Effect of Film Morphology on the Energy Transfer to Emissive Green Defects in Dialkyl Polyfluorenes

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• 作者：Lynn J. Rozanski ; Craig W. Cone ; David P. Ostrowski ; David A. Vanden Bout
• 刊名：Macromolecules
• 出版年：2007
• 出版时间：June 26, 2007
• 年：2007
• 卷：40
• 期：13
• 页码：4524 - 4529
• 全文大小：145K
• 年卷期：v.40,no.13(June 26, 2007)
• ISSN：1520-5835

文摘

The formation of a ketone defect at the 9-site along the backbone of dialkyl polyfluorenes hasbeen shown to be directly involved in the degradation of the polymer's emission from blue to an undesirablegreen. Films of poly(9,9'-dihexylfluorene) (PFH) with and without ketone defects were annealed above theirliquid crystalline phase transition in an inert argon atmosphere, and their emission spectra were collected in orderto study the effect of morphology on the energy transfer to ketone defects. The annealing was performed in situin the fluorometer, allowing for a direct comparison of the absolute changes in the emission spectra. Annealingof the films resulted in regions of highly aligned polymer chains as confirmed by atomic force microscopy. Afterannealing, the fluorescence spectra of pristine films (without ketone defects) exhibited no green emission, indicatingthe lack of thermal oxidation in the inert atmosphere. However, these films did show an increase in fluorescencequantum yield, revealing that high polymer order does not lead to interchain electronic species that quench theexcited states. Annealing of partially photobleached PFH films revealed that an increase in the polymer chainorder of a film containing a few defects resulted in an increase in green emission and decrease in blue withoutthe creation of further defects. The increase in green emission combined with the decreased blue can only be theresult of increased energy transfer from pristine chromophores to ketone sites, as the aligned polymer chainsincrease exciton diffusion. PFH films containing defects that were annealed beneath the LC temperature of thepolymer did not result in any spectral changes, indicating that alignment of polymer chains was necessary for theincreased energy transfer to the defect sites.