Guillaume Vives

Synthesis of Highly Fluorescent BODIPY-Based Nanocars

The convergent synthesis of inherently highly fluorescent nanocars incorporating 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY)-containing axles and p-carborane wheels is reported. These nanocars are expected to exhibit rolling motion with predetermined patterns over smooth surfaces, depending on their chassis. Their quantum yields of fluorescence (Phi(F) > 0.7) make them excellent candidates for imaging and tracking by single-molecule fluorescence microscopy. An analogue as a stationary control with tert-butyl groups instead of p-carborane wheels was also synthesized.

Micrometer-Scale Translation and Monitoring of Individual Nanocars on Glass

Nanomachines designed to exhibit controlled mechanical motions on the molecular scale present new possibilities of building novel functional materials. Single molecule fluorescence imaging of dye-labeled nanocars on a glass surface at room temperature showed a coupled translational and rotational motion of these nanoscale machines with an activation energy of 42 +/- 5 kJ/mol. The 3 nm-long dye-labeled carborane-wheeled nanocars moved by as much as 2.5 mum with an average speed of 4.1 nm/s. Translation of the nanocars due a wheel-like rolling mechanism is proposed and this is consistent with the absence of movement for a three-wheeled nanocar analogue and the stationary behavior of unbound dye molecules. These findings are an important first step toward the rational design and ultimate control of surface-operational molecular machines.

Synthesis of triester-functionalized molecular motors incorporating bis-acetylide trans-platinum insulating fragments

Bis-ferrocene compounds linked either by two triple bonds (1,4-di(ferrocenyl)butadiyne 1), or by the triple bond–platinum–triple bond sequence (trans-bis(ferrocenylethynyl)bis(triethylphosphine)platinum(II), 2) have been synthesized. The electronic coupling between the ferrocene groups has been estimated from the intensity of the intervalence transition in the electrochemically generated mixed valence complexes. Upon insertion of a platinum fragment a weak attenuation was observed, with the Vab parameter decreasing from 0.036 eV for 1 to 0.025 eV for 2. A theoretical study has also been performed, using a combination of DFT for geometry optimization and Extended Huckel Theory for the estimation of the electronic coupling. It was found that the electronic coupling decreases from 0.090 eV for 1 to 0.022 eV for a model of 2. In a second part of this work, we describe the synthesis of two molecular motors incorporating the ligand hydrotris[6-(ethoxycarbonyl)indazol-1-yl]borate which exhibits three pendant ester groups dedicated to be anchored onto an oxide surface. This stator is connected through a ruthenium centre to a pentasubstituted cyclopentadienyl rotor bearing ferrocene terminal electroactive groups, linked either by a phenylethynyl spacer (complex 4) or a spacer containing bis-acetylide trans-platinum insulating fragments (complex 8).

Molecular machinery: synthesis of a "nanodragster".

The synthesis and imaging by scanning tunneling microscopy of a mixed wheeled nanovehicle composed of a p-carborane small-wheeled short front axle and a C(60) large-wheeled long rear axle that has been termed a nanodragster due to the structural relation to a dragster are reported. This nanodragster is expected to exhibit motion at a lower temperature than pure C(60)-wheeled nanocars and should allow the investigation of the role played by p-carborane wheels in directional motion.

Toward chemical propulsion: synthesis of ROMP-propelled nanocars.

The synthesis and ring-opening metathesis polymerization (ROMP) activity of two nanocars functionalized with an olefin metathesis catalyst is reported. The nanocars were attached to a Hoveyda-Grubbs first- or second-generation metathesis catalyst via a benzylidene moiety. The catalytic activity of these nanocars toward ROMP of 1,5-cyclooctadiene was similar to that of their parent catalysts. The activity of the Hoveyda-Grubbs first-generation catalyst-functionalized nanocar was further tested with polymerization of norbornene. Hence, the prospect is heightened for a ROMP process to propel nanocars across a surface by providing the translational force.

Fullerene/Thiol-Terminated Molecules

A series of fullerene-terminated oligo(phenylene ethynylene) (OPEs) have been synthesized for potential use in electronic or optoelectronic device monolayers. Electronic properties such as the energy levels and the distribution of HOMOs and LUMOs of fullerene-terminated OPEs have been calculated using the ab initio method at the B3LYP/6-31G(d) level. The calculations have revealed the concentration of frontier orbitals on the fullerene cage and a narrow distribution of HOMO-LUMO energy gaps. Ultraviolet photoelectron spectroscopy and inverse photoemission spectroscopy studies have been performed to further examine the electronic properties of the fullerene-terminated OPEs on gold surfaces. The obtained broad photoelectron spectra suggest that there are strong intermolecular interactions in the fullerene self-assembled monolayers, and the small bandgap (approximately 1.5 eV), determined by the photoelectron spectroscopy, indicates the unique nature of the fullerene-terminated OPEs in which the C(60) moiety can be connected to the Au surface through the conjugated OPE backbone.

Dynamics of ion-regulated photoinduced electron transfer in BODIPY-BAPTA conjugates

Efficient Ca(2+)-switched fluorescent sensors, where fluorescence output is governed by a light-activated ion-gated electron transfer pathway, can be obtained on combining BODIPY chromophores with a readily oxidized biocompatible and selective BAPTA receptor. Herein we report the synthesis and studies of two such conjugates, which vary in the nature of the spacer separating the two electroactive components, namely none (1) or phenyl (2). Single crystal X-ray crystallography and molecular modelling structures and calculations give information on molecular and electronic structure, while steady-state fluorescence experiments show high Ca(2+)-induced fluorescence enhancement factors of 122 and 23 and K(d) values of 0.50 μM and 0.13 μM for 1 and 2, respectively. Notably, studies of the ultrafast photoinduced processes (through transient absorption spectroscopy) give access to electron transfer dynamics in pseudo-physiological media as well as in a polar non-protic solvent and information about the fate of the excited molecules in the presence and absence of calcium. In water, electron transfer rates as high as 3.3 × 10(12) s(−1) and 8.3 × 10(11) s(−1) are measured for the ion-free, directly connected conjugate and the variant incorporating a phenyl spacer, respectively. This electron transfer pathway is efficiently blocked by the presence of an ion, restoring fluorescence.

Synthesis of Fluorescent Dye-Tagged Nanomachines for Single-Molecule Fluorescence Spectroscopy

In an effort to elucidate the mechanism of movement of nanovehicles on nonconducting surfaces, the synthesis and optical properties of five fluorescently tagged nanocars are reported. The nanocars were specifically designed for studies by single-molecule fluorescence spectroscopy and bear a tetramethylrhodamine isothiocyanate fluorescent tag for excitation at 532 nm. The molecules were designed such that the arrangement of their molecular axles and p-carborane wheels relative to the chassis would be conducive to the control of directionality in the motion of these nanovehicles.

A star-shaped ruthenium complex with five ferrocenyl-terminated arms bridged by trans-platinum fragments

We present the synthesis of the new heteropolytopic penta(4-ethynylphenyl)cyclopentadiene ligand, its complexation through the Cp ring to ruthenium tris(indazolyl)borate and through the terminal alkyne groups to five ferrocenyl ethynyl platinum units, yielding an undecanuclear heterotrimetallic complex.

Cyclodextrin Polyrotaxanes as a Highly Modular Platform for the Development of Imaging Agents

Selectively functionalized cyclodextrins with a bodipy fluorescent tag or Gd(3+) complex were synthetized and threaded onto a polyammonium chain to form polyrotaxanes. This modular supramolecular assembly makes an ideal platform for bimodal (fluorescent and MRI) imaging applications.