Novel fluorene/trifluoromethylphenylene copolymers: Synthesis, spectra stability and electroluminescence

A group of novel fluorene-based copolymers were synthesized and characterized. The trifluoromethylphenylene unit was introduced into the copolymer backbone and its content ratio was varied from 10 mol% to 50 mol%. The electronic bandgap of the copolymer increases regularly with increasing trifluoromethylphenylene ratio. In contrast to pure polyfluorene, the deep-blue fluorescence of these copolymers is quite stable and not contaminated by the well-known green emission associated with fluorenone defects. The copolymers were used as an emitting layer to fabricate organic light-emitting diodes with a pure blue electroluminescence with a CIE coordinate y ≤ 0.10 obtained for most copolymers. Whilst the presence of the trifluoromethylphenylene units in the copolymers seemed unfavorable for charge injection and device current, improved spectral purity and stability in both the photoluminescence and electroluminescence were noted and ascribed to the electron-withdrawing nature of the trifluoromethylphenylene units and the enhanced anti-autoxidation ability of the fluorene rings in these copolymers.

In contrast to polyfluorene, the novel fluorene/trifluoromethylphenylene copolymers exhibit pure and stable deep-blue photoluminescence and electroluminescence, which never exhibit the undesired green emission band from keto defects.Figure optionsDownload as PowerPoint slideHighlights
► Synthesis and properties of new fluorene/trifluoromethylphenylene copolymers are described.
► Bandgap increases regularly with the content ratio of trifluoromethylphenylene unit.
► The trifluoromethylphenylene unit improves the spectral purity and stability.
► Organic light-emitting diodes are fabricated using these copolymers as emitters.
► Deep-blue electroluminescence with acceptable efficiency was obtained.