Alain Gorgues

Immobilization of Redox-Active Ligands on an Electrode: The Dendrimer Route

Macrocyclic systems that respond electrochemically when interacting with a guest ion have been extensively studied,[1] notably in connection with their potential applications as chemosensors. In such host molecules, the complexing ability of the ligand can be tuned by the electrochemical potential applied. Most of these compounds are built by covalent grafting of a receptor subunit onto a redox-active component. Thus, in the case of metal-cation recognition, various ligating fragments, for example, crown ethers, have been attached to an electroactive moiety such as a metallocene or a quinone derivative.[1] Alternatively, the ability of the tetrathiafulvalene (TTF) core to act as the redox-active subunit is now well established.[2] Indeed, TTF derivatives are able to exist in three different stable redox stages (neutral, radical cation, and dication) and therefore allow the electrochemical release of metallic cations to be controlled. A further exciting challenge, less explored, lies in the preparation of sensing devices that can transfer the abovementioned recognition properties, observed in solution, at the interface of a solid electrode and a liquid.[3] Results in this direction have been obtained thanks to a) electropolymerization of suitably substituted redox-responsive ligands (e.g., a pyrroleor a thiophene-based monomer),[3, 4] and b) preparation of self-assembled monolayers.[5] Modified electrodes were also recently obtained by Casado et al. by electrodeposition of organometallic-containing silicon dendrimers.[6] On the other hand, TTF dendrimers, possessing 21 TTF moieties in the highest generation, were described by Bryce et al. ,[7] but no mention was made of their immobilization on an electrode surface. We describe here the synthesis of a series of dendrimers with up to 96 redox-active TTF moieties on the periphery, which allow the generation of polycationic species bearing up to 192 positive charges on the surface. Modified electrodes incorporating these electroactive TTF dendrimers were Experimental Section

2-Mono or 2,3-Bis(hydroxymethyl)-6,7-ethylenedithio-tetrathiafulvalenes: New potential precursors of organic metals endowed with hydrogen bonds

Abstract The syntheses of new π-unsymmetrical donors of the TTF family having half moiety of bis(ethylenedithio)-TTF (BEDT-TTF) and half moiety of TTF substituted with one (or two) hydroxymethyl group(s) are described. Their good π-donating ability is demonstrated by cyclic voltammetry.

2,5-Bis(1,4-dithiafulven-6-yl) furans, thiophenes and N-methyl pyrroles as extended analogues of tetrathiafulvalene

Abstract The title compounds are synthesized by Wittig or Wittig-Horner reactions between the corresponding furan, thiopen and N-methyl-pyrrole-2,5-dicarbaldehydes and P-reagents W or P bearing the 1,3-dithiol-2-ylidene moiety adequately substituted at the 4,5-positions; thanks to usual and thin layer cyclic voltammetry, they are shown to possess good π-donor abilities.

The bis-linking of tetrathiafulvalene (TTF) to C60: Towards the control of electron transfer between π-donors and C60

The bis-linking of a tetrathiafulvalene (TTF) to C60 is carried out by [4+2] Diels-Alder cycloaddition of C60 to the 2,3-dimethylene-TTF 2, this transient diene being generated by KI-[18]crown-6 mediated dibromine reductive elimination of the 2,3-bis(bromomethyl)TTF 3. The C60-TTF target cycloadduct 1a is charaterized by spectroscopy and electrochemical study.

Do π-dimers of tetrathiafulvalene cation radicals really exist at room temperature?

The longest wave absorption band of the tetramethylthio- tetrathiafulvalene cation radical, which is usually interpreted as a π-dimer band, is shown to be the intrinsic cation radical absorption, all studied cation radicals in solution at room temperature exist as paramagnetic monomers and only tetrathiafulvelene and tetramethyltetrathiafulvalene cation radicals undergo π-dimerization at low temperatures.

Extended analogues of tetrathiafulvalene (TTF): 1,2-bis, 1,4-bis and 1,2,4,5-tetrakis(1,4-dithiafulven-6-yl) benzenes; Synthesis and π-donor abilities.

Abstract The title compounds are prepared by Wittig or Wittig-Horner reactions between the corresponding benzenes di- and tetracarbaldehydes and the P-reagents W or P bearing the 1,3-dithiol-2-ylidene moiety; among them, the tetrakis(dithiafulvenyl)benzene 3c is shown by cyclic voltammetry to possess the best π-donor character and, also, is chemically or electrochemically oxidized.

Tetraformyltetrathiafulvalene (TFTTF) and acetals, precursors of polyfunctionalized TTFs.

Abstract A short synthesis of 1,3-dithiol-2-thiones bearing two aldehyde functionalities, free and/or masked as diethylacetals is described. They are shown to be convenient precursors for synthesizing di- and tetraformyl-TTF. When submitted to four-fold nucleophilic attacks, the latter readily affords new substituted derivatives such as the bis-(pyridazino)-TTF 8 , the tetrakis-(hydroxymethyl)-TTF 9 and the tetravinylic-TTF 10 whose π-donor ability has been characterized.

Rigidified tetrathiafulvalene–[60]fullerene assemblies: towards the control of through-space orientation between both electroactive units

Our recent works on fused TTF–C60 dyads, (TTF)n–C60 polyads and C60–TTF–C60 dumbbell triads in which the acceptor C60 is doubly tethered to the donor tetrathiafulvalene through a rigidified cyclohexene ring are presented. This approach was developed in order to control the relative orientation as well as the distance between both donor and acceptor entities. Thereby, through-space interactions which are of great importance for photoinduced electron- and/or energy-transfer processes are expected to dominate because of the special topology of the molecules. The two linked C60 and TTF chromophores in such adducts are not only in close proximity but also have optimal orbital orientations, thus facilitating these through-space electronic interactions. These new C60-based assemblies were synthesized by [4 + 2] Diels–Alder cycloaddition reactions. The different methodologies considered for their synthesis are discussed, their analytical, spectroscopic characterizations and electrochemical properties are also described. The selective electro-oxidation or reduction afforded the corresponding radical cation and radical anion which were characterized by EPR. These C60-based assemblies were studied for their nonlinear optical and optical limiting applications. Moreover, intramolecular photoinduced charge-separation and charge-recombination processes in a fused C60–TTF–C60 dumbbell triad which was designed to be soluble in organic solvents were investigated by time-resolved absorption and fluorescence techniques. Appreciable interaction between the C60 moiety and TTF moiety in the ground state was suggested by steady-state absorption spectra and the fluorescence spectra showed considerable interaction in the singlet excited state. The nanosecond transient absorption spectra displayed the formation of the charge-separated radical pair C60–TTF˙+–C60˙−, characterized by a lifetime of ca. 20 ns in benzonitrile.

The synthesis of 4,4'(5')-diformyltetrathiafulvalene

The synthesis of the title compound 9, by three different routes, is described for the first time.

Oxidative dimerization of 2-(1,4-dithiafulven-6-yl)thiophenes: an alternative route towards extensively π-conjugated tetrathiafulvalene analogs

Abstract Extended tetrathiafulvalene analogs with dienic or bithienylic conjugated spacers have been synthesized by oxidative dimerization of 1,4-dithiafulvenylthiophenes.