A series of bis-cyclometalated iridium complexes were prepared which combine triazole or NHC-based cyclometalating ligands with substituted β-diketiminate (NacNac) ancillary ligands. The HOMO is localized on the NacNac ligand and its energy and associated redox potential are determined by the NacNac substitution pattern. The effect of the cyclometalating ligand, relative to the more common 2-phenylpyridine derivatives, is to destabilize the LUMO and increase the triplet excited-state energy ( E T1 ). These results are supported by DFT calculations, which show HOMOs and LUMOs that are respectively localized on the NacNac and cyclometalating ligands. With this new design, we observe more negative excited-state reduction potentials, E (Ir IV /*Ir III ), with two members of the series standing out as the most potent visible-light iridium photoreductants ever reported. Stern–Volmer quenching experiments with ketone acceptors (benzophenone and acetophenone) show that the increased thermodynamic driving force for photoinduced electron-transfer correlates with faster rates relative to fac -Ir(ppy) 3 and previous generations of NacNac-supported iridium complexes. A small selection of photoredox transformations is shown, demonstrating that these new photoreductants are capable of activating challenging organohalide substrates, albeit with modest conversion.
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Mixed-carbene cyclometalated iridium complexes with saturated blue luminescence
Cyclometalated iridium complexes have emerged as top-performing emitters in organic light-emitting diodes (OLEDs) and other optoelectronic devices. A persistent challenge has been the development of cyclometalated iridium complexes with deep blue luminescence that have the requisite color purity, efficiency, and stability to function in color displays. In this work we report a new class of cyclometalated iridium complexes with saturated blue luminescence. These complexes have the general structure Ir(C^C: NHC ) 2 (C^C: ADC ), where C^C: NHC is an N-heterocyclic carbene (NHC) derived cyclometalating ligand and C^C: ADC is a different type of cyclometalating ligand featuring an acyclic diaminocarbene (ADC). The complexes are prepared by a cascade reaction that involves nucleophilic addition of propylamine to an isocyanide precursor followed by base-assisted cyclometalation of the ADC intermediate. All three emit deep blue light with good quantum efficiencies ( Φ PL = 0.13–0.48) and color profiles very close to the ideal primary blue standards for color displays.
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- Award ID(s):
- 1846831
- NSF-PAR ID:
- 10317918
- Date Published:
- Journal Name:
- Chemical Science
- Volume:
- 10
- Issue:
- 25
- ISSN:
- 2041-6520
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C9SC01386E
