Random terpolymers for electro luminescent 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(fluorenylenevinylene) 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 re-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/m 2 with efficiencies as high as 0.13 cd/A.