Syntheses and properties of small-bandgap liquid crystalline conjugated polymers

We present syntheses and properties of thermotropic liquid crystalline conducting polymers with small-bandgaps. The polymers consist of aromatic and quinoid units in the polymer backbone and a methine-bridge substituted with a liquid crystalline group. We adopted a thienylene or pyrrolylene ring as a heteroarylene unit and a phenylcyclohexyl moiety as a mesogenic core in the liquid crystalline group. The thienylene-based polymers exhibited smectic E or smectic A phases. The bandgaps evaluated for these polymers were 1.45 similar to 1.54 eV and 2.48 eV, depending on an intramolecular pi-electron resonance interaction between the main chain and the liquid crystalline side chain.