Polyfluorenes without Monoalkylfluorene Defects

A synthetic route to 9,9-dioctyl-9H-fluorene (free of monoalkyl-substituted fluorene defects) by alkylative cyclization of 9-biphen-2-ylheptadecan-9-ol is described. Polyfluorenes prepared by Yamamoto and Suzuki polymerization of the defect-free monomers, when incorporated in light-emitting devices, exhibited minimal green emission attributable to fluorenone formation. By contrast, devices fabricated with polyfluorene arising from conventionally synthesized 9,9-dioctyl-9H-fluorene showed significant emission at 533 nm, even at the turn-on voltage. Incorporation of as little as 0.06 mol % of 9-octyl-9H-fluorene comonomer in polyfluorene led to evolution of green fluorescence in the photoluminescence (PL) and electroluminescence (EL) emission spectra.