Bridged diiridium complexes for electrophosphorescent OLEDs : synthesis, X-ray crystal structures, photophysics, and devices.

Bettington, S.; Tavasli, M.; Bryce, M.R.; Batsanov, A.S.; Thompson, A.L.; Al Attar, H.A.; Dias, F.B.; Monkman, A.P.

Abstract

Results are presented which challenge the accepted view that dinuclear transition metal–ligand complexes are unsuitable for organic light-emitting device (OLED) applications due to their low luminescence quantum efficiencies. We establish for the first time that halo- and pseudo-halo-bridged diiridium(III) species are viable electrophosphorescent dopants in OLEDs. New cyclometalated chloro- and isocyanate-bridged diiridium(III) complexes, viz. tetrakis[9,9-dihexyl-2-(pyridin-2-yl)fluorene-C2,N′]-bis(μ-chloro)diiridium(III) [Ir(flpy)2Cl]2 (complex 3) and tetrakis[9,9-dihexyl-2-(pyridin-2-yl)fluorene-C2,N′]-bis(μ-isocyanate)diiridim(III) [Ir(flpy)2NCO]2 (complex 4) were obtained in high yield from the 9,9-dihexyl-2-(pyridin-2-yl)fluorene (flpyH) ligand 1. The X-ray crystal structures are described for 3 and the monomeric complex Ir(flpy)2NCO(DMSO) (5) which was obtained from 4. The solution-state photophysical properties of complexes 3 and 4 are characterised by emission from mixed 3π–π*/3MLCT states at [similar]545–550 nm. Complex 4 displays a solution-state photoluminescence quantum yield which is five times that of the dichloro-bridged analogue 3. This is ascribed to an increase in the ligand-LUMO/metal eg gap which reduces the probability of non-radiative decay processes. Spin-coated organic light emitting devices (OLEDs) made from the host polymer poly(9,9-bis-2-ethylhexylfluorene-2,7-diyl) (PF2/6) end-capped with bis-(4-methylphenyl)phenylamine (PF2/6am4) doped with 12.5 wt% of the complexes 3 and 4 show good stability: turn-on voltages are low (<4 V) with maximum EL intensities of [similar]1300 and 13 000 cd m−2, and peak external quantum efficiencies (EQE) of 0.1 and 0.8%, at ca. 400 and 60 mA cm−2, respectively.

Citation

Bettington, S., Tavasli, M., Bryce, M., Batsanov, A., Thompson, A., Al Attar, H., …Monkman, A. (2006). Bridged diiridium complexes for electrophosphorescent OLEDs : synthesis, X-ray crystal structures, photophysics, and devices. Journal of materials chemistry, 16(11), 1046-1052. https://doi.org/10.1039/b515258e

• Journal Article Type: Article
• Acceptance Date: Dec 12, 2005
• Online Publication Date: Jan 11, 2006
• Publication Date: 2006
• Journal: Journal of Materials Chemistry
• Print ISSN: 0959-9428
• Publisher: Royal Society of Chemistry
• Peer Reviewed: Peer Reviewed
• Volume: 16
• Issue: 11
• Pages: 1046-1052
• DOI: https://doi.org/10.1039/b515258e
• Keywords: CYCLOMETALATED IRIDIUM COMPLEXES; LIGHT-EMITTING DEVICES; ELECTROLUMINESCENT DEVICES; CONJUGATED POLYMERS; OPTICAL-PROPERTIES; LIGANDS; PHOSPHORESCENCE; OLIGOMERS; EMISSION; DIODES