Guy Royal

Charge Transport in Photoswitchable Dimethyldihydropyrene-Type Single-Molecule Junctions

The conductance properties of a photoswitchable dimethyldihydropyrene (DHP) derivative have been investigated for the first time in single-molecule junctions using the mechanically controllable break junction technique. We demonstrate that the reversible structure changes induced by isomerization of a single bispyridine-substituted DHP molecule are correlated with a large drop of the conductance value. We found a very high ON/OFF ratio (>10(4)) and an excellent reversibility of conductance switching.

Complexation and electrochemical sensing of anions by amide-substituted ferrocenyl ligands

New amide-containing ferrocenyl ligands, L1–5, were prepared and the voltammetric and 1H NMR investigations of anion binding were carried out in organic media. The electrochemical recognition ability of L1–5 towards F−, HSO4−, H2PO4− and ATP2− is based on the synergy between H-bonding to amide protons in anion complexation to reduced, neutral ligands and ion-pairing interactions developed with the oxidized, cationic form of the ligands. The strength of the anion–ligand interactions depends on the number of ferrocene centers and amide groups in the receptor, and on the accessibility of the binding sites. Clear two-wave cyclic voltammetry features allowed the amperometric titration of H2PO4− and ATP2− by ligands L4 and L5 built from a cyclotriveratrylene structural unit, and containing a combination of three ferrocene centers with three (L4) or six (L5) amide groups.

(Ferrocenylmethyl)trimethylammonium cation: a very simple probe for the electro-chemical sensing of dihydrogen phosphate and ATP anionsElectronic supplementary information (ESI) available: cyclic voltammograms of 1 in the presence of increasing amounts of ATP2– or HSO4–. See http://www.rsc.org/suppdata/nj/b1/b107713a/

By virtue of strong ion-pairing interactions that are reinforced following its oxidation to the ferrocinium form, (ferrocenylmethyl)trimethylammonium cation is able to electrochemically sense dihydrogen phosphate and ATP anions in organic electrolytes; clear two-wave voltammetry features allow their amperometric titration by this very simple derivative of ferrocene.

Soluble heterometallic coordination polymers based on a bis-terpyridine-functionalized dioxocyclam ligand.

Soluble homo- and heterometallic coordination polymers containing transition metal cations (Cu(2+), Fe(2+), Co(2+), and Ni(2+) ions) were prepared in a two-step procedure using a polytopic bis(terpyridine)dioxocyclam ligand 1H(2) (dioxocyclam = 1,4,8,11-tetraazacyclotetradecane-5,7-dione). These supramolecular systems incorporate two different metal complexes, the metal cations being located both between two terpyridine units and in the macrocyclic framework. The characterization of these soluble architectures was investigated by cyclic voltammetry, mass spectrometry, viscosimetry, and UV-vis absorption and electron paramagnetic resonance (EPR) spectroscopies. Our results clearly indicate the formation of well-organized heterometallic polymers in which two different metal ions alternate in the self-assembled structure. These investigations furthermore brought to light an original acid-controlled disassembling process of the homometallic copper(II) polymer into dinuclear complexes.

Anion recognition and redox sensing by a metalloporphyrin–ferrocene–alkylammonium conjugate

The synthesis and characterization of a novel redox molecular receptor is reported. This chemosensor is structured on a ferrocene fragment whose cyclopentadienyl moieties have been connected to distinct and complementary zinc porphyrin and alkylammonium binding sites, enabling multipoint recognition and detection of anionic species. Cumulative effects of multiple anchoring points on this ammonium–ferrocene–metalloporphyrin chemosensor allowed the unprecedented ferrocene-based voltammetric sensing of halide anions.

