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Ir(III)-Based Phosphors with Bipyrazolate Ancillaries; Rational Design, Photophysics, and Applications in Organic Light-Emitting Diodes

Liao, J.-L.; Chi, Y.; Sie, Z.-T.; Ku, C.-H.; Chang, C.-H.; Fox, M.A.; Low, P.J.; Tseng, M.-R.; Lee, G.-H.

Ir(III)-Based Phosphors with Bipyrazolate Ancillaries; Rational Design, Photophysics, and Applications in Organic Light-Emitting Diodes Thumbnail


Authors

J.-L. Liao

Y. Chi

Z.-T. Sie

C.-H. Ku

C.-H. Chang

P.J. Low

M.-R. Tseng

G.-H. Lee



Abstract

A series of three charge-neutral Ir(III) complexes bearing both neutral chelating ligands 4,4′-di-t-butyl-2,2′-bipyridine (dtbbpy) and monoanionic cyclometalated ligands derived from 2-phenylpyridine (ppyH), together with either two monoanionic ligands (i.e., chloride and monodentate pyrazolate) or a single dianionic chelate derived from 5,5′-di(trifluoromethyl)-3,3′-bipyrazole (bipzH2) or 5,5′-(1-methylethylidene)-bis-(3-trifluoromethyl-1H-pyrazole) (mepzH2), was successfully synthesized. These complexes are derived from a common, structurally characterized, Ir(III) intermediate complex [Ir(dtbbpy) (ppy)Cl2] (1), from treatment of IrCl3·3H2O with equal amount of the diimine (N^N) and precursor of the cyclometalated (C^N) ligands in a form of one-pot reaction. Treatment of 1 with various functional pyrazoles afforded [Ir(dtbbpy) (ppy) (pz)Cl] (2), [Ir(dtbbpy) (ppy) (bipz)] (3), and [Ir(dtbbpy) (ppy) (mepz)] (4), which display intense room-temperature emission with λmax spanning the region between 532 and 593 nm in both fluid and solid states. The Ir(III) complexes, 3 and 4, showcase rare examples of three distinctive chelates (i.e., neutral, anionic, and dianionic) assembled around the central Ir(III) cation. Hybrid density functional theory (DFT; B3LYP) electronic structure calculations on 1–4 reveal the lowest unoccupied molecular orbital to be π*(bpy) in character for all complexes and highest occupied molecular orbital (HOMO) offering d(Ir)−π(phenyl) character for 1, 2, and 4 and π(bipz) character for 3. The different HOMO composition of 3 and 4 is also predicted by calculations using pure DFT (BLYP) and wave function (MP2) methods. On the basis of time-dependent DFT calculations, the emissive processes are dominated by the phenyl group-to-bipyridine, ligand(ppy)-to-ligand(bpy) charge transfer admixed with metal-to-ligand transition for all Ir(III) complexes. Organic light emitting diodes were successfully fabricated. A double emitting layer design was adopted in the device architecture using Ir(III) metal complexes 3 and 4, attaining peak external quantum efficiencies, luminance efficiencies, and power efficiencies of 18.1% (59.0 cd/A and 38.6 lm/W) and 16.6% (53.3 cd/A and 33.5 lm/W), respectively.

Citation

Liao, J., Chi, Y., Sie, Z., Ku, C., Chang, C., Fox, M., …Lee, G. (2015). Ir(III)-Based Phosphors with Bipyrazolate Ancillaries; Rational Design, Photophysics, and Applications in Organic Light-Emitting Diodes. Inorganic Chemistry, 54(22), 10811-10821. https://doi.org/10.1021/acs.inorgchem.5b01835

Journal Article Type Article
Acceptance Date Oct 23, 2015
Publication Date Nov 16, 2015
Deposit Date Nov 26, 2015
Publicly Available Date Mar 28, 2024
Journal Inorganic Chemistry
Print ISSN 0020-1669
Electronic ISSN 1520-510X
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
Volume 54
Issue 22
Pages 10811-10821
DOI https://doi.org/10.1021/acs.inorgchem.5b01835

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Copyright Statement
This document is the Accepted Manuscript version of a Published Work that appeared in final form in Inorganic Chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/acs.inorgchem.5b01835.




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