title: Green emission from end-group-enhanced aggregation in polydioctylfluorene.
abstract: Green emission in polyfluorenes (PFs) has been attributed to aggregation or excimer emission, but recently it was reassigned as an on-chain fluorenone defect. We show here that, in dialkyl-substituted PFs that is hydrogen-free at the 9'-position of the fluorene, blue emission with very weak green emission is observed from end-capped polydioctylfluorene (PFO) for both photoluminescence and electroluminescence spectra, while the low-energy green emission at 507 nm is very pronounced only in uncapped PFO (PFOun). The facts that there is no detectable infrared absorption at around 1721 cm(-1) due to >C=O stretching vibration in PFOun and no charge-trapping occurring in the light-emitting device from PFOun are in contrast with those found in the literature-reported copolymers with fluorenone units, which have detectable infrared absorption at 1721 cm(-1) and charge-trapping in devices. We found that this green emission at around 507 nm originates from the end-group-enhanced aggregation by use of UV-vis absorption, photoexcitation spectra, and steady-state photoluminescent and electroluminescent spectra. The end-group-enhanced aggregation is much weaker in other PFs with less-ordered structures.
authors.affiliation: Chemical Engineering Department, National Tsing Hua University, Hsinchu, 30043, Taiwan, Republic of China.
authors.forename: Xiwen
authors.initials: X
authors.lastname: Chen
authors.forename: Hao-En
authors.initials: HE
authors.lastname: Tseng
authors.forename: Jin-Long
authors.initials: JL
authors.lastname: Liao
authors.forename: Show-An
authors.initials: SA
authors.lastname: Chen