Synthesis and optical and electrochemical properties of copolymers consisting of 9,9-dihexylfluorene and aromatic triazole chromophores

Aromatic triazole chromophores were incorporated into polyfluorene in an attempt to increase electron affinity, to promote emission efficiency, and to diminish excimer formation. Poly(9,9-dihexylfluorene) (P1) and new copolymers with aromatic triazoles (P2-P4) were prepared by Suzuki coupling polymerization. In P2, the aromatic triazole (3.8 mol %) was attached exclusively as terminal groups, whereas P3 and P4 were main-chain copolymers containing 3.9 and 10.3 mol % aromatic triazole chromophores, respectively. The copolymers were soluble in common organic solvents and showed high decomposition temperatures (437-458 degrees C). The twisted structure between the triazole and fluorene increased the emission efficiency and effectively prevented excimer formation in P2-P4. After the introduction of the triazole units, the absorption spectra showed a blueshift (from 388 to 381 nm in chloroform) due to confined conjugation, but the photoluminescence spectra remained almost the same (417-418 nm); this was attributed to oligofluorene segments. No emission of triazole fluorophores was observed because of efficient energy transfer from the triazole to oligofluorene segments. However, incomplete energy transfer was observed in CH3COOH. The optical stability upon thermal annealing was also improved by the incorporation of aromatic triazole segments. From cyclic voltammetry results, P2-P4, containing triazole groups, showed greater electron affinity (lowest unoccupied molecular orbital level - -2.67 to -2.71 eV) than P1 (-2.52 eV). Electroluminescence devices of Pl-P4 all exhibited excimer emissions (483-521 nm), which could also be diminished by the introduction of aromatic triazole chromophores. (c) 2006 Wiley Periodicals, Inc.