Olivier Alévêque

Effects of aromatic spacers on the properties of organic field effect transistors based on π-extended tetrathiafulvalene derivatives

OFETs built from extended TTF derivatives containing N-methylpyrrole, furan, thiophene and benzene with meta or para linkages as spacers are presented. The aromatic spacer plays a crucial role in the characteristics and stability of the OFETs. The less conjugated derivative with a meta-benzene moiety as spacer has the best mobility, with a higher on/off ratio and strongly enhanced stability in air.

Indolinooxazolidine: a versatile switchable unit.

The design of multiresponsive systems continues to arouse a lot of interest. In such multistate/multifunctional systems, it is possible to isomerize a molecular system from one metastable state to another by application of different stimulation such as light, heat, proton, or electron. In this context, some researches deal with the design of multimode switch where a same interconversion between two states could be induced by using indifferently two or more different kind of stimuli. Herein, we demonstrate that the association of an indolinooxazolidine moiety with a bithiophene unit allows the development of a new trimode switch. A reversible conversion between a colorless closed form and a colorful open form can be equally performed by light, proton, or electrical stimulation. In addition, the oxidation of this system allows the generation of a third metastable state.

Phase segregation on electroactive self-assembled monolayers: a numerical approach for describing lateral interactions between redox centers.

A numerical method is proposed in order to differentiate a random distribution from a phase segregation of redox centers on (mixed) SAMs. This approach is compared to Lavirons interactions model and voltammetric data of nitroxylalkanethiolate SAMs.

Nitroxyl Radical Self-Assembled Monolayers on Gold: Versatile Electroactive Centers in Aqueous and Organic Media

Since the pioneering work by Nuzzo and Allara in 1983, selfassembled monolayers (SAMs) of alkanethiols have gained much attention in the interfacial electrochemistry and other research fields. 3] During the last decade, 5] increasing attention has been dedicated to the design and elaboration of redox-responsive SAMs. Employing redox SAM-modified electrodes for catalysis, recognition and sensing have resulted in some elegant examples that incorporate sophisticated receptors on the electrode surfaces. However, to the best of our knowledge, no redox-responsive SAM was designed to be active and stable in both aqueous (on wide range of pH) and organic media. TEMPO (2,2,6,6-Tetramethylpiperidine-1-oxyl) and its derivatives (under their oxoammonium form) have been extensively studied in the search for organic synthesis as a redox mediator, mostly, for the oxidation of primary alcohols. The electrochemical oxidation of TEMPO is known to be a stable and reversible one-electron process in both aqueous and non-aqueous electrolytes. 13] Despite the wide electrochemical applications of nitroxyl radical, rare works have been devoted to design and elaborate of redox-responsive TEMPO SAMs. In 1997, Fuchigami et al. reported the first preparation of stable self-assembled TEMPO-modified electrodes in acetonitrile : the electrochemical stability was only reached with highly diluted mixed SAMs of nitroxyl radical derivative and hexadecanethiol. In 1999, Kashiwagi et al. reported electrocatalysis attempts of amines with a mixed SAM of chiral nitroxyl radical derivative and hexadecanethiol : as mentioned by authors, results could be applied to the determination of optical purity of chiral amines. After a ten-years pause, Finklea et al. worked on Au-SACHTUNGTRENNUNG(CH2)10C(O)N(H)-TEMPO SAM to the first estimation of the standard rate constant and the reorganization energies of TEMPO/TEMPO in 1 m H2SO4. Herein, we raised the challenge of a design of redox-responsive TEMPO SAMs to be active, stable and providing electrocatalytic activities in both aqueous and non-aqueous solvents. To reach this goal, we synthesized the three nitroxyl radical derivates 1 a, 1 b and 1 c shown in Scheme 1. The synthesis of 1 a, 1 b and 1 c were carried out as outlined in Scheme 1. w-thioACHTUNGTRENNUNGacetyl carboxylic acids with different carbon chains length 2 a–c were synthesized from the corresponding w-bromocarboxylic acids by nucleophilic displacement with potassium thioACHTUNGTRENNUNGacetate in DMF. 4-aminoTEMPO was coupled to w-thioacetyl carboxylic acids 2 a-c via the active ester method, using diACHTUNGTRENNUNGcyclohexylcarbodiimide (DCC) and 1-hydroxybenzotriazole (HOBT) in methylene chloride (CH2Cl2), to give the TEMPO derivatives 3 a–c in good yields (77 to 84 %). The thioacetates 3 a–c were subsequently deprotected to thiols 1 a–c, under basic conditions, using CsOH.H2O in a mixture of THF and MeOH (yields: 50 to 91 %). Cyclic voltammograms (CVs) of 3 a, 3 b or 3 c exhibit a reversible one-electron process in CH2Cl2 and CH3CN, close to 0.56 V and 0.41 V (vs Ag/AgNO3 in 0.1 m Bu4NPF6) respectively. The kinetics for the formation of SAMs, prepared on Au substrate from 1 mm solution of 1 a, 1 b or 1 c in CH2Cl2 or CH3CN, were followed by using quartz crystal microbalance (QCM) measurements. By employing, the Langmuir adsorption isotherm model, it is possible to establish that deposition kiScheme 1. Synthesis of nitroxyl radical derivatives 1 a, 1 b and 1 c.

Huge electro-/photo-/acidoinduced second-order nonlinear contrasts from multiaddressable indolinooxazolodine.

