Processible conjugated polymers: from organic semiconductors to organic metals and superconductors

Since conjugated polymers, i.e. polymers with spatially extended pi -bonding system offer unique physical properties, unobtainable for conventional polymers, significant research efforts directed to better understanding of their chemistry, physics and engineering have been undertaken in the past two and half decades. In this paper we critically discuss synthetic routes to principal conjugated polymers such as poly(acetylene), polyheterocyclic polymers, poly(p-phenylene vinylene)s, aromatic poly(azomethine)s and poly(aniline) with special emphasis on the preparation of solution (and in some cases thermally) processible polyconjugated systems. In their neutral (undoped) form conjugated polymers are semiconductors and can be used as active components of 'plastics electronics' such as polymer light-emitting diodes, polymer lasers, photovoltaic cells, field-effect transistors, etc. Due to its strongly non-linear I = f(V) characteristics in high electric fields, undoped poly(aniline) can be used as stress grading material for high voltage cables. In the next part of the paper we describe redox and acid-base doping of conjugated polymers and its consequences on structural, spectroscopic and electrical transport properties of these materials. Special emphasis is put on dopant engineering, i.e. on the design of the dopants which not only increase electronic conductivity of the polymer but also induce desired properties of the doped polymer system such as improved processibility, special catalytic properties or special optical or spectroscopic properties. Selected examples of technological applications of doped conjugated polymers are presented such as their use as conductive plastics, optical pH sensors, heterogeneous catalysts, gas separation membranes, etc. The paper is completed by the description of the recent discovery of the first organic polymer superconductor. (C) 2001 Elsevier Science Ltd. All rights reserved.