Mononuclear copper(II) complexes containing a macrocyclic ditopic ligand: synthesis, structures and properties

International audienceThree different mononuclear copper(II) complexes 1-3 bearing ditopic macrocyclic ligands (L1 or L2) have been prepared. Both ligands include two coordinating cores, namely tris(methylpyridyl)amine (TPA) and pyridine-dicarboxamide (PydCA). Complexes 1-3 have been characterized in solid state, and in solution by UV-Vis and EPR spectroscopies, as well as by cyclic voltammetry. X-ray diffraction analyses of crystals of complexes 1 and 3 show that the Cu(II) ion is preferably coordinated in the TPA site. Moreover, the coordination sphere of the copper center fully depends on the Cu(II) salt used for the synthesis (CuCl2 for 1 and 2, Cu(OTf)2 for 3). Hence, the tetracoordinated bis-chloro complex 1 adopts a distorted square-planar geometry at solid state, whereas the pentacoordinated bis-aqua complex 3 displays an almost perfect square pyramidal conformation. Both complexes 1 and 3 react with H2O2 in acetonitrile, leading to the formation of copper(II)-hydroperoxo species according to the UV-Vis spectroscopic studies

Insights into the radical-radical and radical-substrate dimerization processes for substituted phenylmethylenepyrans

International audienceThe electrochemically-induced CC bond making/breaking for six differently R-substituted phenylmethylenepyrans has been investigated by voltammetry in organic media. All compounds display an irreversible oxidation peak whose potential is fully dependent on the electrophilic property of the substituent R. The electrochemical oxidation yields bis-pyrylium compounds by σ-σ CC bond formation. The initial methylenepyrans are recovered by cleavage of the CC bond through electrochemical reduction of the bis-pyrylium species. According to the voltammetric analysis, the mechanistic pathway, radical-radical or radical-substrate, for the intermolecular dimerization is fully R-dependent. Electronic structure calculations show that the spin population in the radical cation and the strength of the σ-σ CC bond in the dimer strongly depend on the nature of R. In addition, low-temperature electrochemical voltammetry (175 K), and room-temperature high scan rate cyclic voltammetry have been used to unravel the kinetics of the CC bond formation

Reversible redox switching of chromophoric phenylmethylenepyrans by carbon-carbon bond making/breaking

International audienceElectrochromic organic systems that can undergo substantial variation of their optical properties upon electron stimulus are of high interest for the development of functional materials. In particular, devices based on radical dimerization are appropriate because of the effectiveness and speed of the carbon-carbon bond making/breaking. Phenylmethylenepyrans are organic chromophores which are well suited for such purpose since their oxidation leads to the reversible formation of bispyrylium species by radical dimerization. In this paper, we show that the redox and spectroscopic properties of phenylmethylenepyrans can be modulated by adequate variation of the substituting group on the para position of the phenyl moiety, as supported by DFT calculations. This redox switching is reversible over several cycles and is accompanied by a significant modification of the UV-Vis spectrum of the chromophore, as shown by time-resolved spectroelectrochemistry in thin layer conditions

O-O bond cleavage by electrochemical reduction of a side-on peroxo dicopper model of hemocyanin.

International audienceThe redox properties of the μ-η2:η2 peroxo complex [Cu2(H6M4h)(O2)]2+ were elucidated. This study constitutes the first full electrochemical and spectroelectrochemical characterization of a side-on peroxo Cu2:O2 bioinorganic model complex. The peroxo complex is irreversibly reduced in a two- electron process localized on the peroxo ligand triggering the cleavage of the O-O bondLes propriétés redox du complexe peroxo μ-η2:η2 [Cu2(H6M4h)(O2)]2+, modèle de l’hémocyanine, ont été élucidées par des études électrochimiques et spectroélectrochimiques. La réduction du complexe peroxo est irréversible et s’effectue selon un processus à deux électrons localisé sur le ligand peroxyde, déclenchant la rupture de la liaison O-O

Incorporation of a platinum center in the pi-conjugated core of push-pull chromophores for nonlinear optics (NLO)

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Synthesis and properties of novel pyranylidene-based organic sensitizers for dye-sensitized solar cells

