Single-molecule electroluminescence and photoluminescence of polyfluorene unveils the photophysics behind the green emission band
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AbstractOptoelectronic 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. © 2014 Macmillan Publishers Limited. All rights reserved.
CitationHonmou, Y., Hirata, S., Komiyama, H., Hiyoshi, J., Kawauchi, S., Iyoda, T., & Vacha, M. (2014). Single-molecule electroluminescence and photoluminescence of polyfluorene unveils the photophysics behind the green emission band. Nature Communications, 5(1). doi:10.1038/ncomms5666
SponsorsBan Xuan Dong and Dr Satoshi Habuchi (currently at KAUST, Saudi Arabia) were present during the early stages of the research and their contributions as well as discussions are gratefully acknowledged. Dr Shingo Hadano is acknowledged for invaluable assistance in the synthesis of the BC and polyfluorene. Tatsuya Ishii and Shoki Matsuda helped with the analysis of the single-molecule PL spectra. The work was supported by Grants-in-Aid for Scientific Research No. 23651107 and 26287097 of the Japan Society for the Promotion of Science. The numerical calculations were carried out on the TSUBAME 2.0 supercomputer in the Tokyo Institute of Technology, Tokyo, Japan and on the supercomputer in the Research Center for Computational Science, Okazaki, Japan.
PublisherSpringer Science and Business Media LLC