Poly-(p-phenylene vinylenes) with pendent 2,4-difluorophenyl and fluorenyl moieties: Synthesis, characterization, and device performance

To improve efficiency, processability, and stability, three novel poly-(p- phenylene vinylenes) (PPVs) derivatives (P_a, P_b, and P_c) with pendent 2,4-difluoro- phenyl and fluorenyl moieties were synthesized via Gilch reaction. Their structures were characterized by 1H NMR, 13C NMR, and Elem.Anal. Compared with those of PPV and MEH-PPV, the absolute quantum efficiencies of these polymers showed remarkable improvement (measured at 38.7, 37.2, and 20.3%, respectively), which can be attributed to the presence of twisted multiaryl segments and fluorine atoms. TGA revealed that the inflection temperatures of their thermal decomposition curves were above 400 °C. Double-layered electroluminescent devices with these polymers as light-emitting layers [ITO/PEDOT:PSS/Polymer/Ba/Al] showed peak emissions at 493/515, 503, and 600 nm and maximum luminance of 2700, 450, and 4700 cd/m2 for P_a, P_b, and P_c, respectively, with onset voltages of ∼ 4V.