Electrochemical synthesis of highly conducting poly(thiophene) thin films

The electrical conductivity of poly(3-methyl-thiophene) (PMeT) thin films has been investigated at various stages of the electropolymerization reaction. It is shown that the polymer growth is accompanied with a steady decrease of the conductivity. As a consequence, when the polymerization is limited to very thin films, conductivities up to 2 10³ S cm^-1 can be obtained in optimal conditions. A parallel analysis of the spectroscopic properties of the polymer reveals a bathochromic shift of the absorption maximum as film thickness is decreased, indicating that the mean conjugation length is noticeably more extended in ultrathin films. These results underline the relationships between the macroscopic and the molecular structure of the polymer and they show that both are subject to an increasing disorder as the electropolymerization proceeds.