Random terpolymers for electroluminescent devices: Synthesis and characterization of new cyano‐containing poly(fluorenylene‐vinylene)s

The synthesis of new random poly(2,7‐fluorenylene‐vinylene)s was achieved by a Suzuki–Heck cascade polymerization reaction. The poly(fluorenylene‐vinylene) base structure was modified by the regio‐random incorporation of 1‐cyano‐2,5‐phenylene as electron withdrawing unit (CN‐PFV1) and its properties were compared with terpolymers also embodying 1,4‐dioctyloxy‐2,5‐phenylene (CN‐PFV2) or 3,6‐N‐octylcarbazole (CN‐PFV3) as electron‐donating moieties. Thermal analysis revealed a high thermal stability (Td > 389 °C) and the absence of glass transitions for all polymers. Cyclic voltammetry indicated a high electron affinity of the materials (2.96–3.21 eV) attributed to the presence of the cyano‐containing comonomer. In dilute solutions, the copolymers showed a broad green fluorescence with quantum yields ranging from 0.42 to 0.79, while in the solid state, a relatively narrow emission centered at ∼ 560 nm, governed by the low‐energy segments within the π‐conjugated backbone, was observed. The electroluminescence properties of the materials were tested in OLED devices of ITO/PEDOT‐PSS/CN‐PFV1‐3/Ca/Al or ITO/PEDOT‐PSS/CN‐PFV1‐3/Alq3/Ca/Al configurations, showing a bright green‐yellow emission that, in the case of CN‐PFV2, reached 1403 cd/m2 with efficiencies as high as 0.13 cd/A.