Electroluminescence of the d-transition metal enolates

The nature of Dexter triplet energy transfer between bonded systems of a red phosphorescent Ir + complex and a conjugated polymer, polyfluorene, has been investigated in electrophosphorescence OLEDs . Red-emitting phosphorescence has been described based on the [Ir(btp)2(acac)j fragment attached either directly (spacerless) or through a —(CH2)8— chain (octamethylene-tethered) at the 9-position of a 9-octylfluorene host. Xu and coworkers reported that an efficient red EP with CIE chromaticity coordinates X = 0.69, y = 0.29, independent on current density, was obtained from [Ir(acac)(btfmp)2] doped devices. The EL spectrum has a maximum at 648 nm. A maximum external quantum efficiency of 9.6%, at current density of 0.125 mAcm, and a maximum luminance of 4200 cdm , at 7 = 552 mAcm , have been obtained. 

Three iridium complexes of formula [Ir(acac)(L)2] have been synthesized, [k(dpp)2 (acac)], [Ir(bpp)2(acac)j and [Ir(fpp)2(acac)j, where L is a substituted arylpyridine (dpp = 2,4-diphenylpyridine bpp = 2-(4-f-butylphenyl)-4-phenylpyridine fpp = 2-(4-fluoroph-enyl)-4-phenylpyridine). The OLEDs based on these materials, with structure ito/Ir com-plexipvk/F-tbb/Alqs/LiF/Al (F-tbb = l,3,5-tris(4-fiuorobiphenyl-4 -yl)benzene), showed maximum luminances of 8776, 8838 and 14180 cdm , and maximum external efficiencies of 11.5, 12.9 and 17.0 cdA, repectively ° . 

Polymer light-emitting devices (PLEDs) have attracted considerable interest because of their potential use in portable electronic devices. PLEDs have improved the performance of devices by increasing the device stability and efficiency. Chang and coworkers fabricated an efficient PLED using [Ir(acac)(dbq)2] as the phosphorescent dopant of a pvk matrix layer and bbpo as the electron transport material. Trapping of charge carriers at the [Ir(acac)(dbq)2] dopant sites dominates the EL of the device. This is the first PLED that emits red electrophosphorescence centered at 610 nm, exclusively from the dopant and an EL efficiency of 8.5 cdA (luminance 1287 cdm ) biased at 14.5 mAcm .  

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