Jean-Manuel Raimundo

Thiophene-based push–pull chromophores for small molecule organic solar cells (SMOSCs)

The last decade has witnessed rapid progress in organic photovoltaics boosted by the design and synthesis of novel π-conjugated small donor–acceptor molecules (mainly thiophene-based chromophores) and by the control and optimization of both device processing and fabrication. Although some important progress has been reached, current challenges remain to further improve their efficiency, durability and cost-effectiveness in order to compete with silicon-based solar cells. This review will provide the scientific community with both general and in depth information on the structure–property relationships related to the photocurrent efficiencies comprising detailed I/V characteristics. It will highlight guidelines for designing new efficient and emerging alternatives to conjugated polymers on the basis of thiophenic chromophores representing, to date, the most widely used class of organic materials for such a purpose as well as important information on device processing or fabrication factors that could influence their performances.

Structure properties relationships of liquid crystal bent core organic semiconductors based on benzo[2,1-b:3,4-b′]dithiophene-4,5-dione

We report the synthesis of a new diketone bridged dithiophene end-capped with the mesogenic functionalities: 2,7′-bis(alkoxy-biphenyl) and 2,7′-bis(alkoxy-phenyl)-benzo[2,1-b:3,4-b′]dithiophene-4,5-dione. Optical and electrochemical properties in solution were investigated by UV-visible absorption and cyclic voltammetry. Liquid crystal properties of these new materials were investigated by differential scanning calorimetry, optical polarizing microscopy, and X-ray diffraction studies. Both compounds exhibit layered phases though there are differences in the organisation of the phase structures. Thin films were implemented as active layers into organic thin-film transistors to evaluate the charge transport properties.

Label free femtomolar electrical detection of Fe(III) ions with a pyridinone modified lipid monolayer as the active sensing layer

An innovative MOS-type field effect transistor was developed for the electrical detection of ferric ions. The sensing assays clearly show a specific detection with a gate-source voltage shift of up to 200 mV and a wide linear detection range (5 × 10-14 to 5 × 10-5 M) associated with good stability, selectivity and reproducibility.

Pd(dba)2 vs Pd2(dba)3: An in-Depth Comparison of Catalytic Reactivity and Mechanism via Mixed-Ligand Promoted C–N and C–S Coupling Reactions

With the help of mixed ligand catalytic systems, the analogous mechanisms behind the cognate performance by Pd(dba)2 and Pd2(dba)3 in catalyzing C-N and C-S coupling reactions were demonstrated. This information is instrumental in organic synthesis requiring Pd-catalyzed cross-coupling reactions and may also be valuable to other Pd-catalyzed transformations.

A field effect transistor biosensor with a γ-pyrone derivative engineered lipid-sensing layer for ultrasensitive Fe3+ ion detection with low pH interference.

Field effect transistors have risen as one of the most promising techniques in the development of biomedical diagnosis and monitoring. In such devices, the sensitivity and specificity of the sensor rely on the properties of the active sensing layer (gate dielectric and probe layer). We propose here a new type of transistor developed for the detection of Fe(3+) ions in which this sensing layer is made of a monolayer of lipids, engineered in such a way that it is not sensitive to pH in the acidic range, therefore making the device perfectly suitable for biomedical diagnosis. Probes are γ-pyrone derivatives that have been grafted to the lipid headgroups. Affinity constants derived for the chelator/Fe(3+) complexation as well as for other ions demonstrate very high sensitivity and specificity towards ferric ions with values as high as 5.10(10) M and a detected concentration as low as 50 fM.

Columnar self-assembly of a 3D-persulfurated coronene asterisk. The dominant role of aryl-sulfur bonds

The synthesis, adsorption behavior, surface structure, and the charge transport properties of a persulfurated coronene asterisk with a 3D-polyaromatic system, namely dodecakis(phenylthio)coronene (DPTC), deposited on HOPG(0001) and Au(111) surfaces, are investigated by means of scanning tunneling microscopy (STM) and spectroscopy (STS). DPTC molecules adsorbed on HOPG(0001) show an orbital mediated tunneling through mainly undisturbed frontier molecular states. DPTC molecules self-assemble on Au(111) into a highly ordered π-stacked columnar “edge-on pattern. The columnar stacking is a gold surface mediated process, as ascertained by fluorescence correlation spectroscopy (FCS). DPTC was monomeric in the precursor solution before assembly. The tunneling spectra of ordered DPTC stacks on Au(111) show an energetic splitting of the frontier molecular states, indicating orbital overlap and supramolecular π–π interactions of adjacent molecules. DPTCs are sufficiently flexible to facilitate dense 1D stacks. The multiple aryl-sulfur bonds play a dominant role in the modulation of the self-assembly properties of the coronenes which in turn affect their electronic properties. Our results encourage further applications in dendrimer chemistry toward molecular electronics, by using the functionalized coronene core and its multidirectional 3D properties.

