimensional reaction free energy surfaces are constructed along the solvent and intramolecular coordinates. The electronic transmission coefficients are estimated as well. The results of model calculations are in qualitative agreement with the experimental data.

A method of synthesis of a new class of push-pull chromophores with vinylquinoxalinone conjugated bridges has been proposed; two isomeric pairs of chromophores with dimethyl aniline donor and dicyanovinyl or tricyanofuran acceptors linked via vinyl-7(6)-quinoxalinon-3-yl or vinyl-7(6)-quinoxalinone-3-vinyl bridges, correspondingly, have been synthesized and systematically investigated. The solvatochromic behavior, thermal stability and electrochemical properties were studied to establish the structure-property relationships. Chromophore 7-DMA-VQ on V-TCF exhibits the minimal HOMO-LUMO energy gap (ΔE 0.84 eV) and the highest thermal stability (T d = 313 °C).

Data provided by electrochemical studies are of particular interest for nonlinear optical chromophores being used to predict the properties and search more effective donor-acceptor systems. Based on voltammetric experiments (CV, DPV), one can estimate the HOMO and LUMO energy gap and correlate it with the structure, analyze solvatochromic effects, and obtain additional important information about changes in the energy of each molecular orbital, and not only the gap itself (an advantage over optical methods). Also, the location of the gap relative to the energy axis (electrochemical electronegativity) allows to identify the more hyperpolarizable chromophores. This review summarizes the results obtained in recent years in the field of chromophore electrochemistry elucidating the relationship between molecular NLO characteristics predicted on the basis of quantum-chemical calculations (the hyperpolarizability) and energy characteristics of promising chromophores.

The electrochemical and electrophysical properties of fullerene C 60 derivatives containing an amino group at the methanofullerene bridging carbon atom and a tetrahydropyridine moiety annelated to the fullerene have been determined. The electrochemical reduction of the derivatives was found to proceed less easily than that of C 60 but more easily than that of unsubstituted methano- and pyrrolidinofullerenes.

A series of diphosphonate-bridged dipalladacycles [(phpy)Pd(EtO)2P(O)]2, [(bhq)Pd(EtO)2P(O)]2, [(phpz)Pd(EtO)2P(O)]2 (phpy=2-phenylpyridine, bhq=benzo[h]quinoline, phpz=1-phenylpyrazole), which are known to be involved in catalytic C–H phosphonation reactions, was prepared and characterized by NMR spectroscopy and cyclic voltammetry in acetonitrile solutions and in carbon paste electrode. Diphosphonate dipalladacycles are oxidized irreversibly at more positive potentials as distinguished from related acetate palladacycles. Electrochemical preparative oxidations carried out under mild conditions without any specially added oxidants quantitatively afforded corresponding arylphosphonates. For complete conversion of dipalladacycles into arylphosphonates, four electrons per each palladium atom are required, that probably indicates a mechanism involving Pd(IV)/Pd(II) redox couple.

Principal achievements and modern trends in the development of new methods of electrocatalytic fluoroalkylation are analysed and generalised. Possibilities and advantages of the electrochemical preparation of fluoroalkyl compounds are demonstrated. The attention is focused on the fluoroalkylation of olefins, σ-fluororganonickel complexes reactivity, aromatic perfluoroalkylation, fluoroalkyl phosphines and phosphine oxides synthesis, ligand directed C–H-fluoroalkylation.

Novel versatile electrocatalytic route for obtaining fluoroalkylated phosphines and phosphine oxides from white phosphorous or diphenylchlorophosphine is discussed. This process occurs under electrochemical generation of nickel complexes in low oxidation state during undivided electrolysis of organofluorine iodides and phosphorous-containing substrate in mild conditions without supporting electrolyte.

The electochemical oxidation of palladium acetate or palladium perfluoroacetate in the presence of 2-phenylpyridine promotes catalytic ortho C–H substitution reactions. As possible intermediates, Pd(II) metallacycles with Pd-bound acetate, perfluoroacetate, and perfluoroheptanoate substituents have been isolated and characterized: binuclear [(PhPy)Pd(μ-OAc)]2 and [(PhPy)Pd(μ-TFA)]2 and mononuclear [(PhPy)Pd(TFA)](CH3CN), [(PhPy)Pd(TFA)](PhPy), and [(PhPy)Pd(PFH)](PhPy). The fluorinated derivatives were found to exist in solvent-dependent equilibria between mononuclear and binuclear forms. Cyclic voltammetry was used to elucidate redox properties of the palladacycles and the oxidation route to the final products.

A series of diverse binuclear and mononuclear cyclometalated palladium(II) complexes of different structure was investigated by electrochemical techniques combined with density functional theory (DFT) calculations. The studies including cyclic and differential pulse voltammetry, X-ray structure analysis and quantum chemical calculations revealed a regularity of the complexes oxidation potential on the metal–metal distance in the complexes: the larger Pd–Pd distance, the higher oxidation potentials. The reduction potentials feature unusually high negative values while no correlation depending on the structure could be observed. These results are in a good agreement with the electron density distribution in the complexes. Additionally, ESR data obtained for the complexes upon oxidation is reported.

A one-step catalytic method for the ortho-fluoroalkylation of 2-phenylpyridine has been developed that employs the less-commonly used higher oxidation states of nickel or palladium by electro-oxidation of stable MII precursors.

Principal achievements and modern trends in the development of new methods of electrocatalytic fluoroalkylation are analysed and generalised. Possibilities and advantages of the electrochemical preparation of fluoroalkyl compounds are demonstrated. The attention is focused on the fluoroalkylation of olefins, σ-fluororganonickel complexes reactivity, aromatic perfluoroalkylation, fluoroalkyl phosphines and phosphine oxides synthesis, ligand directed C–H-fluoroalkylation.

Electrolysis of organofluorine iodides and white phosphorus or diphenylchlorophosphine in the presence of a Ni-catalyst results in the formation of fluoroalkyl phosphines.