EDOT-dimer

Pd(OAc)2, a monodentate phosphine (P( j-tol)3 (w-tol = m-toluene)) and CS2CO3 in toluene gave high yields of dicoupled products (24-27, Scheme 19.4). This catalyst system was also applied to the biscoupling of EDOT dimers with arylbromides containing electron-rich and electron-poor groups in moderate yields (28, Chart 19.6). ... 

For the sake of simplification, only one stereoisomer of each dimeric and trimeric structure is depicted in Figure 5.10. All possible isomers are formed and can be detected by iH-NMR-spectroscopy (see Figure 5.12). The characteristic iR-NMR-spectrum of EDOT-dimer is depicted in Figure 5.13. (The spectrum shows the Id-mixture of R- and S-isomer only the formula of the S-isomer is drawn for the sake of clarity.)... 

The oxidation (dehydrogenation) of the EDOT-dimer by quinones like chloro-anil or 2,3-dichloro-4,5-dicyano-benzoquinone (see Figure 5.17) presents a rapid and easy access to the bis-EDOT (BEDOT) 2,2 -di(3,4-ethylenedioxythiophene), ... 

Although the acid-catalyzed side-reaction of EDOT to EDOT-dimers and -trimers,i induced by toluenesulfonic acid, is no dead end in the reaction route, because these intermediates are also leading to doped PEDOT at the end of the reaction (see Chapter 8), detrimental effects cannot be excluded and may be one of the reasons for improvements by the addition of bases. Additionally, catalytic effects on EDOT polymerization by protic acids— reducing pot life—are suppressed, and premature precipitation of doped PEDOT is diminished. 

As iron(III) chloride additionally functions as Lewis acid, trace amounts of the EDOT dimer and trimer (see Chapter 5) could be detected in the product iH-NMR-spectroscopically by the clearly separated peak at 5.42 ppm (o). ... 

This reaction is a side reaction, so at the end of the overall reaction, the main yield of PEDOT molecules has been formed via EDOT radical cation dimerization and a small part via dimer formation. The parameters were measured independently by experiments with toluenesulfonic acid and EDOT and the EDOT dimer, respectively. The rate constant kj for the dimer formation was found to be 1.5 x 10 L moHh" the value for the back reaction (fcg) is 1.2 X 10 LmoHh i. The oxidation rate for the dimer to BEDOT was determined to 20 LmoHh i. Here also, the trimer formation has not been taken into account the overall reaction is not influenced much by the additional trimer formation. Obviously, all reaction steps in this route to PEDOT are significantly slower than via EDOT radical cation. For a more detailed discussion of EDOT dimer and trimer formation, see Chapter 5. 

The EDOT dimerization was discussed as the reason for a remarkable catalytic effect of protons on the EDOT oxidation to PEDOT. Addition of p-toluenesulfonic acid clearly accelerafes the overall reaction, but, due to the aforementioned facts, this cannot be a result of the increased dimer (and trimer) formation effected thereby. 

In another research laboratory, surprised by the lack of success of other research groups and the previous statements about the impossibility of applying biocatalytic chemistry to polithiophenes and polypyrroles, special attention was paid to the enzymatic polymerization of the EDOT monomer [43]. In this case, the first trials succeeded and a blue-colored polymer solution was obtained after 16h of reaction (Scheme 4). As is well-known, an acidic reaction medium is suitable to increase the rate of polymerization. Protonic acids and a variety of Lewis acids catalyze the equilibrium reaction of EDOT to the corresponding dimeric and trimeric compounds without further oxidation or reaction [44]. In this work, three different pHs were evaluated (pH = 2, 4, and 6) in order to establish the optimum for adequate synthesis of EDOT. The UV-visible (UV-Vis) spectra for these three reactions are... 

Rault Berthelot, J., E. Raoult, and F. Le Floch. 2003. Synthesis and anodic oxidation of a dimer EDOT-dicyanomethylenefluorene and a truner EDOT-dicyanomethyleneflnorene-EDOT Towards mixed polymers with very low handgap. / Electroanal Chem 546 29—34. 

