Béatrice Delavaux-Nicot

Electrophosphorescent homo- and heteroleptic copper(I) complexes prepared from various bis-phosphine ligands

Homo- and heteroleptic copper(I) complexes obtained from various chelating bis-phosphine ligands and Cu(CH3CN)4BF4 have been used for the preparation of light emitting devices.

Dendrimers : towards catalytic, material and biomedical uses

This book will be mainly focussed on the properties and uses of dendrimers and dendrons. The aim of this book is to be the reference book about dendrimers applications. It will not describe all details, but it will give the reader a unique overview of what has currently been done with dendrimers, with numerous references and illustrations. It will be divided in four main parts: Part 1) Generalities, syntheses, characterizations and properties; Part 2) Applications in catalysis; Part 3) Applications for the elaboration or modification of materials; and Part 4) Applications in biology/medicine. The role of the nanometric size and the multiple functions of dendrimers on the properties will be emphasized.

“Janus” dendrimers: syntheses and properties

“Janus” dendrimers, i.e.dendrimers constituted of two dendrimeric wedges and terminated by two different functionalities, are reviewed. Both the synthetic aspects and the particular properties afforded by the presence of two different functions in two precise areas of the surface of the Janus dendrimers are reported. This review is organized depending on the type of internal structure (benzyl ether, phenylene, phosphorus, PAMAM, DAB, lysine, alkyl ether, ester, amide, etc.).

Photoinduced electron transfer in a clicked fullerene–porphyrin conjugate

A stable C60 derivative bearing an azide functional group has been prepared and used as a building block for the preparation of a fullerene–porphyrin conjugate (F–P–F) by reaction with a Zn(II)–porphyrin bearing two terminal alkyne groups under the copper mediated Huisgen 1,3-dipolar cycloaddition conditions. The electrochemical and photophysical properties of the resulting multicomponent system have been investigated in detail. In benzonitrile, F–P–F undergoes photoinduced electron transfer and the resulting charge separated state is relatively long lived (τ = 0.48 µs). In contrast, intramolecular energy transfer has been evidenced in toluene, with the generation of the fullerene triplet level upon selective excitation of the porphyrin moiety. In this solvent, a CT emission band is observed in the near-infrared region (λmax = 940 nm) as a consequence of a conformational equilibrium causing, to a minor extent, the formation of intramolecular porphyrin–fullerene tight pairs. This finding is supported by measurements of singlet oxygen sensitization and quenching of the long-lived fullerene centered triplet state in the oxygen free solution.

Anionic triscyclopentadienyluranium(III) hydrides

Abstract Addition of H − to [(C 5 H 4 R) 3 U] (R  H, Me, SiMe 3 , or t Bu) or sodium amalgam reduction of the U IV hydrides [(C 5 H 4 R) 3 UH] (R  SiMe 3 , or t Bu) afforded the hydrido-bridged anions [(C 5 H 4 R) 3 UHU(C 5 H 4 R) 3 ] − (R  H or Me) or the monomeric anions [(C 5 H 4 R) 3 UH] − (R  SiMe 3 or t Bu). Crystals of [Na(18-crown-6)(THF) 2 ][(C 5 H 4 SiMe 3 ) 3 UHU(C 5 H 4 SiMe 3 ) 3 ] were obtained from an equimolar mixture of [Na(18-crown-6)][(C 5 H 4 SiMe 3 ) 3 UH] and [(C 5 H 4 SiMe 3 ) 3 U] and their structure determined.

Fullerodendrimers with a perylenediimide core

Dendritic C60–perylenediimide (PDI) conjugates PerG1–PerG3 have been prepared under esterification conditions starting from a perylene diol building block (Per) and fullerodendrons bearing a carboxylic acid function at the focal point. The cyclic voltammograms recorded for PerG1–PerG3 show the characteristic electrochemical features of both constitutive units, i.e.methanofullerene and PDI. The comparison with the corresponding model compounds (Per and F) shows that the oxidation of the dendrimers is centered on the PDI core, while the first reduction corresponds to a fullerene-centred process. The photophysical properties of PerG1–PerG3 and of the related reference systems Per and F were investigated in toluene solution. Per and F exhibit almost superimposed fluorescence bands sitting across the Vis and NIR spectral regions, showing that the corresponding singlet states are virtually isoenergetic (∼1.75 eV). The two bands are characterized by very different fluorescence quantum yields and short singlet lifetimes; Per: Φfluo = 7.8%, τ = 3.7 ns; F: Φfluo = 0.04%, τ = 1.8 ns. In the dendrimers, the isoenergetic singlet levels of the PDI and fullerene moieties lead to a very peculiar luminescence behaviour that is invariably found regardless of the excitation wavelength. The detected fluorescence band in PerG1–PerG3 has always the shape of the PDI central core, reduced in intensity by about 20 times compared to Per, whilst the lifetime is that of the peripheral fullerene unit. At 298 K, this unconventional behaviour is interpreted by a kinetic model involving fast equilibration of the singlet levels separated by about 0.06 eV, the PDI-centred level being the highest one. At 77 K the equilibration is suppressed and the fluorescence of the PDI central core is fully restored, showing that the corresponding level becomes lower-lying than the fullerene singlet. Bimolecular transient absorption studies made on solutions containing F and Per show that triplet energy transfer from the photoexcited fullerene to the PDI occurs. Similar investigations on PerG1–PerG3 only exhibit the features of the PDI triplet, evidencing that this level is populated in a timescale shorter than 10 ns and is the final sink of the above lying excited states. Therefore, in dendrimers PerG1–PerG3, the photophysical behaviour is not dependent on the dendrimer size and structure, and light excitation is followed by inbound energy transfer to the central core and generation of the PDI triplet state.

