Charlotte Mallet

Survey of recent advances of in the field of π-conjugated heterocyclic azomethines as materials with tuneable properties

This account gives an overview of our recent work in the area of conjugated azomethines derived from 2-aminothiophenes. It will be presented that mild reaction conditions can be used to selectively prepare symmetric and unsymmetric conjugated azomethines. It further will be demonstrated that azomethines consisting of various 5-membered aryl heterocycles lead to chemically, reductively, hydrolytically, and oxidatively robust compounds. The optical and electrochemical properties of these materials can be tuned contingent on the degree of conjugation, type of aryl heterocycle, and by including various electronic groups. The end result is materials having colors spanning 250 nm across the visible spectrum. These colors further can be tuned via electrochemical or chemical doping. The resulting doped states have high color contrasts from their corresponding neutral states. The collective opto-electronic properties and the means to readily tune them, make thiophenoazomethine derivatives interesting materials for potential use in a gamut of applications.

Facile Synthesis of 3-Alkoxy-4-cyanothiophenes As New Building Blocks for Donor−Acceptor Conjugated Systems

3-Alkoxy-4-cyanothiophenes are efficiently synthesized in two steps from the readily available 4-cyano-3-oxotetrahydrothiophene. Regioisomers of bithiophene derivatives are easily synthesized by playing on the strong electronic dissymmetry of the thiophene ring induced by the alkoxy and cyano groups.

Unparalleled fluorescence of a polyazomethine prepared from the self-condensation of an automer and its potential use as a fluorimetric sensor for explosive detection

A novel fluorescent monomer consisting of complementary amino and aldehyde functional groups was prepared via the Buchwald–Hartwig coupling protocol. The monomer self-condensed to yield a π-conjugated regioregular polyazomethine that fluoresced in 48% in solution. The value measured by absolute methods is the highest reported fluorescence quantum yield for conjugated polyazomethines. The polymer was used a fluorimetric sensor for explosive analytes.

Synthesis and Electronic Properties of D–A–D Triads Based on 3-Alkoxy-4-cyanothiophene and Benzothienothiophene Blocks

3-Alkoxy-4-cyanothiophene units are used as building block for the synthesis of conjugated donor-acceptor-donor (D-A-D) triads. The donor part consists of benzothienothiophene end groups associated with the alkoxy groups of the 3-alkoxy-4-cyanothiophene, while the central acceptor part is formed by combining the electron-withdrawing cyano group with thiophene or benzothiadiazole units.

Rational Topological Design for Fluorescence Enhancement upon Aggregation of Distyrylfuran Derivatives

A series of 2,5-distyrylfuran derivatives bearing pentafluorophenyl- and cyanovinyl units have been synthesized for aggregation-induced emission (AIE). The effect of the type and extent of the supramolecular connections on the AIE of the furan derivatives were examined and correlated with their X-ray crystal structures. It was found that the simultaneous presence of cyano and perfluorophenyl units strongly enhances the fluorescence upon aggregation. Single-crystal X-ray diffraction analysis confirmed that CH⋅⋅⋅F, F⋅⋅⋅F, CH⋅⋅⋅nitrile, Ar⋅⋅⋅ArF (Ar=aryl, ArF =fluoroaryl), and nitrile⋅⋅⋅ArF intra- and intermolecular interactions drive the topology of the molecule and that solid-state supramolecular contacts favor AIE of the furan derivatives.

Competition between π–π or furan–perfluorophenyl stacking interactions in conjugated compounds prepared from azomethine connections

Conjugated compounds associating phenyl or pentafluorophenyl units linked viaazomethine bonds to a central furan or furylene–vinylene moiety have been synthesized. The crystal structures of compounds end capped with perfluorophenyl units are analyzed in terms of intermolecular interactions involving the C–HF contacts, π–π interactions and furan–perfluorobenzene interactions. The compound with a furan moiety as spacer presents a stacking mode defined by C–H–F contacts and π–π interactions while the compound based on a furylene–vinylene unit shows a packing pattern exclusively due to strong furan–perfluorobenzene interactions.

Spin transport in benzofurane bithiophene based organic spin valves

In this paper we present spin transport in organic spin-valves using benzofurane bithiophene (BF3) as spacer layer between NiFe and Co ferromagnetic electrodes. The use of an AlO x buffer layer between the top electrode and the organic layer is discussed in terms of improvements of stacking topology, electrical transport and oxygen contamination of the BF3 layer. A study of magnetic hysteresis cycles evidences spin-valve behaviour. Transport properties are indicative of unshorted devices with non-linear I-V characteristics. Finally we report a magnetoresistance of 3% at 40 K and 10 mV in a sample with a 50 nm thick spacer layer, using an AlO x buffer layer.

Unprecedented Demonstration of Regioselective SEAr Reaction giving Unsymmetrical Regioregular Oligothiophenes

Aromatization of 4-cyano-3-oxotetrahydrothiophene by sulfuryl chloride gives the new building block 4-cyano-3-pyrrolidylthiophene, which forms unsymmetrical regioregular oligothiophenes with a strict alternation of the donor and acceptor groups along the conjugated system. The self-coupling reactions that form the oligomers are shown to proceed by a regioselective electrophilic aromatic substitution mechanism involving a stabilized Wheland intermediate.

Topological and packing mode modification for solid-state emission enhancement of bis(perfluorostyryl)furan derivatives

An unsymmetric bis(perfluorostyryl)furan with a cyanovinyl unit was prepared (F1). Its crystallographic structure was resolved along with its cyano vinylene (1) and unsubstituted (2) aldehyde precursors. F1 was found to form ribbons involving C–H⋯F interactions, while also having multiple intermolecular contacts, including C–F⋯Fπ and π–π interactions. These contacts also occurred when F1 aggregated in 9:1 water/THF mixtures. When the supramolecular contacts are engaged, the emission intensity of F1 increases, with absolute emission yields of 9 and 25% occurring in aggregates and powder, respectively.