EDOT Units Research Articles

Molecular and supramolecular engineering of π-conjugated systems for photovoltaic conversion

Various series of conjugated systems have been used as donor in hetero-junction solar cells. The results obtained with EDOT-containing π-conjugated oligomers show that besides their direct effect on the electronic properties of the conjugated chain, the number and position of the EDOT units control to a large extent the orientation of the molecules on the substrate and hence the performances of the derived solar cells. The characteristics of the cells based on oligothienylenevinylenes donors show that in this case structural control of orientation can be achieved by means of substitution of the conjugated structure by alkyl chains. Donors based on star-shaped oligothiophenes provide another example of control of horizontal molecular orientation by design. The photovoltaic characteristics of bi-layer hetero-junctions show that the combined effects of controlled molecular orientation and planarization of the structure by the use of a fused tri-thienobenzene central core lead to power conversion efficiencies approaching 1%. In order to avoid the need to control molecular orientation first examples of bulk hetero-junctions based on PCBM and three-dimensional conjugated systems with isotropic electronic properties have been realized. A power conversion efficiency of 0.30% has been obtained under 79 mW cm − 2 white light illumination. This result obtained with a 3D donor based on a terthiophene conjugated chain with very limited absorption of the visible spectrum demonstrates the large potentialities of this novel concept.

Synthesis and properties of PEDOT derivatives containing liquid crystalline groups

Abstract We have developed novel liquid crystalline conjugated polymers consisting of alternating blocks of EDOT and phenylene units substituted with two mesogenic groups. The chemical polymerization was carried out in dimethylformamide with a Ni(cod) catalyst. Electrochemical polymerizations were also examined in acetonitrile and tetrahydrofuran. The monomer was electropolymerized onto platinum button and ITO glass electrodes by repeated scanning from −1.6 V to + 1.6 V versus Ag/Ag+ at 20 mV/s. The polymer was electrochromic and reversibly switching from deep purple to emerald green upon oxidation. The polymer structure was confirmed by NMR, IR, GPC, and elemental analysis. Optical absorption and photoluminescence measurements were performed. Thermal and liquid crystalline properties of the polymers were investigated by optical polarizing microscopy and differential scanning calorimetry (DSC). The combination of liquid crystalline (LC) and electrochromic properties allowed us to obtain color tunable liquid crystal materials with optical anisotropy. The polymer may find use as a new functional material for “liquid crystalline electrochromic device”.

Design of Organic Semiconductors: Tuning the Electronic Properties of π‐Conjugated Oligothiophenes with the 3,4‐Ethylenedioxythiophene (EDOT) Building Block

Hybrid oligothiophenes based on a various combinations of thiophene and 3,4-ethylenedioxythiophene (EDOT) groups have been synthesized. UV/Vis absorption spectra show that the number and relative positions of the EDOT groups considerably affect the width of the HOMO-LUMO gap and the rigidity of the conjugated system. Analysis of the crystallographic structure of two hybrid quaterthiophenes confirms that insertion of two adjacent EDOT units in the middle of the molecule leads to a self-rigidification of the conjugated systems by intramolecular SO interactions. Cyclic voltammetry data shows that the first oxidation potential of the oligomers decreases with increasing chain length and increasing number of EDOT groups for a given chain length. Electrochemical studies and theoretical calculations show that the positions of the EDOT units in the conjugated chain control the potential difference (DeltaE(p)) between the first and second oxidation steps. Moving the EDOT groups from the outer to the inner positions of the conjugated system increases DeltaE(p). Theoretical calculations confirm that this phenomenon reflects an increase of the intramolecular coulombic repulsion between positive charges in the dication. A thin-film field-effect transistor was fabricated by vacuum sublimation of a pentamer with alternating thiophene-EDOT structure, and the hole mobility was determined.

Copolymer from electropolymerization of thiophene and 3,4-ethylenedioxythiophene and its use as cathode for lithium ion battery

Electropolymerizations (EPs) of thiophene (Th), 3,4-ethylenedioxythiophene (EDOT) and the mixed monomers of Th and EDOT in 0.05 M Et 4NClO 4/propylene carbonate (PC) solution were performed to prepare polymer films as potential cathode materials in lithium ion battery. The incorporation of EDOT units into pure polythiophene (PTh) chain leads to large alternations on the experimental conditions of EPs and the properties of the resulting polymer films. Onset potential of the EPs was reduced with the participation of EDOT component. The resulting polymers, PTh, poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(thiophene-co-3,4-ethylenedioxythiophene) (PTh–EDOT) were then served as cathode materials to test their capabilities to transport lithium ion in 1.0 M LiPF 6/ethylene carbonate/dimethyl carbonate solution. With the inherent EDOT unit, PEDOT and PTh–EDOT have better charge capacity, stability and response rate than pure PTh. Among the copolymers, PTh–EDOT (1/1) even shows better stability than pure PEDOT homopolymer, advantage of using EDOT as copolymer component is thus evaluated.

Oligothienylenevinylenes incorporating 3,4-ethylenedioxythiophene (EDOT) units

A new series of π-conjugated oligomers based on various combinations of thiophene and EDOT units and double bonds has been synthesized by Wittig–Horner reactions from phosphonate anions carrying EDOT or bis-EDOT units. Optical and electrochemical results evidence the crucial role of the EDOT moiety for modulating the electronic properties of the oligomers. The insertion of bis-EDOT unit in the middle of the molecule leads to a self-rigidification of the conjugated system due to non covalent S⋯O intramolecular interactions. The strong electron donor effect of the EDOT units explains the determining role of the relative position of the EDOT units on the localization and stabilization of the positive charges in the radical cation or dication states.

