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We have synthesized a blue-light-emitting polyfluorene (PF) derivative (PF-CBZ-OXD) that presents bulky hole-transporting carbazole and electron-transporting oxadiazole pendent groups functionalized at the C-9 positions of alternating fluorene units. The results from photoluminescence and electrochemical measurements indicate that both the side chains and the PF main chain retain their own electronic characteristics in the copolymer. An electroluminescent device incorporating this polymer as the emitting layer was turned on at 4.5 V; it exhibited a stable blue emission with a maximum external quantum efficiency of 1.1%. Moreover, we doped PF-CBZ-OXD and its analogue PF-TPA-OXD with a red-light-emitting iridium phosphor for use as components of phosphorescent red-light emitters to investigate the effect of the host's HOMO energy level on the degree of charge trapping and on the electrophosphorescent efficiency. We found that spectral overlap and individual energy level matching between the host and guest were both crucial features affecting the performance of the electroluminescence devices. Atomic force microscopy measurements indicated that the dipolar nature of PF-CBZ-OXD, in contrast to the general nonpolarity of polydialkylfluorenes, provided a stabilizing environment that allowed homogeneous dispersion of the polar iridium triplet dopant. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2925–2937, 2007

We have developed efficient white-light-emitting polymers through the incorporation of low-bandgap orange-light-emitting benzoselenadiazole (BSeD) moieties into the backbone of a blue-light-emitting bipolar polyfluorene (PF) copolymer, which contains hole-transporting triphenylamine and electron-transporting oxadiazole pendent groups. By carefully controlling the concentrations of the low-energy-emitting species in the resulting copolymers, partial energy transfer from the blue-fluorescent PF backbone to the orange-fluorescent segments led to a single polymer emitting white light and exhibiting two balanced blue and orange emissions simultaneously. Efficient polymer light-emitting devices prepared using this copolymer exhibited luminance efficiencies as high as 4.1 cd/A with color coordinates (0.30, 0.36) located in the white-light region. Moreover, the color coordinates remained almost unchanged over a range of operating potentials. A mechanistic study revealed that energy transfer from the PF backbone to the low-bandgap segments, rather than charge trapping, was the main operating process involved in the electroluminescence process. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2938–2946, 2007

We have synthesized a blue-light-emitting polyfluorene derivative (PF-TPAOXD) that presents sterically hindered, dipolar pendent groups functionalized at the C-9 positions of alternating fluorene units. The incorporation of the dipolar side chains, each comprising an electron-rich triphenylamine group and an electron-deficient oxadiazole group connected through a π-conjugated bridge, endows the resultant polymer with higher highest occupied molecular orbital and lower lowest unoccupied molecular orbital energy levels, which, consequently, lead to an increase in both hole and electron affinities. An electroluminescent device incorporating this polymer as the emitting layer exhibited a stable blue emission with a maximum brightness of 2080 cd/ m 2 at 12 V and a maximum external quantum efficiency of 1.4% at a brightness of 137 cd/m 2 . Furthermore, atomic force microscopy measurements indicated that the dipolar nature of PF-TPAOXD, in contrast to the general nonpolarity of polydialkylfluorenes, provided a stabilizing environment allowing the polar organometallic triplet dopant to be dispersed homogeneously. We also fabricated an electrophosphorescent device incorporating PF-TPAOXD as the host material doped with a red-emitting osmium complex to realize red electroluminescence with Commission Internationale de l'Eclairage color coordinates of (0.66, 0.34). The resulting device exhibited a maximum external quantum efficiency of 7.3% at a brightness of 1747 cd/m 2 and a maximum brightness of 7244 cd/ m 2 .