International audienceWe report herein the synthesis of nine new molecularly engineered metal-free organic pyranylidene-based dyes as efficient photosensitizers for Dye-Sensitized Solar Cells (DSSCs). Their photophysical, electrochemical, and photovoltaic properties were investigated, and their excited states have been modelled using Time-Dependent Density Functional Theory (TD-DFT). The investigation of the photovoltaic performances of this series of new dyes provided structure-property relationships where their Power Conversion Efficiencies (PCE) could be correlated to structural features, such as the length of the π-conjugated spacer and the nature of the substituents on the upper (positions 2 and 6) and lower parts (substituents on the exocyclic carbon) of the pyranylidene electron donor moiety. While these dyes fulfilled the criteria of efficient sensitizers for TiO2-based DSSCs, their photovoltaic performances were found to depend on the dye packing arrangements controlled by substituents on the pyranylidene group. The highest Power Conversion Efficiency of 5.52% was reached with the 20a dye containing phenyl substituent groups in both upper and lower parts of the pyranylidene fragment and with one thienyl π-conjugated spacer. © 2019 Elsevier Lt

Phosphorescent cyclometalated platinum( ii ) complexes with phenyldiazine N^C ligands

International audienceA series of phosphorescent platinum(II) complexes containing various phenyldiazine-type bidentate N^C ligands have been successfully synthesized and characterized. Structural modifications have been made to bidentate cyclometalating ligands regarding the nature of the diazine ring (pyrimidine, pyrazine and quinazoline), the substituent groups at the C4 position of the pyrimidine ring (OCH3, CF3) and the EDGs at the para position of the Pt atom (OCH3, Ph, NPh2, carbazol). In addition, the electronic properties of the azaheterocyclic ancillary ligand have been modulated in this series of complexes (pyridine, 4-methoxy-pyridine or pyrimidine). X-ray diffraction studies have been performed on three complexes, revealing Pt(II) ions in a distorted square-planar geometrical environment with no Pt(II)⋯Pt(II) interactions but with moderate π–π interactions in the solid-state structure. Electrochemical and computational studies suggest a ligand-centered reduction on the diazine ligands with, in some cases, additional contribution from the azaheterocyclic ancillary ligand, whereas oxidation occurs on the Pt-phenyl ring substituent moieties. All complexes exhibit phosphorescence emission ranging from green to red/near-infrared, both in solution and in the solid state. Complexes bearing a 2-(3-methoxyphenyl)pyrimidine ligand show the best PLQY of the series, up to 52% in a CH2Cl2 solution and 20% in the solid state. Furthermore, the solid state PLQY of one of the near-infrared emitting phenylquinazoline complex has been found to be 6%

Comparative studies of new pyranylidene-based sensitizers bearing single or double anchoring groups for dye-sensitized solar cells

International audienceMono- and di-anchoring γ-pyranylidene-based organic dyes featuring D–π–A and D–(π–A)2 architectures have been engineered as sensitizers for applications in Dye-Sensitized Solar Cells (DSSCs). Their photophysical, electrochemical and photovoltaic properties were further investigated. TD-DFT calculations were performed to rationalize the trends observed in the optical and electrochemical properties of the dyes. The investigation of the photovoltaic performances of this series of new dyes provided structure–property relationships where their Power Conversion Efficiencies (PCE) could be correlated to structural features, such as the length of the π-conjugated spacer, the nature of the substituents on the pyranylidene electron donor moiety and the number of anchoring groups. Dye-Sensitized Solar Cells based on mono-anchoring dyes were more efficient than the corresponding cells based on di-anchoring analogues due to high dye loading. The highest Power Conversion Efficiency of 5.23% was achieved with the mono-anchoring 17a dye containing t-butyl substituent groups on the pyranylidene fragment and with one thienyl π-conjugated spacer

Synthesis, photovoltaic performances and TD-DFT modeling of push-pull diacetylide platinum complexes in TiO2 based dye-sensitized solar cells.

International audienceIn this joint experimental-theoretical work, we present the synthesis and optical and electrochemical characterization of five new bis-acetylide platinum complex dyes end capped with diphenylpyranylidene moieties, as well as their performances in dye-sensitized solar cells (DSCs). Theoretical calculations relying on Time-Dependent Density Functional Theory (TD-DFT) and a range-separated hybrid show a very good match with experimental data and allow us to quantify the charge-transfer character of each compound. The photoconversion efficiency obtained reaches 4.7% for 8e (see TOC Graphic) with the tri-thiophene segment, which is among the highest efficiencies reported for platinum complexes in DSCs

Effect of Monoelectronic Oxidation of an Unsymmetrical Phenoxido-Hydroxido Bridged Dicopper(II) Complex

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