Doped Polymers by Oxidative Polymerization. 4. Oxidative Coupling of Methylated Oligothiophenes by FeCl₃·6H₂O as a Model Reaction for the Oxidative Polymerization of Thiophene Derivatives

Abstract

Methylated bi- and terthiophenes (monomers, 1, 3, 5, 8) with one free α-position can be oxidized with FeCl3·6H2O. An irreversible dimerization reaction forms dimers of the expected structure. The radical cations of the monomers also react with free β-positions of the formed dimers (6, 9) having two methylated α-positions. The products of these reactions show α,β‘ linkages (7, 10, 11). Different β-positions in end-capped dimers show a graduated reactivity against radical cations of the monomers; the free β-position with the higher electron spin density can be attacked preferably by an α-position of a radical cation of a monomer molecule. No products with β,β‘ linkages were found. Electrochemical investigations using fast-scan voltammetry show the formation of α,α‘ linkages of methylated oligothiophenes. For bithiophene derivatives, rate constants of the dimerization process in the range of 109 L·mol-1·s-1 were determined. In comparison with a terthiophene derivative, it was found that the dimerization rates decrease with increasing chain length of the oligomers.

The synthesis and electrochemistry of 2,5-dimethylazaferrocenes with heteroaryl bridges

“…Obviously, oxidized 12 electropolymerizes rapidly. This is a well-known behavior of thiophenes [20][21][22].…”

Organic Semiconductors for Solution‐Processable Field‐Effect Transistors (OFETs)

“…The oldest method is the oxidative coupling of two shorter oligothiophenes with iron(III) chloride. [22] The Scheme 5. Synthesis of acene-thiophene "hybrid compounds" (the final elimination of the TMS group is not shown).…”

Optimization of direct arylation polymerization (DArP) through the identification and control of defects in polymer structure

“…since all the corresponding monomers in those cases have only one reactive nucleophilic functionality, which leads to linear polymer primary structure [Scheme (b)]. However, the precedent for β‐defect formation has been reported for the case of oxidatively polymerized polythiophenes (e.g., using FeCl 3 as an oxidant) although in that case the mechanism of polymerization is entirely different …”