Cédric R. Mayer

Hybrid organic-inorganic polyoxometalate compounds: from structural diversity to applications.

Polyoxometalates (POMs) are discrete anionic metaloxygen clusters which can be regarded as soluble oxide fragments. They exhibit a great diversity of sizes, nuclearities, and shapes. They are built from the connection of {MOx} polyhedra, M being a d-block element in high oxidation state, usually VIV,V, MoVI, or WVI.1 While these species have been known for almost two centuries, they still attract much interest partly based on their large domains of applications. They play a great role in various areas ranging from catalysis,2 medicine,3 electrochemistry,4 photochromism,5 to magnetism.6 This palette of applications is intrinsically due to the combination of their added value properties (redox properties, large sizes, high negative charges, nucleophilicity...). Parallel to this domain, the organic-inorganic hybrids area has followed a similar expansion during the last 10 years. The concept of organic-inorganic hybrid materials * To whom correspondence should be addressed. E-mail: dolbecq@ chimie.uvsq.fr. Chem. Rev. 2010, 110, 6009–6048 6009

Gold nanoparticles functionalized with gadolinium chelates as high-relaxivity MRI contrast agents.

Water-dispersible gold nanoparticles functionalized with paramagnetic gadolinium have been fully characterized, and the NMRD profiles show very high relaxivities up to 1.5 T. Characterization using TEM images and dynamic light scattering indicate a particle size distribution from 2 to 15 nm. The gold cores of the nanoparticles do not contribute significantly to the overall magnetic moment.

Coupled Sensitizer-Catalyst Dyads: Electron-Transfer Reactions in a Perylene-Polyoxometalate Conjugate

Ultrafast discharge of a single-electron capacitor: A variety of intramolecular electron-transfer reactions are apparent for polyoxometalates functionalized with covalently attached perylene monoimide chromophores, but these are restricted to single-electron events. (et=electron transfer, cr=charge recombination, csr=charge-shift reaction, PER=perylene, POM=polyoxometalate).A new strategy is introduced that permits covalent attachment of an organic chromophore to a polyoxometalate (POM) cluster. Two examples are reported that differ according to the nature of the anchoring group and the flexibility of the linker. Both POMs are functionalized with perylene monoimide units, which function as photon collectors and form a relatively long-lived charge-transfer state under illumination. They are reduced to a stable pi-radical anion by electrolysis or to a protonated dianion under photolysis in the presence of aqueous triethanolamine. The presence of the POM opens up an intramolecular electron-transfer route by which the charge-transfer state reduces the POM. The rate of this process depends on the molecular conformation and appears to involve through-space interactions. Prior reduction of the POM leads to efficient fluorescence quenching, again due to intramolecular electron transfer. In most cases, it is difficult to resolve the electron-transfer products because of relatively fast reverse charge shift that occurs within a closed conformer. Although the POM can store multiple electrons, it has not proved possible to use these systems as molecular-scale capacitors because of efficient electron transfer from the one-electron-reduced POM to the excited singlet state of the perylene monoimide.

A porphyrin-polyoxometallate bio-inspired mimic for artificial photosynthesis

A multi-porphyrin cluster has been covalently attached to a polyoxometallate (POM) catalyst so as to form an advanced model for the photosynthetic reaction complex. This bio-inspired mimic displays efficient energy transfer from the peripheral zinc porphyrins (ZnP) to the central free-base porphyrin (FbP). The latter species participates in a light-induced electron transfer with the POM. Charge recombination is hindered by hole transfer from the FbP to one of the ZnPs. Charge accumulation occurs at the POM under illumination in the presence of a sacrificial electron donor.

Polypyridyl ruthenium complexes as coating agent for the formation of gold and silver nanocomposites in different media. Preliminary luminescence and electrochemical studies

Three polypyridyl ruthenium complexes, [(phen)2Ru(2,2′-p-phenylene-bis(imidazo[4,5-f][1,10])phenanthroline)](X)2 (1·X2), [(phen)2Ru((4-pyridine)oxazo[4,5-f][1,10]phenanthroline)](X)2 (2·X2) and [(phen)2Ru((3-thiophene)imidazo[4,5-f][1,10]phenanthroline)](X)2 (3·X2), X− = PF6− or Cl−, have been used to functionalize and stabilize gold and silver nanoparticles in aqueous and non aqueous (acetonitrile) media. Direct interaction between the metallic nanoparticles and the ruthenium complexes was ensured by bidentate chelating phenanthroline (1), monodentate pyridine (2) or monodentate thiophene (3) groups. The influence of several parameters was studied in order to control the size, shape and stability of the nanocomposites thus formed: the nature of the metallic nanoparticles, the nature of the coating ruthenium complex, the ratio R = [Mn+]/[Ru2+] (M = Ag or Au) and the solvent. The colloidal solutions have been characterized by UV-Vis spectroscopy, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Preliminary electrochemical and luminescence measurements have shown the influence of the metallic nanoparticle on the properties of the ruthenium complexes.

