Fine tuning the purity of blue emission from polydioctylfluorene by end-capping with electron-deficient moieties.
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 a minor amount of long conjugating length species (regarded as beta phase) to control extents of energy transfer from amorphous matrix to the beta phase. The device efficiency of PFO end-capped with TAZ is higher than that with para-tert-butyl phenyl (TBP) by a factor of 2 (with CsF/Al as cathode), and its electroluminescent spectrum remains stable and with 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 the beta phase induced by the end-cappers.
Hung
Ming-Chin
MC
Chemical Engineering Department, National Tsing-Hua University, Hsinchu 30041, Taiwan, Republic of China.
Liao
Jin-Long
JL
Chen
Show-An
SA
Chen
Su-Hua
SH
Su
An-Chung
AC
D005449:Fluorenes / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000737:chemistry*; D015394:Molecular Structure; D014230:Triazoles / Q000737:chemistry
D005449:Fluorenes; D005456:Fluorescent Dyes; D014230:Triazoles