Yannick Rio

A fullerene core to probe dendritic shielding effects

Abstract Dendrimers with a C 60 core have been obtained by cyclization of dendritic bis-malonate derivatives at the carbon sphere. The resulting bis-methanofullerene derivatives have been characterised by electrospray (ES) and/or MALDI-TOF mass spectrometries. UV–VIS absorption spectra, fluorescence spectra, and fullerene singlet excited state lifetimes have been determined in solvents of different polarity (toluene, dichloromethane, acetonitrile). These data suggest a tighter core/periphery contact upon increase of solvent polarity and dendrimer size. In all the investigated solvents, the fullerene triplet lifetimes are steadily increased with the dendrimer volume, reflecting lower diffusion rates of O 2 inside the dendrimers along the series. Measurements of quantum yields of singlet oxygen sensitization indicate that longer lived triplet states generate lower amounts of singlet oxygen ( 1 O 2 ∗ ) in dichloromethane but not in apolar toluene suggesting a tighter contact between the dendritic branches and the fullerene core in CH 2 Cl 2 . In acetonitrile, the trend in singlet oxygen production is peculiar. Effectively, enhanced singlet oxygen production is monitored for the largest dendrimer. This reflects specific interactions of excited 1 O 2 ∗ molecules with the dendritic wedges, as probed by singlet oxygen lifetime measurements, possibly as a consequence of trapping effects.

Water soluble supramolecular cyclotriveratrylene-[60]fullerene complexes with potential for biological applications

Abstract Polybenzyl ether dendritic branches with peripheral triethyleneglycol chains have been attached to a cyclotriveratrylene core and the supramolecular complexes obtained from the resulting macrocyclic derivatives and C 60 were found to be water soluble.

Fullerodendrimers with peripheral triethyleneglycol chains: synthesis, mass spectrometric characterization, and photophysical properties

Poly(aryl ether) dendritic branches terminated with peripheral triethyleneglycol chains have been attached to C60. The resulting fullerodendrimers have been characterised by electrospray mass spectrometry (ESMS), which appears to be a particularly interesting analytical tool for the unambiguous structural assignment of such high molecular weight fullerene derivatives. Their photophysical properties have been systematically investigated in three solvents, namely toluene, dichloromethane, and acetonitrile. The changes observed in the photophysical properties along the series suggest an increasing interaction between the poly(aryl ether) dendritic wedges and the fullerene core, which brings about an increasing isolation of the central chromophore from the exterior. Finally, thanks to their high solubility, fullerodendrimers 1–4 have been easily incorporated in mesoporous silica glasses and preliminary measurements on the resulting doped samples have revealed efficient optical limiting properties.

Fullerodendrimers with peripheral triethyleneglycol chains

Abstract Triethylene glycol terminated poly(aryl ether) dendritic branches with an aldehyde function at the focal point have been prepared and attached to C60 by a 1,3-dipolar cycloaddition.

Electronic properties of oligophenylenevinylene and oligophenyleneethynylene arrays constructed on the upper rim of a calix[4]arene core

Heck and Sonogashira cross-coupling reactions have been used for the functionalization of the upper rim of a tetraiodinated calix[4]arene. In this way, oligophenylenevinylene (OPV) and oligophenyleneethynylene (OPE) arrays have been constructed on the calix[4]arene core to produce covalent assemblies of four π-conjugated chromophores. Electrochemical properties have been investigated by cyclic voltammetry in different solvent/electrolyte systems. Both OPV and OPE calixarenes show the simultaneous reduction of three out of four units, followed, at more negative potential, by the reduction of the fourth unit. This behaviour can be rationalized in view of a partial deconjugation in one OPV or OPE unit. On the other hand, these calixarenes show only oxidation processes corresponding to the exchange of one electron, thus demonstrating the lack of electrochemical equivalency of the OPV or OPE units, in contrast to the reduction behaviour. Electronic absorption and emission spectra have been recorded in solvents of different polarity (toluene, dichloromethane, and benzonitrile). The absorption spectra of the OPV calixarene do not match to the sum of the component units as a consequence of the partial deconjugation of the OPV arms in the calixarene structure. On the contrary, fluorescence spectra, quantum yields and excited state lifetimes of the OPV calixarene are nearly identical to those of the corresponding model compound. The trend of the absorption and emission spectra for the OPE calixarene is reversed relative to that of the OPV counterpart. Absorption spectra are well-matched with those of four trimeric OPE fragments but emission spectra exhibit, besides the typical OPE monomeric fluorescence, a broader and longer-lived emission feature on the low-energy spectral side, attributable to excimer-type interactions. Therefore the arrangement of OPV or OPE units within the same calix-4-arene skeleton brings about different effects on the electronic and luminescence properties of the multicomponent system.

