Synthesis and electroluminescent properties of cyclohexyl-substituted polyfluorenes

To lessen the excimer formation often observed in many poly(dialkylfluorene) derivatives, various lengths of alkyl chains containing bulky cyclohexyl groups were substituted to polyfluorenes at the C-9 position. Three polymers were synthesized by Ni(0)-mediated polymerization. PF1CY has very poor solubility because of the rigidness of the backbone caused by the closely lying bulky cyclohexyl substituents, and therefore the soluble fraction showed oligomeric properties. PF4CY displayed green electroluminescence (EL) of an excimer emission; insulation of backbones by such a length of substituents is not effective enough to prevent the excimer formation. However, PF7CY was able to suppress excimer formation by effective aggregation. Efficient blue EL was obtainable with PF7CY.