Abstract
We propose a simple way to achieve pure blue emission and improved device efficiency via capping poly(9,9-dioctylfluorene) (PFO) with electron-deficient moieties (EDMs, such as oxadiazole (OXD) and triazole (TAZ)), which can induce minor amount of long conjugating length species (regarded as β phase) to control extents of energy transfer from amorphous matrix to the β phase. The device efficiency of PFO end-capped with TAZ is higher than that with para-tert-butyl phenyl (TBP) by a factor of two (with CsF/Al as cathode), and its electroluminescent (EL) spectrum remains stable and pure blue emission during cyclic operations (C.I.E. color coordinates x = 0.165, y = 0.076, independent of operating voltage and within the limit for pure blue emission x + y < 0.30). The improvement of device efficiency is dependent on the structure of EDM such as size and planarity. The deep blue emission is originated from the incomplete energy transfer from amorphous matrix to β phase induced by the end-cappers.