Liquid Crystalline Polythiophene Bearing Phenylnaphthalene Side-Chain

Polythiophene bearing a 2-phenylnaphthalene side group at 3-position was synthesized from a 2,5-dibromothiophene monomer by two polymerization methods, i.e., Yamamoto dehalogenative polycondensation using Ni(cod)2 and Ni-catalyzed chain-growth polymerization. Polymers prepared by the former method had good solubility for organic solvents, 6300–8400 g mol–1 of number-average molecular weights, absorption bands at around 300 and 385 nm due to π–π* transitions at the phenylnaphthalene moiety and polythiophene backbone, a main fluorescence emission band at around 540 nm from the polythiophene backbone in solution and film state, and presence of enantiotropic liquid crystalline phases which enabled to construct an arrayed state. On the other hand, the latter polymer showed considerably red-shifted absorption and emission bands at around 444 and 585 nm in solution and 509 and 720 nm in film state respectively, but had poor solubility and unresolved mesophases.