Synthesis and characterization of new red-emitting polyfluorene derivatives containing electron-deficient 2-pyran-4-ylidene-malononitrile moieties

Article abstract of DOI:10.1021/ma0355397

A novel series of red-light-emitting copolymers derived from fluorene and 2-pyran-4-ylidene-malononitrile (PM) have been synthesized through a palladium-catalyzed Suzuki coupling reaction. The polymers were characterized by FT-IR, NMR, and elemental analysis. All these polymers are completely soluble in common organic solvents, such as THF, CH₂Cl₂, CHCl₃, and toluene, and they have good thermal stability with onset decomposition temperature (T_d) of 406-407°C and glass-transition temperature (T_g) of 73-186°C. Cyclic voltammetry studies reveal that these copolymers have low-lying LUMO energy levels ranging from -3.53 to -3.57 eV and HOMO energy levels ranging from -5.77 to -5.79 eV, which indicated that they may be promising candidates for electron-transporting or hole-blocking materials in light-emitting diodes. These polymers in thin films can emit strong red photoluminescence (PL) around 641-662 nm with the corresponding additional peaks in the range 704-712 nm upon photoexcitation. Double-layer LEDs fabricated with the configuration of ITO/PEDOT/polymer/Ba/Al can emit red light with external quantum efficiencies of 0.21-0.38%. Preliminary electroluminescent (EL) results show that these polymers are novel promising candidates for red emissive materials in polymer light-emitting diodes.