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International audience; The synthesis and characterization of a series of quaterthiophenes (4Ts) with thiolate groups protected with 2-cyanoethyl (CNE), 2-trimethylsilylethyl (TMSE), and acetyl (Ac) groups are described. Sequential cleavage of these different protecting groups allows for the preparation of 4Ts derivatized with ferrocene and/or alkanethiol chains. The electrochemical behavior of these compounds has been analyzed in solution by cyclic voltammetry (CV). A ferrocene-derivatized dithiol 4T 14 and a dithiol 4T 15 with two TMSE-protected thiolate groups have been immobilized on a gold surface as monolayers that have been characterized by CV, ellipsometry, contact-angle measurement, and X-ray photoelectron spectroscopy (XPS). The results show that molecules 14 and 15 are doubly grafted with a horizontal orientation of the conjugated system relative to the surface. Furthermore, application of the deprotection/alkylation sequence of the remaining protected thiolate groups on a monolayer of 15 allows for efficient post-functionalization.

We present a study of Förster resonance energy transfer (FRET) between two emissive conjugated polyelectrolytes (CPEs) in layer-by-layer (LbL) self-assembled films as a means of examining their organization and architecture. The two CPEs are a carboxylic acid functionalized polyfluorene (PFl-CO(2)) and thienylene linked poly(phenylene ethynylene) (PPE-Th-CO(2)). The PFl-CO(2) presents a maximum emission at 418 nm, while the PPE-Th-CO(2) has an absorption λ(max) centered at 431 nm, in sufficient proximity for effective FRET. Several LbL films have been constructed using varied concentrations of the deposition solutions and identity of the buffer layers separating the two emissive layers, using a system of either weak polyelectrolytes, poly(allylamine hydrochloride) (PAH)/poly(sodium methacrylate) (PMA), or strong polyelectrolytes, poly(diallylammonium chloride) (PDDA)/poly(styrene sulfonate) sodium (PSS). The efficiency of FRET has been monitored using fluorescence spectroscopy. Initially, the fluorescence of the PFl-CO(2) (E(g) ∼ 3.0 eV), which emits at 420 nm, is quenched by the lower band gap PPE-Th-CO(2) (E(g) ∼ 2.5 eV). For films using the PAH/PMA system as buffer bilayers and deposited from 1 mM solutions, the PFl-CO(2) fluorescence is progressively recovered as the number of intervening buffer bilayers is increased. Ellipsometry measurements indicate that energy transfer between the two emissive layers is efficient to a distance of ca. 7 nm.

International audience; Conjugated polymers of hybrid structure containing cyanovinylene linkages have been synthesized by Knoevenagel condensation of diformyl terthienyls with para-dicyanomethylbenzene. UV–vis and cyclic voltammetric data show that these polymers combine reduced band gap, improved light-harvesting properties and low lying HOMO level. Whereas the very low solubility of the polymers did not allow the fabrication of bulk heterojunction solar cells, bilayer heterojunction solar cells have been realized using thermally evaporated films of fullerene C60 as acceptor material. The best devices show a maximum external quantum efficiency of ∼20% and a power conversion efficiency of 0.40% under simulated AM 1.5 solar illumination.

A crown-ether dithiol quaterthiophene is synthesized for its covalent immobilization by double fixation on gold surface. While the corresponding dithioester precursor exhibits Pb2+ complexation properties in solution as evidenced by UV-vis spectroscopy and cyclic voltammetry, this Pb2+ affinity is still maintained for monolayers of the dithiol on gold. In addition, current-voltage measurements by Eutectic GaIn drop contact on the monolayer show a significant increase (up to 1.6 x 1E3) of the current at low bias after Pb2+ complexation., Comment: Paper and supplementary information; Advanced Materials (on line, 2012)

International audience; Regioregular poly[3-(3,6-dioxaheptyl)thiophene] (PDHT) has been synthesized by Grignard metathesis (GRIM). The UV–vis absorption spectrum of spin-cast films of PDHT presents a well-resolved vibrational fine structure typical of well-ordered polymers. The characterization of bulk heterojunction solar cells fabricated using PCBM as acceptor shows that PDHT leads to power conversion efficiencies in ca 4–5 times lower than that obtained with regioregular poly(3-hexylthiophene) (P3HT). In contrast, the characterization of bilayer solar cells realized by thermal evaporation of C60 on spin-cast polymer films shows that PDHT leads to performances similar or even better than P3HT both before and after thermal treatment.