Fullerohelicates: a new class of fullerene-containing supermoleculesElectronic supplementary information (ESI) available: 1H-NMR spectra of 1 and Cu2(1)2. See http://www.rsc.org/suppdata/cc/b4/b404742g/

A multicomponent array made of a bis-copper(I) helicate core and two peripheral fullerene subunits has been prepared and electron transfer from the photoexcited Cu(I)-complexed unit to C60 occurs.

Synthesis and electronic properties of fullerene derivatives substituted with oligophenylenevinylen–ferrocene conjugates

C60-bridge-Fc arrays (C60-Fc, C60-PV-Fc, C60-2PV-Fc, C60-3PV-Fc), bearing a fulleropyrrolidine and a ferrocene (Fc) unit connected via an oligophenylenevinylene (OPV) bridge have been prepared. Suitable dyads (PV-Fc, 2PV-Fc, 3PV-Fc) to be used as references for the study of the electronic properties of the largest arrays have been also synthesized. The electrochemical properties of all the dyad and triad multicomponent arrays have been studied by cyclic voltammetry, evidencing a rich and complex electrochemical pattern due to the presence of several electroactive moieties. The first reduction is always assigned to the fullerene moiety and the first oxidation is centred on the Fc group, making the triad systems suitable candidates for photoinduced electron transfer via the interposed bridge. Photophysical studies evidence a complete quenching of the fluorescence of organic conjugated moieties in PV-Fc, 2PV-Fc, 3PV-Fc, possibly via energy transfer to the Fc unit. In the more complex C60/Fc arrays the quenching of the C60 moieties is ultrafast in CH2Cl2 solution and most likely attributable to electron transfer via the OPV wire. In toluene, the dynamic process of singlet and triplet fullerene quenching can be traced via time resolved fluorescence and transient absorption spectroscopy and the values of the rate constants are smaller with increasing donor–acceptor distance. Definitive assignment of the intercomponent quenching mechanism between the fullerene and the ferrocene moiety (energy or electron transfer) can hardly be obtained. Several repeated attempts to detect the radical anion fingerprint of fulleropyrrolidine with transient absorption failed, even in bimolecular quenching experiments. This supports the view that distance-dependent C60 → Fc singlet–triplet and triplet–triplet energy transfer may compete successfully with the desired charge separation step.

Thin layer cyclic voltammetry: an efficient tool to determine the redox characteristics of large dendrimers

Dendrimers with an electroactive bis(phenanthroline) copper(I) core have been prepared and thin layer cyclic voltammetry (TLCV) found to be an efficient tool to determine their redox characteristics in spite of the slow electron transfer kinetics observed for the largest compounds.

NANO-ENCAPSULATION OF FULLERENE IN DENDRIMERS

Two series of dendrimers with peripheral triethyleneglycol chains and a fullerene core have been prepared and characterized. The photophysical properties have been investigated in different solvents (toluene, dichloromethane and acetonitrile). In particular, we have shown that the fullerene triplet lifetimes are steadily increased with the dendrimer volume in all the investigated solvents. Interestingly, the triplet lifetimes of the largest fullerodendrimer in the three solvents lead towards a similar value suggesting that the fullerene core is in a similar environment whatever the nature of the solvent is. In other words the C60 unit is, to a large extent, not surrounded by solvent molecules but substantially buried in the middle of the dendritic structure, which is capable of creating a specific site-isolated nanoenvironment around the fullerene moiety.