Emission properties of pristine and oxidatively degraded polyfluorene type polymers

We present a detailed and comprehensive picture of the photophysics including device applications within the polyfluorene family of conjugated polymers. First, the photophysics of pristine polyfluorenes in solution and film is outlined, including a discussion of the so-called β-phase, which is characterised by a more planar ground state configuration. Particular attention is also dedicated to the occurence of low energy emission bands, which often deteriorate the initially blue emission of polyfluorenes, especially in electroluminescent devices. Although the origin of these emission features has been the object of a controversial discussion, strong evidence for our current ascription to emissive on-chain fluorenone defects is given also in contrast to previous assignments to aggregates, excimers, or exciplexes. According to the current attribution fluorenone-containing polyfluorenes can be described as a guest host system. Following this picture the photoexcitation dynamics from the fs to the ms regime is outlined. Finally, polymer light emitting diodes (PLEDs) based on polyfluorene-type emitters are discussed, especially related to their degradation mechanisms and possible remedies provided by chemistry to reduce the oxidative degradation of polyfluorene-based PLEDs. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)