Coordination of Ferrocenyl Ligands Bearing bipy Subunits: Electrochemical, Structural and Spectroscopic Studies

The coordinative properties of mono(bipy) and bis(bipy) (bipy refers to 6or 6,6 -substituted 2,2 -bipyridine) carbonyloxyand carboxamido-bridged derivatives of ferrocene L1−5 towards a number of metal cations (CuI, CuII, NiII, FeII, CoII, HgII, PbII, AgI) have been investigated by the interplay of voltammetry, mass spectrometry and X-ray diffraction studies. Particular attention was paid to the electrochemical recognition properties of these redox-active ligands, as monitored by modulation of the ferrocene/ferricinium redox couple upon complexation. It was found that the bis(bipy)bridged ligands exhibit a sandwich effect that gives rise to a

From molecular copper complexes to composite electrocatalytic materials for selective reduction of CO2 to formic acid

The development of new energy storage technologies is central to solving the challenges facing the widespread use of renewable energies. An option is the reduction of carbon dioxide (CO2) into carbon-based products which can be achieved within an electrochemical cell. Future developments of such processes depend on the availability of cheap and selective catalysts at the electrode. Here we show that a unique well-characterized active electrode material can be simply prepared via electrodeposition from a molecular copper complex precursor. The best performances, namely activity (150 mV onset overpotential and 1 mA cm−2 current density at 540 mV overpotential), selectivity (90% faradaic yield) and stability for electrocatalytic reduction of CO2 into formic acid in DMF/H2O (97 : 3 v/v) have been obtained with the [Cu(cyclam)](ClO4)2 complex (cyclam = 1,4,8,11-tetraazacyclotetradecane) as the precursor. Remarkably the organic ligand of the Cu precursor remains part of the composite material and the electrocatalytic activity is greatly dependent on the nature of that organic component.

Redox sensing of anions in pure aqueous environment by ferrocene-containing 4,4′-bipyridinium-based receptors and polymer films

Selective voltammetric sensing of ATP(2-) anions in water was achieved using ferrocene-viologen based redox active receptors and related polymer films.

Characterization of strain recovery and “self-healing” in a self-assembled metallo-gel

We report a self-assembled metallo suprapolymer gel exhibiting remarkable self-healing features. The Ni2BTC metallo suprapolymer gels result from the complexation of Ni(2+) metal ions by a tritopic ligand (bis-terpyridine cyclam) in dimethylformamide (DMF) and an annealing step at 50 °C for 24 hours. The self-healing properties are characterized by visual inspection, rheological and impedance spectroscopy measurements: the results are compared with those of a fatty acid-based molecular organogel chosen as a reference system. The creep-recovery analysis uses the Burgers model for low strains and characterizes a recovery capability of up to 72% of the deformation in Ni2BTC gels while it is only 32% for the fatty acid organogel. At very large strains, the impedance spectroscopy confirms the slow repairing process consistently with the visual observations. Rheological measurements demonstrate the restructuring of the fractured networks. The fatigue of the self-healed gel networks undergoing long sequences of strain-relaxation steps is characterized.

Off-line coupled electrocatalytic oxidation and liquid phase polymer based retention (EO-LPR) techniques to remove arsenic from aqueous solutions

Electrochemistry and membrane ultrafiltration methods (electro-oxidation and liquid phase polymer based retention technique, LPR, respectively) were off-line coupled to remove As(III) inorganic species from aqueous solutions. Our main objective was to achieve an efficient extraction of arsenic species by associating a polymer-assisted liquid phase retention procedure, based on the As(V) adsorption properties of cationic water-soluble polymers, with an electrocatalytic oxidation process of As(III) into its more easily removable analogue As(V). The electrocatalytic oxidation of As(III) to As(V) was performed in the presence of different water-soluble poly(quaternary ammonium) salts acting also as supporting electrolyte, i.e. poly(vinylbenzyl)trimethyl ammonium chloride, P(ClVBTA), poly[3-(methacryloylamine)propyl]trimethyl ammonium chloride, P(ClMPTA), and poly(4-vinyl-1-methylpyridinium bromide), P(BrVMP). After complete electrocatalytic conversion of As(III) into As(V), the mixtures were introduced into an LPR cell to remove the As(V)-polymer adducts. Using P(ClMPTA), P(ClVBTA), or P(BrVMP) ammonium salts in a 20:1 polymer:As(III) mol ratio at pH 8, complete (100%) retention of the arsenic was achieved. Moreover, the As(V) retention efficiency turned out to be directly related to the net charge consumed during the electrochemical conversion of As(III) to As(V).