Electronic processes in liquids of aromatic and conjugated structure

Organic liquids and polymer liquids with highly extended /spl pi/-conjugated electron system in their structures have much smaller band gaps than those of conventional dielectric liquids and therefore exhibit relatively high electrical conductivity and interact with visible light. In these liquids, various anomalous temperature dependences were observed in electrical conductivity, photoconductivity and photoluminescence, which have been discussed in terms of changes of electronic energy states and the inter-chain interaction with temperature. The band gap in the liquid state is found to be larger than in the solid state and fluctuates in the pre-melting region. The top of valence band (HOMO level) in the liquid state is found to be lower in energy than that in the solid state except for poly(3-alkylthiophene) of long alkyl side chains by the measurement of photo-electron emission. Polarity effects of photoconductivity indicates major role of electrons in the liquid state but both electrons and holes play roles in the pre-melting region. Electroluminescence has been studied in these /spl pi/-conjugated organic liquids and polymers. Novel characteristics of these /spl pi/-conjugated organic molecules and polymers in various solvents such as thermochromism and electro-rheology (voltage dependent viscosity) have also been observed. Unique phenomena at conducting polymer-electrode and conducting polymer-dielectric liquids interfaces have also been studied.