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The Influence of UV Irradiation on Ketonic Defect Emission in Fluorene‐Based Copolymers
Author(s) -
Scheiber Horst,
Graf Michael,
Plank Harald,
Zojer Egbert,
Slugovc Christian,
Kappaun Stefan,
Galbrecht Frank,
Scherf Ullrich,
List Emil J. W.
Publication year - 2008
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.200800389
Subject(s) - materials science , irradiation , fourier transform infrared spectroscopy , photoluminescence , photochemistry , fluorene , fluorenone , polymer , oled , absorption (acoustics) , spectroscopy , absorption spectroscopy , infrared , optoelectronics , layer (electronics) , chemical engineering , optics , nanotechnology , chemistry , composite material , physics , quantum mechanics , nuclear physics , engineering
Abstract The influence of UV irradiation in inert atmosphere on the emission spectrum of fluorenone containing poly[9,9‐bis(2‐ethyl)hexylfluorene] (PF2/6) has been investigated by means of optical absorption, photoluminescence (PL) and Fourier transform infrared (FTIR) spectroscopy. It is shown that a substantial reduction of green emission arising from ketonic defect sites can be achieved by irradiation of thin films with UV light. This is found to be accompanied by partial cross‐linking of the films. FTIR measurements show no reduction of the C=O stretching mode upon irradiation, and, moreover, the degree of cross‐linking does not scale with the relative fluorenone content (0.1, 0.5, and 5%). Therefore, the reduced emission intensity in the green spectral region is rather associated with the occurrence of interruptions in the polymer backbone, which reduce the effective conjugation length and subsequently inhibit the energy transfer onto the ketonic defect sites. The found results enabled us to build organic light emitting devices (OLEDs) that can be structured by selective illumination of the emitting layer with an intense UV light source. This method allows for the fabrication of rather efficient (2000 cd m −2 at 7 V) two‐color OLEDs.