title: Single-molecule electroluminescence and photoluminescence of polyfluorene unveils the photophysics behind the green emission band.
abstract: Optoelectronic properties of polyfluorene, a blue light-emitting organic semiconductor, are often degraded by the presence of green emission that originates mainly from oxidation of the polymer. Here, we use single-molecule electroluminescence (EL) and photoluminescence (PL) spectroscopy on polyfluorene chains confined in vertical cylinders of a phase-separated block copolymer to spectrally resolve the green band and investigate in detail the photophysical processes responsible for its appearance. In both EL and PL, a substantial fraction of polyfluorene chains shows spectrally stable green emission which is ascribed to a keto defect. In addition, in EL, we observe a new type of vibrationally resolved spectra distributed over a wide range of frequencies and showing strong spectral dynamics. Based on quantum chemical calculations, this type is proposed to originate from charge-assisted formation and stabilization of ground-state aggregates. The results are expected to have broad implications in the fields of photophysics and material design of polyfluorene materials.
authors.affiliation: Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Ookayama 2-12-1-S8, Meguro-ku, Tokyo 152-8552, Japan.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Honmou
authors.affiliation: Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Ookayama 2-12-1-S8, Meguro-ku, Tokyo 152-8552, Japan.
authors.forename: Shuzo
authors.initials: S
authors.lastname: Hirata
authors.affiliation: Chemical Resources Laboratory, Tokyo Institute of Technology, Nagatsuta-cho 4259, Midori-ku, Yokohama 226-8503, Japan.
authors.forename: Hideaki
authors.initials: H
authors.lastname: Komiyama
authors.affiliation: Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Ookayama 2-12-1-S8, Meguro-ku, Tokyo 152-8552, Japan.
authors.forename: Junya
authors.initials: J
authors.lastname: Hiyoshi
authors.affiliation: Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Ookayama 2-12-1-S8, Meguro-ku, Tokyo 152-8552, Japan.
authors.forename: Susumu
authors.initials: S
authors.lastname: Kawauchi
authors.affiliation: Chemical Resources Laboratory, Tokyo Institute of Technology, Nagatsuta-cho 4259, Midori-ku, Yokohama 226-8503, Japan.
authors.forename: Tomokazu
authors.initials: T
authors.lastname: Iyoda
authors.affiliation: Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Ookayama 2-12-1-S8, Meguro-ku, Tokyo 152-8552, Japan.
authors.forename: Martin
authors.initials: M
authors.lastname: Vacha