We demonstrate that three Ir͑III͒ complexes used as principal dopants in organic electrophosphorescent diodes have very high photoluminescence quantum efficiency ͑ PL ͒ in a solid-state film. The green emitting complex, fac-tris͑2-phenylpyridinato͒iridium͑III͒ ͓Ir͑ppy͒ 3 ͔, the red-emitting bis͓2-͑2Ј-benzothienyl͒pyridinato-N , C 3 Ј͔ ͑acetylacetonato͒iridium͑III͒ ͓Btp 2 Ir͑acac͔͒, and the blue complex bis͓͑4 , 6-difluorophenyl͒pyridinato-N , C 2 ͔͑picolinato͒iridium͑III͒ ͑FIrpic͒ were prepared as codeposited films of varying concentration with 4,4 Ј-bis͑N-carbazolyl͒-2 , 2 Ј-biphenyl, a commonly used host material. The maximum PL values for Ir͑ppy͒ 3 , Btp 2 Ir͑acac͒, and FIrpic were, respectively, 97% ± 2% ͑at 1.5 mol%͒, 51% ±1% ͑at 1.4 mol%͒, and 78% ± 1% ͑at 15 mol%͒. Furthermore, we also observed that the maximum PL of FIrpic reached 99% ± 1% when doped into the high triplet energy host, m-bis͑N-carbazolyl͒benzene, at an optimal concentration of 1.2 mol%.
Solid-state self-quenching processes of highly efficient Ir(III) phosphorescent emitters are investigated by the measurement of thin film photoluminescence quantum efficiency and transient lifetime as a function of doping concentration in a host matrix. The radiative decay rate constant is found to be independent from the average distance between dopant molecules (R), and the concentration-quenching rate constant is shown to be dependent on R(-6). The quenching dependence on R strongly suggests that luminescent concentration quenching in a phosphorescent Ir(III) complex:host film is controlled by dipole-dipole deactivating interactions as described by the Förster energy transfer model.
We study energy transfer in efficient polymer electrophosphorescent organic light emitting diodes (PHOLEDs) using poly(9-vinylcarbazole) (PVK) host doped with one or more phosphorescent cyclometalated Ir(III) complexes. Single dopant double heterostructure PHOLEDs exhibited saturated color luminescence due to emissive triplet metal-to-ligand charge-transfer to ground state transitions of the Ir(III) dopants. Blue PHOLEDs, excited by an endothermic process from the host polymer, exhibited an emission maximum at a wavelength of λmax=474 nm, with an external quantum efficiency of ηext=1.3±0.1% and luminous power efficiency of ηp=0.8±0.1 lm/W. The green PHOLED exhibited ηext=5.1±0.1%, with ηext>2% for both red and yellow emission. Resonant energy transfer between green emitting fac-tris (2-phenylpyridyl)Ir(III) and red emitting bis[2-(2′-benzothienyl)-pyridinato-N,C3′](acetylacetonate)Ir(III) was observed to nearly double the efficiency of red emission when both dopants were simultaneously blended in a PVK host. PHOLEDs containing a blend of red, yellow, and blue Ir(III) complex dopants produced white light emission with ηext=2.1±0.1%. Our results suggest that deep lying energy states in the PVK conductive matrix may limit the energy transfer efficiency in phosphor doped polymer OLEDs.
The reactions of iodobenzene with azole compounds, 1,2-disubstituted imidazoles and 2-substituted oxazoles and thiazoles, were examined in the presence of catalytic amounts of Pd(OAc)2 and PPh3 in DMF using alkali metal carbonates as bases. It was found that the coupling products, 5-arylazoles, could be selectively produced in good yields by using Cs2CO3. In the case that their 2-position is unsubstituted, the site could also be arylated. In reactions using bromobenzene in place of iodobenzene, K2CO3 was also as effective as Cs2CO3. The addition of a stoichiometric amount of CuI appeared to specifically promote the reactions of thiazoles as well as those of thiophene derivatives. The reactions of 2-unsubstituted azole compounds with aryl iodides could be mediated by CuI to some extent without using the palladium species to give 2-arylazoles.
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