Metal-atom impact on the self-assembly of cup-and-ball metalloporphyrin-fullerene conjugates.

A fullerene ammonium derivative has been combined with different metalloporphyrin-crown ether receptors to generate very stable supramolecules. The combination of fullerene-porphyrin and ammonium-crown ether interactions leads to a strong chelate effect as evidenced by a high effective molarity (3.16 M). The different parameters influencing the stability of the supramolecular ensembles, in particular the nature of the metal in the porphyrin moiety, have been rationalized with the help of theoretical calculations thus providing new insights into fullerene-porphyrin interactions.

MONO- AND 1,1'-DISUBSTITUTED AZA FERROCENYL COMPOUNDS : EVIDENCE FOR AN ORIGINAL ELECTROACTIVE FLUORESCENT SPECIES

New azaalkyl or azacrown ferrocenyl compounds containing a C5H4COCC- linkage are accessible from mono- or diacetylferrocene upon treatment with the appropriate aldehydes (CHOC6H4-p-R, R = NEt2, N-aza-15-crown-5). Preliminary results concerning the electrochemical behaviour of complexes [(C5H5)Fe(C5H4COCH=CHC6H4NEt2)] (3a), [Fe(C5H4COCH=CHC6H4NEt2)2] (5a), the novel ferrocenophane [Fe(C5H4COCH2)2CHC6H4NEt2] (6a) and its protonated species [Fe(C5H4COCH2)2CHC6H4NHEt2][BF4] (7a), are reported. The ferrocenyl ligand 5a is a rare example of a molecule which is both electroactive and fluorescent.

Conjugated Porphyrin Dimers: Cooperative Effects and Electronic Communication in Supramolecular Ensembles with C60

Two new conjugated porphyrin-based systems (dimers 3 and 4) endowed with suitable crown ethers have been synthesized as receptors for a fullerene-ammonium salt derivative (1). Association constants in solution have been determined by UV–vis titration experiments in CH2Cl2 at room temperature. The designed hosts are able to associate up to two fullerene-based guest molecules and present association constants as high as ∼5 × 108 M–1. Calculation of the allosteric cooperative factor α for supramolecular complexes [3·12] and [4·12] showed a negative cooperative effect in both cases. The interactions accounting for the formation of the associates are based, first, on the complementary ammonium-crown ether interaction and, second, on the π–π interactions between the porphyrin rings and the C60 moieties. Theoretical calculations have evidenced a significant decrease of the electron density in the porphyrin dimers 3 and 4 upon complexation of the first C60 molecule, in good agreement with the negative cooperativity found in these systems. This negative effect is partially compensated by the stabilizing C60–C60 interactions that take place in the more stable syn-disposition of [4·12].

Fullerene Derivatives Functionalized with Diethylamino-Substituted Conjugated Oligomers: Synthesis and Photoinduced Electron Transfer

Diethylamino-substituted oligophenylenevinylene (OPV) building blocks have been prepared and used for the synthesis of two [60]fullerene-OPV dyads, F-D1 and F-D2, which exhibit different conjugation length of the OPV fragments. The electrochemical properties of these acceptor-donor dyads have been studied by cyclic voltammetry. The first reduction is always assigned to the fullerene moiety and the first oxidation centered on the diethylaniline groups of the OPV rods, thus making these systems suitable candidates for photoinduced electron transfer. Both the OPV and the fullerene-centered fluorescence bands are quenched in toluene and benzonitrile, which suggests the occurrence of photoinduced electron transfer from the amino-substituted OPVs to the carbon sphere in the dyads in both solvents. By means of bimolecular quenching experiments, transient absorption spectral fingerprints of the radical cationic species are detected in the visible (670 nm) and near-IR (1300-1500 nm) regions, along with the much weaker fullerene anion band at lambda(max)=1030 nm. Definitive evidence for photoinduced electron transfer in F-D1 and F-D2 comes from transient absorption measurements. A charge-separated state is formed within 100 ps and decays in less than 5 ns.