Similar to the previously mentioned polymers, attempts have been made toward polymerizable EDOT-based oligomers that have lower oxidation potentials than their respective monomers and longer conjugation lengths. BiEDOT (38) has an oxidation potential of 1.4 V lower than that of thiophene and 0.6 V lower than that of EDOT [139]. The dimer easily polymerizes, is air stable, and when polymerized, the resultant polymer has identical electrochromic properties to PEDOT. TerEDOT has also been synthesized with a slightly lower oxidation potential than BiEDOT. Although it is somewhat imstable and can be difficult to handle and store, it electropolymerizes to afford an electrochromic PEDOT. 

This result underlines the major impact of the sulfur atoms of the alkylsulfanyl groups on the steric distortion of the jt-conjugated chain [69]. Further work based on crystallographic, electrochemical and spectroscopic analysis of bis-EDOT, bis-EDST and mixed EDOT-EDST dimers has confirmed this fact. Whereas the solid-state structures of bis-EDOT and EDOT-EDST are planar and almost planar, respectively, bis-EDST presents a median torsion angle of 45° [70]. 

A simple, but mechanistically important feature is the ability of EDOT and a limited number of derivatives to be protonated in a-position of the thiophene ring by strong acids. The protonation—for example, performed by sulfuric acid or organic sulfonic acids, and more efficiently by trifluoro acetic acid—results in the formation of an active, electrophilic [EDOT-H]+ intermediate. Hydrochloric acid leads to additional side reactions trichloro acetic acid is far less achve than the fluoro analog. The [EDOT-H]+ is able to reversibly add to the basic C-2 of another EDOT molecule. The now formed intermediate may deprotonate to a dimeric structure, a 1,4-dihydro-thiophene derivative (see Eigure 5.10). ... 

Because the C-5 in the dimeric product in Figure 5.10 is also easily protonated, the reaction does not stop at the stage of this dimer but adds one further EDOT molecule to the trimeric structure. Due to the reversibility of all... 

The importance of dimer (and trimer) formation for basic mechanistic considerations lies in the delocalization of the positive charge- A more detailed look at the mesomeric structures of the protonated EDOT shows the massive influence of the oxygen atom(s) (Figure 5.14). 

The extension of the mesomeric system on to the oxygen atoms stabilizes the protonated EDOT and thereby facilitates dimerization and subsequent trimerization. The same stabilization is efficient in the polaronic or bipola-ronic state of FEDOT (Figure 5.15). 

Hence, the electronic reasons for the facilitation of the acid catalyzed dimerization (and trimerization) reactions of EDOT are very closely related to the prerequisites for being oxidizable to a stable conducting state, with special emphasis to the word stable in the meaning of electronically and environmentally stable. The latter means stable to air, including oxygen and humidity, and also to water and solvents like aliphatic alcohols. 

In contrast to the monomeric EDOT, protonation of all EEXDT homologs like bis-EDOT (BEDOT), ter-EE)OT, and so on, does not yield dimerization products in preparative experiments. 

The intermediate formation of dimeric and trimeric EDOT (see Figure 8.3, formulae wifhouf sfereochemical aspects) is a slow equilibrium reaction, but does not influence the overall reaction rate. For the sake of clarity, in Figure 8.2 the trimer formation has been omitted. 

Ethylenedioxythiophene (EDOT), the monomer for PEDOT, is a transparent liquid. The absorption spectrum of EDOT peaks at 260 nm. The absorption maximum shifts considerably to lower photon energy when the k system of EDOT is extended by the formation of dimers and higher oligomers in which conjugation... 

PEDOT-based hole conductors were first introduced by Saito et al. in DSSCs. The monomer EDOT or the dimer bis-EDOT was polymerized in the cell to achieve close electrical contact to the sensitizing dye. The polymerization was conducted chemically with Fe(lll) as the oxidant or photoelectro-chemically by light excitation of the dye together with an applied electrical field. Limited power efficiencies of about 2% to 3% have been achieved. Johansson et al. deposited a layer of the aqueous PEDOTPSS dispersion as a hole conductor in DSSCs and avoided the polymerization of EDOT within the device. Although only a planar, nonporous Ti02 electrode had been employed leading to a very limited light absorption the incident photon to current conversion efficiency was found to be similar to cells with the standard electrolyte as hole-transport material. ... 

Dibromobenzo-EDOT is a useful intermediate in the preparation of "trimeric" PheDOT. The analog dimeric molecule di-PheDOT is also accessible from PheDOT. The synthetic routes to the oligomeric PheDOT derivatives are summarized in Figure 13.11. ... 

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