Synthesis and Characterization of Blue-Light-Emitting Alternating Copolymers of 9,9-Dihexylfluorene and 9-Arylcarbazole

Several soluble and well-defined copolymers of 9,9-dihexyl-2,7-fluorene and 9-aryl-3,6-carbazole (aryl = phenyl, p-methylphenyl, p-methoxyphenyl) were prepared in good yields by Suzuki-type coupling polymerization of fluorene−diboronic ester with some 9-aryl-3,6-dibromocarbazole derivatives. These copolymers showed high glass transition temperatures, and their regiochemical structures and physical properties were studied by gel permeation chromatography, NMR, UV absorption, elemental analysis, thermogravimetry, photoluminescence, and quantum yield measurements. The influence of the carbazole core and its aryl substituent on the photophysical, electrochemical, and electroluminescent properties of these alternating fluorene/carbazole copolymers has been investigated. Both the absorption and photoluminescence peaks of these copolymers are blue-shifted relative to the poly(9,9-dihexylfluorene) homopolymer (PF - C 6), and cyclic voltammetry showed that these copolymers have their HOMO energy levels raised relative to that of PF - C 6, thus facilitating hole injection into the copolymers from the indium tin oxide (ITO) anode. The copolymers exhibited very good thermal stability and blue emission in both solution and the solid state. Unlike PF-C 6, these copolymers showed high photoluminescent stability toward annealing action under vacuum. Blue electroluminescence with negligible low-energy emission bands was successfully achieved from these copolymers by using bathocuproine (BCP) as a hole-blocking layer and aluminum tris(8-hydroxyquinoline) (Alq3) as an electron-injection/transporting layer.