Bis-terdentate cyclometalated iridium complexes and europium-coordinated macrocycles for luminescent devices

• Main Author: Wilkinson, Andrew John
• Published: Durham University 2004
• Subjects: 621.3273
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.445821

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, <l>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, <l>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, <l>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.