Partially oxidized poly thiophenes

A major reason for the failure of poly(acetylene)s in the above-mentioned applications is related to their inherent instability versus moisture and oxygen, and their high susceptibility to decomposition/rearrangement in the partially oxidized/doped state. Nevertheless, poly(ene)s stabilized by appropriate ligand systems and/or incorporated into cyclic structures are believed to exhibit similar stabilities to poly(thiophene)s, poly(pyrrole)s, poly(p-phenylene)s, PPV, and so on. In the following, we will outline the basic concepts of poly(ene)s as well as reviewing the structures that have been realized so far. 

Poly[3-(ethylmercapto)thiophene] and poly[3,4-bis-(ethylmercapto)thiophene] were prepared by Grignard coupling of the corresponding diiodide [95]. These polymers were soluble in common organic solvents such as methylene chloride, chloroform and tetrahydrofuran and their Dp was 15-20. Visible-near IR spectra of electrochemically doped film and chemically doped solution of the polymers showed that they could be oxidized to form bipolaronic species. The polymers showed three to six orders of magnitude lower conductivity than poly(3-alkylthiophene). One possible explanation for this was partial positive charge localization onto the sulfur atom of the ethylmercapto substituent. 

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