In this work, linear and nonlinear optical properties of electro-/acido-/photoswitchable indolino[2,1-b]oxazolidine derivatives were investigated. The linear optical properties of the closed and open forms have been characterized by UV-visible and IR spectroscopies associated with DFT calculations. Nonlinear optical properties of the compounds have been obtained by ex situ and in situ hyper-Rayleigh experiments in solution. We show that protonated, oxidized, and irradiated open forms exhibit the same visible absorption and NLO features. In particular, the closed and open forms exhibit a huge contrast of the first hyperpolarizability with an enhancement factor of 40-45. Additionally, we have designed an original electrochemical cell that allows to monitor in situ the hyper-Rayleigh response upon electrical stimulus. We report notably a partial but good and reversible NLO contrast in situ during oxidation/reduction cycles. Thereby, indolinooxazolidine moieties are versatile trimodal switchable units which are very promising for applications in devices.

A bridged low band gap A–D–A quaterthiophene as efficient donor for organic solar cells

α,ω-Bis(dicyanovinyl)quaterthiophene 1 with a median 4,4-diethyl-4H-cyclopenta[2,1-b:3,4-b′]dithiophene has been synthesized. UV-Vis absorption data show that the covalent bridging of the inner 2,2′-bithiophene leads to a significant reduction of the HOMO–LUMO gap essentially due to an increase of the HOMO level as confirmed by electrochemical and theoretical results. X-ray diffraction analysis of a single crystal of 1 shows that except for the out-of-plane ethyl groups, the conjugated system displays a quasi-planar geometry while the molecular packing exhibits strong π-stacking interactions and multiple short intermolecular contacts. Quaterthiophene 1 has been used as active donor material in organic solar cells of various architectures including bi-layer planar hetero-junctions and hybrid co-evaporated bulk hetero-junctions with C60 as electron acceptor material. A maximum conversion efficiency of 4.30% is obtained with a hybrid co-evaporated device. These results are discussed in terms of structure–properties relationships with reference to the open-chain parent α,ω-bis(dicyanovinyl)quaterthiophene 2.

Evaluation of a new matrix-free laser desorption/ionization method through statistic studies: comparison of the DIAMS (desorption/ionization on self-assembled monolayer surface) method with the MALDI and TGFA-LDI techniques

This work demonstrates that the desorption/ionization on self-assembled monolayer surface (DIAMS) mass spectrometry, a recent matrix-free laser desorption/ionization (LDI) method based on an organic target plate, is as statistically repeatable and reproducible as matrix assisted laser desorption ionization (MALDI) and thin gold film-assisted laser desorption/ionization (TGFA-LDI) mass spectrometries. On lipophilic DIAMS of target plates with a mixture of glycerides, repeatability/reproducibility has been estimated at 15 and 30% and the relative detection limit has been evaluated at 0.3 and 3 pmol, with and without NaI respectively. Salicylic acid and its d(6)-isomer analysis confirm the applicability of the DIAMS method in the detection of compounds of low molecular weight.

Controlling the Host‐Guest Interaction Mode through a Redox Stimulus

A proof-of-concept related to the redox-control of the binding/releasing process in a host-guest system is achieved by designing a neutral and robust Pt-based redox-active metallacage involving two extended-tetrathiafulvalene (exTTF) ligands. When neutral, the cage is able to bind a planar polyaromatic guest (coronene). Remarkably, the chemical or electrochemical oxidation of the host-guest complex leads to the reversible expulsion of the guest outside the cavity, which is assigned to a drastic change of the host-guest interaction mode, illustrating the key role of counteranions along the exchange process. The reversible process is supported by various experimental data (1 H NMR spectroscopy, ESI-FTICR, and spectroelectrochemistry) as well as by in-depth theoretical calculations performed at the density functional theory (DFT) level.

Glycoluril-tetrathiafulvalene molecular clips: on the influence of electronic and spatial properties for binding neutral accepting guests.

Summary Glycoluril-based molecular clips incorporating tetrathiafulvalene (TTF) sidewalls have been synthesized through different strategies with the aim of investigating the effect of electrochemical and spatial properties for binding neutral accepting guests. We have in particular focused our study on the spacer extension in order to tune the intramolecular TTF···TTF distance within the clip and, consequently, the redox behavior of the receptor. Carried out at different concentrations in solution, electrochemical and spectroelectrochemical experiments provide evidence of mixed-valence and/or π-dimer intermolecular interactions between TTF units from two closed clips. The stepwise oxidation of each molecular clip involves an electrochemical mechanism with three one-electron processes and two charge-coupled chemical reactions, a scheme which is supported by electrochemical simulations. The fine-tunable π-donating ability of the TTF units and the cavity size allow to control binding interaction towards a strong electron acceptor such as tetrafluorotetracyanoquinodimethane (F4-TCNQ) or a weaker electron acceptor such as 1,3-dinitrobenzene (m-DNB).

Self-assembled monolayer-assisted mass spectrometry

This article deals with the use of self-assembled monolayers (SAMs) for the formation and characterization of gaseous ions in mass spectrometry (MS). The first part reviews the different results reported in the literature concerning the use of SAMs for surface induced dissociation (SID) of produced ions into a mass spectrometer. In SID/MS, the ion collision at a given kinetic energy allows the accumulation of internal energy for reaching the activation energy of fragmentation reactions. The different chemical structures of SAMs in SID/MS are described and their influence on the amount of the kinetic energy (Ekin) converted into internal energies (Eint) is reported. The second part is dedicated to the implication of SAMs in the laser desorption–ionization (LDI) methods allowing gas-phase ion formation and highlights the specifications required for the SAMs elaboration in the LDI/MS application field. The matrix-free LDI method is more particularly described. The results obtained with the so-called DIAMS technique (desorption–ionization on self-assembled monolayer surface) are reported and the organization and stability of SAMs are pointed out to obtain reliable results in LDI/MS.