Poly(fluorenevinylene) derivatives by Heck coupling: Synthesis, photophysics, and electroluminescence

Three new poly(fluorenevinylene) derivatives were synthesized, characterized, and used as emissive materials in light‐emitting diodes (LEDs). They were synthesized by Heck coupling of 9,9‐dihexyl‐2,7‐divinylfluorene with 2,7‐dibromo‐9,9‐dihexylfluorene, 2,3‐bis(4‐bromophenyl)quinoxaline, or 2,5‐bis(4‐bromophenyl)‐3,4‐diphenylthiophene to afford the polymers F, Q, and T, respectively. Polymers F and Q had medium number–average molecular weights (Mn ˜ 14,000) with relatively narrow polydispersity (1.3–1.6), while T was obtained as an oligomer (Mn ˜ 4000). All polymers were soluble in common organic solvents, such as tetrahydrofuran (THF), chloroform, dichloromethane, and toluene. They emitted blue‐greenish fluorescence light in dilute THF solution (444–491 nm), with photoluminescence (PL) quantum yields of 0.32–0.54, and in thin film (453–488 nm). LEDs with the configuration of ITO/PEDOT‐PSS/Polymer/Li:Al were fabricated and evaluated. The electroluminescence (EL) spectra of the Q and F polymers were very broad covering the blue–green–red region, whereas the spectrum of the polymer T was almost purely blue. The threshold electrical field for light emission of the devices was almost the same (˜1.75 MV/cm). The external quantum efficiency of the devices of polymers Q and F was about 1.0 × 10−3%, whereas that of polymer T was ˜3.0 × 10−5%. The fluorescence lifetime of polymers F and Q was significantly longer than that of the polymer T.