Synthesis and light-emitting properties of fluorene-based copolymers: Bearing diphenyl imidazole chromophore

New type of alternating fluorene-based copolymers containing electron-deficient aryl-substituted imidazole units in the main chains were designed, synthesized and characterized. The resulting copolymers were amorphous and showed excellent solubility in common organic solvents, such as dichloromethane, chloroform, 1,2-dichloroethane, chlorobenzene, toluene, and THF. These polymers also possessed good thermal stability with glass transition temperatures of 96 and 82 °C and decomposition onset temperatures of 365 and 379 °C, respectively. They exhibited good blue photoluminescence properties with high photoluminescence efficiencies. The long-wavelength emission of polyfluorenes had been effectively reduced by introduction of nonlinear structure aryl-substituted imidazole units. Light-emitting devices with an ITO/PEDOT/PVK/copolymer/LiF/Al configuration could emit strong blue light with high external quantum efficiencies of 1.49 and 2.05%.