Fluorene, iridium complex

C ]H,o, Fluorene, iridium complex 29 232 C]3H jNO, Formanide,lV-ll-(l-naphthal-enyl)ethyl]-, rhenium complex 29 217 CijHijP, Phosphine, methyldiphenyl-, iron complex 26 61, 28 171 molybdenum complex, 27 9 nickel complex, 28 101 tungsten complexes. 27 10, 28 328,28 331 CijHio, Acetylene, diphenyl-, molybdenum complex, 26 102-105, 28 11, 13 C14H12, Benzene, 1,2-ethenediylbis-, platinum complex, 26 140 C14H14, Benzene. l,l -(l,2-ethanediyl)-bis-, 26 192... 

The first efficient phosphorescent fluorene polymer was reported by Chen et al. [83], who synthesized a series of polyfluorenes containing both the triplet-emitting iridium complex and... 

These approaches have been adopted more recently to incorporate phosphorescent chromophores into PF in order to make use of the fact that a large proportion (up to 75%) of all excitons formed in LEDs are triplet states, whose energy can only be harvested by using phosphorescent units. The first fluorene copolymers with phosphorescent units 34-35 were made by Holmes and coworkers who added monobrominated red- or green-emitting iridium complexes to an AA-BB Suzuki polycondensation [57]. With short fluorene chains, only emission from the iridium complexes are observed, but with longer fluorene chains some blue emission is also seen. Other groups have since incorporated different phosphorescent units such as platinum [58] or zinc salen [59] units or porphyrins [60,61 ]. 

A problem with blending the phosphor into a matrix is that phase separation can lead to aggregation of the phosphor, which results in low phosphorescent yields. To avoid this problem, a few researchers have incorporated iridium complexes into a polymer. A few of these structures are shown in Figure 5.19. When Jiang et al. [120] mixed polymer 19 with PBD, the PPHOLEDs had an external quantum efficiency of 3.4% and a luminance efficiency of 2.9 cd/A. Holmes [164] made a series of fluorene polymers that incorporated iridium phosphors. The most efficient PPHOLEDs had an external quantum efficiency of 1.5%, which came from triplet emission and was fabricated with 20 as the active layer. These polymers prove that incorporation of the phosphors into a polymer chain can produce efficient devices and will likely be an area of further research. The CDT Web site notes that dendimers can also be used for this purpose. Dendrons can prevent the phosphorescent core from aggregating and thus, reducing PL [165]. There is little doubt that research in the arena of electrophosphorescent displays will increase in the future. 

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