THE ROUTES TOWARDS PROCESSIBLE AND STABLE CONDUCTING POLY(THIOPHENE)S

The underlying nature of the thermal instability of doped poly(3-alkyl thiophene)s, a fatal problem for their application, is discussed. The so-called ''thermal undoping'' is attributed to interactions due to st eric hindrance of the long flexible side chains, which twist the conju gated main chain and kick out the dopants. Thus the routes to suppress thermal undoping are to avoid or alleviate the side chain interaction s by separating the side chains from each other, or from the main chai ns, and also leaving space around the main chains to accommodate dopan ts. Accordingly, poly(3-(4-octylphenyl)thiophene), random copolymers o f 3-methylthiophene and 3-octylthiophene, and regular copolymers of th iophene and 3-octylthiophene are prepared. Thermal undoping is signifi cantly suppressed in these polymers. Some of these polymers are solubl e and fusible in the neutral state. After doping they become highly co nductive, yet remain stable even at elevated temperatures. Thermochrom ism, solvatochromism and thermal undoping are thus all related to side chain mobility.