Synthesis, self-assembly and characterization of a novel push–pull thiophene-based chromophore on a gold surface

Push–pull chromophores are widely used and investigated due to their intrinsic electro-optical and non-linear optical properties that are suitable for a variety of applications. However, the grafting and the control of self-organization of such derivatives onto surfaces have been less considered although this may enhance the pre-cited properties and/or enlarge the scope of their use. In this work we present the stepwise synthesis of a novel non-charged push–pull chromophore modified with a fleeting thioacetate group, and the study of its self-assembling abilities onto a gold surface. Self-assembled dense monolayer formation is clearly demonstrated by electrochemical, XPS and STM measurements. Besides, associated with good film quality a conducting behavior consistent with the structure of the SAM-organized push–pull is also highlighted.

RAFT-synthesized polymers based on new ferrocenyl methacrylates and electrochemical properties

Herein are reported the synthesis and the full characterization of three new ferrocenyl monomers, namely 2-(ferrocenylmethoxy)ethyl methacrylate (FMOEMA), 3-(ferrocenylmethoxy)propyl methacrylate (FMOPMA) and 4-(ferrocenylmethoxy)butyl methacrylate (FMOBMA), synthesized from ferrocenemethanol. Homopolymers were prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization in toluene at 70 °C using 2-cyanoprop-2-yl-dithiobenzoate (CPDB) as a chain transfer agent. Polymerization kinetics were compared to those of the well-known 1-ferrocenylmethyl methacrylate (FMMA). The ferrocenyl containing monomers with alkoxy linkers were found to be as reactive as FMMA in RAFT polymerization. Polymers with controlled molar masses with dispersities lower than 1.5 were obtained. The chemical structures of the monomers and polymers were fully characterized by NMR and size exclusion chromatography. Glass transition temperatures of these methacrylic polymers ranged from 36 °C to 2 °C when controlling the length of the alkoxy linker between the ferrocene unit and the backbone. The electrochemical properties of the monomers and the homopolymers were demonstrated using cyclic voltammetry.

Antibacterial activities of mono-, di- and tri-substituted triphenylamine-based phosphonium ionic liquids

We report the synthesis of new mono, di and tri phosphonium ionic liquids and the evaluation of their antibacterial activities on both Gram-positive and Gram-negative bacteria from the ESKAPE-group. Among the molecules synthesized some of them reveal a strong bactericidal activity (MIC = 0.5 mg/L) for Gram-positive bacteria (including resistant strains) comparable to that of standard antibiotics. A comparative Gram positive and Gram negative antibacterial activities shows that the nature of counter-ion has no significant effects. Interestingly, the increase of phosphonium lateral chains (from 4 to 8 carbons) results in a decrease of antibacterial activities. However, the increase of the spacer length has a positive influence on the activity on both Gram-positive and Gram-negative bacteria except for E. aerogenes. Finally, the increased charge density has no effect on the Gram-positive antibacterial activities (MIC between 2 and 4 mg/L) but seems to attenuate (except for P. aeruginosa) the discrimination between Gram-positive and Gram-negative. Overall these results suggest a unique mechanism of action of these triphenylamine-phosphonium ionic liquid derivatives.

Electrical and Optical Measurements of the Bandgap Energy of a Light-Emitting Diode.

Semiconductors materials are at the basis of electronics. Most electronic devices are made of semiconductors. The operation of these components is well described by quantum physics which is a little mysterious to students. One of the intrinsic parameters of semiconductors is their bandgap energy Eg. In the case of light-emitting diodes (LEDs) Eg fixes the colour of the light emitted by the diodes. We propose in this article a lab work allowing a comparison of Eg of a green LED obtained by both electrical and optical measurements. The two slightly different results can be explained by the theoritical knowledges of the students on solid physics and electronic devices internal architecture.