Pierre Frère

3,4-Ethylenedioxythiophene (EDOT) as a versatile building block for advanced functional π-conjugated systems

The potentialities offered by EDOT as a building block for the synthesis of functional π-conjugated systems are reviewed. The first part underlines the specific advantages of the EDOT unit for the design of precursors of electrogenerated functional conducting polymers combining high reactivity and low polymerization potential. This topic is illustrated by some recent examples of polymers with specific electrochemical properties and/or a reduced band gap. The second part is focused on the interest of EDOT as a building block for the synthesis of various classes of molecular functional π-conjugated systems. Examples of fluorophores, push–pull chromophores for nonlinear optics and extended π-donors are presented. Emphasis is placed on the optical and crystallographic structure of these compounds, which shows that a major advantage of the EDOT building block lies in an unique combination of strong electron donor properties and self-structuring effects related to intramolecular non-covalent interactions between oxygen and sulfur. Such intramolecular interactions also exert a determining influence on the structure and electronic properties of π-conjugated oligomers incorporating EDOT units which represent some of the more recent uses of the EDOT building block. The structure–property relationships of various classes of EDOT-containing conjugated oligomers are discussed in relation to their potential use as organic semi-conductors. In a brief last section, various synthetic approaches devoted to the chemistry of EDOT itself, or to the modification of its chemical structure, are discussed in relation with possible future research directions.

Push–pull chromophores based on 2,2′-bi(3,4-ethylenedioxythiophene) (BEDOT) π-conjugating spacer

Abstract Replacement of 2,2′-bithiophene by BEDOT in push–pull NLO-phores produces a red shift of the absorption maximum accompanied with a large increase of the quadratic nonlinear optical susceptibility.

EXTENDED THIENYLENEVINYLENE OLIGOMERS AS HIGHLY EFFICIENT MOLECULAR WIRES

A much smaller band gap than in the parent polymer is observed for the π-conjugated hexadecamer 1, which can be reversibly charged up to the hexacation in a small potential range.

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.

Third-order nonlinear optical properties and two-photon absorption in branched oligothienylenevinylenes

Abstract We report measurements of the third-order susceptibilities and two-photon absorption in branched oligothienylenevinylenes derivatives C 42 H 62 S 2 , C 114 H 174 S 6 , C 252 H 366 N 3 O 6 P 3 S 12 , using degenerate four wave mixing (DFWM) technique at λ=532 nm in picosecond regime. All the studied compounds show large third-order nonlinear optical properties with comparison with known materials such as, polydiacetylene, octupolar molecules and their dipolar subunits. We show the influence of the number of branches on the benzene cycle. We demonstrate that the values of third-order susceptibilities χ 〈3〉 and two-photon absorption coefficients β increase as the number of branches increase. As consequence the studied complexes can be very interesting for optical limiting applications.

Mixed π-conjugated oligomers of thiophene and 3,4-ethylenedioxythiophene (EDOT)

Abstract Conjugated oligomers based on various combinations of thiophene and 3,4-ethylenedioxythiophene (EDOT) moieties have been synthesised. Comparison of the optical and electrochemical properties shows that the introduction of a bis-EDOT core in the middle of the system produces a decrease of the HOMO–LUMO gap which is attributed to an enhancement of the planarity and rigidity of the π-conjugated system.

Linearly extended tetrathiafulvalene analogues with fused thiophene units as π-conjugated spacers

A new series of linearly extended tetrathiafulvalene analogues with thienothiophene and dithienothiophene π-conjugating spacers has been synthesized. Electronic absorption spectra present a vibronic fine structure typical for rigid conjugated systems. Investigation of the electrochemical behaviour of the new donors by cyclic voltammetry reveals the successive generation of stable radical cation and dication species. The crystallographic structure of a single crystal of a dication salt of TT-TTF(ClO4)2 has been analysed by X-ray diffraction. The dication presents a syn conformation stabilised by S⋯S intramolecular interactions. The quinoid structure expected for the spacer for the +2 oxidation state is clearly revealed by the bond lengths.

3,4-Phenylenedioxythiophene (PheDOT): a novel platform for the synthesis of planar substituted π–donor conjugated systems

3,4-Phenylenedioxythiophene (PheDOT), a benzenic analogue of 3,4-ethylenedioxythiophene (EDOT), has been synthesized using two different routes namely etherification of 2,5-dicarboethoxy-3,4-dihydroxythiophene with halo-aromatics and transetherification of 3,4-dimethoxythiophene with catechols. Quantum calculations and electrochemical measurements show that replacement of the ethylene bridge of EDOT by a phenyl group leads to an increase of the HOMO level and to a stabilization of the cation radical, making electropolymerization of PheDOT more difficult than that of EDOT. The synthesis of several PheDOT derivatives is described together with preliminary results on their electrochemical polymerization and on the properties of the resulting polymers and copolymers.

(C4H3SCH2NH3)2(CH3NH3)Pb2I7 : non-centrosymmetrical crystal structure of a bilayer hybrid perovskite

The analysis of the crystal structure of (C4H3SCH2NH3)2(CH3NH3)Pb2I7, displaying a well-ordered acentric inorganic Pb2I7(3-) bilayer, is reported, and compared to the related monolayer hybrid perovskite.

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.