Size controlled formation of silver nanoparticles by direct bonding of ruthenium complexes bearing a terminal mono- or bi-pyridyl group

Two polypyridyl ruthenium complexes containing either a terminal pyridine or phenanthroline group have been used to coat silver nanoparticles and control their size depending on the Ag/[RuII] ratio.

Electrochemical, linear optical, and nonlinear optical properties and interpretation by density functional theory calculations of (4-N,N-dimethylaminostyryl)-pyridinium pendant group associated with polypyridinic ligands and respective multifunctional metal complexes (Ru(II) or Zn(II)).

The synthesis, linear optical and nonlinear optical properties, as well as the electrochemical behavior of a series of pro-ligands containing the 4-(4-N,N-dimethylaminostyryl)-1-methyl pyridinium (DASP(+)) group as a push-pull moiety covalently linked to terpyridine or bipyridine as chelating ligands are reported in this full paper. The corresponding multifunctional Ru(II) and Zn(II) complexes were prepared and investigated. The structural, electronic, and optical properties of the pro-ligands and the ruthenium complexes were investigated using density functional theory (DFT) and time-dependent (TD) DFT calculations. A fairly good agreement was observed between the experimental and the calculated electronic spectra of the pro-ligands and their corresponding ruthenium complexes. A quenching of luminescence was evidenced in all ruthenium complexes compared with the free pro-ligands but even the terpyridine-functionalized metal complexes exhibited detectable luminescence at room temperature. Second order nonlinear optical (NLO) measurements were performed by Harmonic Light Scattering and the contribution of the DASP(+) moieties (and their relative ordering) and the metal-polypyridyl core need to be considered to explain the nonlinear optical properties of the metal complexes.

1,10-Phenanthroline and 1,10-phenanthroline-terminated ruthenium(II) complex as efficient capping agents to stabilize gold nanoparticles: Application for reversible aqueous–organic phase transfer processes

1,10-Phenanthroline (phen) and 1,10-phenanthroline-terminated ruthenium(II) complex [Ru-Lphen](2+) have been used to stabilize and functionalize gold nanoparticles (Au-NPs). The strong interaction between the nitrogen atoms of phen and the surface of Au-NPs allowed for the phase transfer of Au-NPs from toluene to aqueous phase containing [Ru-Lphen](2+). Reverse phase transfer of these Au-NPs from water to acetonitrile by substituting the Cl(-) counter anion by PF(-)(6) has also been demonstrated. Such facile post-functionalization, phase transfer and solvent transfer processes using metallic complexes bearing a terminal phenanthroline pendant group constitute a prerequisite for further studies of the electronic and optical properties of these NCs in various media.

A multicolor photoinitiator for cationic polymerization and interpenetrated polymer network synthesis: 2,7-di-tert-butyldimethyldihydropyrene.

For polymer synthesis upon visible light, actual photoinitiator operates in a restricted part of the spectrum. As a consequence, several photoinitiators are necessary to harvest all of the emitted visible photons. Herein, 2,7-di-tert-butyldimethyldihydropyrene is used for the first time as a multicolor photoinitiator for the cationic polymerization of epoxides. Upon addition of diphenyliodonium hexafluorophosphate and optionally N-vinylcarbazole, the originality of this approach is to allow efficient monomer conversions under various excitation light sources in the 360-650 nm wavelength range: halogen lamps, and light-emitting and laser diodes. The synthesis of an interpenetrated polymer network from an epoxide/acrylate blend using a red light at 635 nm is also feasible. The formed polymer material exhibits a photochromic character.

Tunable Optical Properties of Chromophores Derived from Oligo(p-phenylene vinylene)

A series of 11 symmetric push-pull chromophores consisting of electron-accepting groups connected through a central pi-conjugated system derived from oligo(p-phenylene vinylene) (OPV) were designed and synthesized. Electronic and spectroscopic properties were investigated by UV-visible absorption, fluorescence spectroscopy, and cyclic voltammetry. By finely tuning the electron-withdrawing ability of the acceptors as well as the length of the pi-conjugated spacer, a wide range of dyes exhibiting strong absorption and emission were obtained.