Perfluorinated polymer with unexpectedly efficient deep blue electroluminescence for full-colour OLED displays and light therapy applications

The fluorinated phenylene unit is used as a building block for an all-conjugated fluorene-based alternating copolymer (PFO-TFP). The synthesis, carried out by an optimized Suzuki cross-coupling, produces an extremely high purity compound with a series of intriguing properties. Firstly, a blue-shift of the absorption and emission spectra with respect to the parent polymer is achieved. Secondly, the photoluminescence (PL) quantum yields (QYs) of the solution, as high as 68%, are surprisingly retained in the solid-state. Finally, an improved colour stability of the film with respect to unsubstituted polymers, investigated by means of cyclic voltammetry and exposure to ultraviolet radiation, is observed. The PFO-TFP tested as an undoped active layer in a polymer light-emitting diode (PLED) shows a highly desirable pure deep blue 405 nm electroluminescence, CIE = (0.17; 0.06) and a remarkable 5.03% external quantum efficiency, thus fulfilling the requirements for both full-colour displays and biomedical applications. To date, fluorine atom incorporation has been successfully employed in the synthesis of high-performing polymers for organic field-effect transistors and photovoltaics. We give the first unambiguous proof of its efficacy in achieving pure deep blue electroluminescence in a highly efficient and stable PLED, which is competitive with the best reported conjugated oligomer-based devices.