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.

Crown‐Tetrathiafulvalenes Attached to a Pyrrole or an EDOT Unit: Synthesis, Electropolymerization and Recognition Properties

A crown-tetrathiafulvalene electroactive receptor has been covalently linked to electropolymerizable pyrrole or 3,4-ethylenedioxythiophene monomers. The synthetic route to the monofonctionalized tetrathiafulvalene (TTF) ligand has been optimized. Two derivatives of pyrrole (N- and 3-substituted) were synthesized. The various substituted monomers have been electropolymerized to produce polypyrrole (PP) and poly(ethylenedioxothiophene) (PEDOT) films bearing the electroactive TTF moiety. The electroactivity of the polymer films is efficiently controlled by the well-defined two-step redox behavior of the TTF unit. In the case of PEDOT, an alternative post-polymerization derivatization strategy has been used, involving the grafting of the crown-TTF ligand on the previously grown PEDOT backbone. Though chemical derivatization is realized under heterogeneous conditions, in the bulk of the film, this strategy proved to be particularly efficient. These electrodes constitute the first examples of conducting polymer-based modified electrodes incorporating a TTF electrochemical probe, able to interact with a guest ion, such as Ba2+. The cation recognition properties of these various electrodes have been analyzed by cyclic voltammetry and their electroactivity in water as well as their regeneration capability have been investigated.

Organic Polymeric Electrochromic Devices: Polychromism with Very High Coloration Efficiency

The electrochromic properties of electrodeposited poly(1,4-bis(2-[3‘,4‘-ethylenedioxy]thienyl)-2-methoxy-5-2‘ ‘-ethylhexyloxybenzene) (P(BEDOT-MEHB)), a material for polymer electrochromic displays, are reported in detail. While the polymer is transparent in the fully oxidized state, two absorption bands obtained in the visible region for the neutral and partially oxidized polymer are due to two different colors from the same material. Compared to other inorganic or organic electrochromic materials, the P(BEDOT-MEHB) films exhibited very high coloration efficiency values: as high as 680 cm2/C at 535 nm and −360 cm2/C at 760 nm. The films have the advantage of exhibiting cathodic and anodic coloration. The space created by the methoxy ethylhexyloxy benzene between EDOT units on the polymer backbone makes the injection/rejection of the negatively charged counterions inside/outside of the polymer easier, resulting in higher doping levels than PEDOT at the same optical density. Very well-defined electrochemistry, high level of stability to overoxidation and long-term switching, and the chromicity properties mentioned above make P(BEDOT-MEHB) an excellent candidate for electrochromic displays.

Comparative reactivity of thiophene and 3,4-(ethylenedioxy)thiophene as terminal electropolymerizable units in bis-heterocycle arylenes

The monomers bis(2-thienyl)-9,9-didecylfluorene, BTDF, and bis(3,4-(ethylenedioxy)thien-2-yl)-9,9-didecylfluorene, BEDOT-DF, have been synthesized and electropolymerized to the corresponding conducting polymers. The potential for the electropolymerization of BTDF was found to be dependent on the solvent composition. In CH 2 Cl 2 , polymer film deposition is achieved only at potentials higher than 1.3 V vs. Ag/Ag + , while in a 30/70 mixture of CH 2 Cl 2 /CH 3 CN the polymerization is efficient at 0.9 V. BEDOT-DF polymerizes at significantly lower potentials and more rapidly than BTDF. The electron-donating alkoxy substituents of the EDOT units lead to stabilization of the cation radical intermediates allowing the electropolymerization to proceed at 0.55 V. The neutral polymers are insoluble in common organic solvents and are stable to 300°C under nitrogen. Upon oxidation, both polymers show two intragap transitions at intermediate doping levels due to the formation of bipolaronic states and the oxidized polymers exhibit conductivities up to 10 -4 S/cm. The redox-stimulated ion transport characteristics, studied by the electrochemical quartz crystal microbalance (EQCM) indicates that the electrolyte anions are the dominant mobile species.

Comparative reactivity of thiophene and 3,4‐(ethylenedioxy)thiophene as terminal electropolymerizable units in bis‐heterocycle arylenes

The monomers bis(2-thienyl)-9,9-didecylfluorene, BTDF, and bis(3,4-(ethylenedioxy)thien-2-yl)-9,9-didecylfluorene, BEDOT-DF, have been synthesized and electropolymerized to the corresponding conducting polymers. The potential for the electropolymerization of BTDF was found to be dependent on the solvent composition. In CH2Cl2, polymer film deposition is achieved only at potentials higher than 1.3 V vs. Ag/Ag+, while in a 30/70 mixture of CH2Cl2/CH3CN the polymerization is efficient at 0.9 V. BEDOT-DF polymerizes at significantly lower potentials and more rapidly than BTDF. The electron-donating alkoxy substituents of the EDOT units lead to stabilization of the cation radical intermediates allowing the electropolymerization to proceed at 0.55 V. The neutral polymers are insoluble in common organic solvents and are stable to 300°C under nitrogen. Upon oxidation, both polymers show two intragap transitions at intermediate doping levels due to the formation of bipolaronic states and the oxidized polymers exhibit conductivities up to 10−4 S/cm. The redox-stimulated ion transport characteristics, studied by the electrochemical quartz crystal microbalance (EQCM) indicates that the electrolyte anions are the dominant mobile species. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3627–3636, 1997