Title:
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Bis-terdentate cyclometalated iridium complexes and europium-coordinated macrocycles for luminescent devices
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A great deal of interest currently surrounds the development of electrophosphorescent
materials, as they may exhibit efficiencies greater than the theoretical limit of
25% for purely fluorescent materials. The most studied material for such purposes is
jac-Ir(ppY)3, which exhibits efficient green phosphorescence in solution and in
electroluminescent devices. Europium(III) complexes have also received attention for
their narrow bandwidth red emission.
A number of charge-neutral iridium(III) complexes have been prepared as
potential electrophosphorescent materials. Bis-terdentate coordination has been
investigated, in a quest to provide improved stability with respect to jac-Ir(ppY)3
derivatives, an important objective in commercial development. The complexes
described herein are the first examples of iridium bound to NACAN coordinating 1,3-
di(2-pyridyl)benzene derivatives. Methyl substitution at C4 and C6 of the phenyl ring
(i.e. 1,5-di(pyridin-2-yl)-2,4-dimethylbenzene (dpydmbH)) is required to inhibit
competitive cyc1ometalation at these positions. Efficient red emission was observed
from Ir(dpydmb-N,C,N)(dppy-C,N,C) (dppyH2 = 2,6-diphenylpyridine) (Am ax = 585 nm,
PL = 0.21 in degassed CH3CN). Fluorination of the dppy ligand at the 2 and 4 positions
of the phenyl rings results in a simultaneous blue-shift and increase in efficiency
(Amax = 547 nm, PL = 0.41 in degassed CH3CN). These complexes exhibit an unusual
meridional geometry, difficult to achieve for tris-bidentate complexes. The complex
Ir( dpydmb-N,C,N)(ppy-C,N)Cl is exceptionally emissive (Amax = 508 nm, PL = 0.76 in
degassed CH3CN). Ir( dpydmb-N,C,N)(tppic-C,N,0) and Ir( dpydmb-N,C,N)(hbqcC,
N,O) (tppicH2 = 4-p-tolyl-6-phenylpicolinic acid; hbqcH2 = 4-hydroxybenzo[h]quinoline-
2-carboxylic acid) were poorly emissive, attributed to a photo activated
labilisation of the Ir-C bond in solution.
The effect of substitution position of a senslt1s1ng aminobenzophenone
chromophore was investigated in a series of europium(III) macrocyc1ic complexes.
Maximum photoluminescence quantum yield was observed for the para-substituted
isomer, attributed to the distance dependence of the efficiency of energy transfer. An
unexpected rearrangement was observed for the ortho-substituted ligand, resulting in a
quinoline derivative with a rare N-arylated substitution pattern.
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