Blue Phosphorescence with High Quantum Efficiency Engaging the Trifluoromethylsulfonyl Group to Iridium Phenylpyridine Complexes

Abstract

Incorporation of an electron-withdrawing −SO2CF3 substituent to cyclometalating C^N-phenylpyridine (ppy) ligand resulted in an expected blue-shifted phosphorescence in the corresponding homoleptic Ir­(ppySCF 3 ) 3 complex, showing the emission of λem = 464 nm at 300 K. One of its heteroleptic derivatives, modified by a pyrazolyl borate LX ligand, Ir­(ppySCF 3 ) 2 (bor), exhibited further blue-shifted phosphorescence of λem = 460 nm at 300 K. Cyclic voltammograms (CVs) and density-functional theory (DFT) calculations supported the efficacy of the electron-withdrawing capability of the SO2CF3 substituent lowering HOMO energy and obtained widened bandgaps and resumed blue emissions for all of the iridium complexes studied. The homoleptic complexes of both substituents, Ir­(ppySCF 3 ) 3 and Ir­(ppySF) 3 , reached the higher quantum yields (Φ PL) of (0.89 and 0.72), respectively. Similarly, emission quantum yields (Φ PL) of the heteroleptic derivatives were reported to be (0.75, 0.83, and 0.87) for Ir­(ppySCF 3 ) 2 (acac), Ir­(ppySCF 3 ) 2 (bor), and Ir­(ppySCF 3 ) 2 (pic), respectively. Emission kinetics support the enhanced quantum efficiency when k r and k nr values are compared between Ir­(ppySCF 3 ) 3 and Ir­(ppySF) 3 , and both values favorably contribute to attaining a higher quantum efficiency for Ir­(ppySCF 3 ) 3 . Among solution-processed multilayered devices having an ITO/PEDOT:PSS/TCTA:Ir dopant (10:1, w/w)/TmPyPB/Liq/Al structure, a heteroleptic dopant, Ir­(ppySCF 3 ) 2 (bor), exhibited better device performance, reporting an external quantum efficiency (EQE) of 1.14%, current efficiency (CE) of 2.31 cd A–1, and power efficiency (PE) of 1.21 lm W–1, together with blue chromaticity of CIEx,y = (0.16, 0.32).

High-Throughput Screening and Automated Data-Driven Analysis of the Triplet Photophysical Properties of Structurally Diverse, Heteroleptic Iridium(III) Complexes

“…Second and third row d 6 transition metals, specifically Ru­(II), Re­(I), Os­(II), and Ir­(III), form photoactive coordination complexes suitable for varied applications including light emitting diodes, oxygen sensing, organic photocatalysis, bioimaging, photodynamic therapy, and solar fuel generation. − Heteroleptic [Ir­(C^N) 2 (N^N)] + complexes (where C^N is a cyclometalating 2-phenylpyridyl ligand and N^N is a 1,2-diimine ancillary ligand, Figure A) are popular scaffolds due to their modular synthesis, enhanced photostability, and long-lived triplet excited state lifetimes arising from strong spin–orbital effects of Ir­(III). − Large ligand-field splitting, caused by the high quantum number of the central Ir d -electrons and the strongly σ-donating carbanions of the cyclometalating ligands, significantly destabilizes metal-centered (MC) antibonding orbitals compared to other 4 d and 5 d metal ion complexes . The substantial increase in these e g *-like orbitals inhibits thermal population of the deactivating 3 MC excited state and allows the large variability in emission color of reported Ir­(III) complexes, spanning the visible spectrum (Figure A).…”

“…28−31 Large ligand-field splitting, caused by the high quantum number of the central Ir delectrons and the strongly σ-donating carbanions of the cyclometalating ligands, significantly destabilizes metal-centered (MC) antibonding orbitals compared to other 4d and 5d metal ion complexes. 32 The substantial increase in these e g *like orbitals inhibits thermal population of the deactivating 3 MC excited state and allows the large variability in emission color of reported Ir(III) complexes, spanning the visible spectrum (Figure 1A).…”

Bright Single-Layer Perovskite Host–Ionic Guest Light-Emitting Electrochemical Cells

“…Cyclometallated Ir(III) complexes have been and continue to be of great interest as luminophoric materials for organic photoredox transformations, 41,42 solar energy conversion, 43,44 and organic light emitting devices. 36,45,46 Whereas Zhang et al previously utilized a conventional charge neutral Ir complex as a guest in a perovskite host, 21 we employed an ionic complex to promote phase compatibility with the perovskite host and additional ionic migration functionality. Furthermore, the guest complex should strongly absorb where the perovskite emits and possess a smaller bandgap to promote efficient energy transfer.…”

Insertion of Unsaturated C–C Bonds into the O–H Bond of an Iridium(III)-Hydroxo Complex: Formation of Phosphorescent Emitters with an Asymmetrical β-Diketonate Ligand

“…Among them, octahedral derivatives bearing two different types of 3e-donor bidentate ligands ([3b+3b+3b′]) have received special attention. Commonly, these compounds contain two ortho -metalated phenyl-heterocycles (3b) and an acetylacetonate type ligand (3b′) . The energy of the excited states of these emitters depends upon both the β-diketonate and the heterocycle.…”

“…The synthesis of iridium­(III) emitters generally involves ligand displacement and addition reactions, whereas the generation of structures by means of organometallic transformations on the metal coordination sphere or selective postfunctionalization of a coordinated ligand via catalysis , has been rarely used. In agreement with the general protocol, the [3b+3b+3b′] compounds are usually prepared by reaction of the corresponding dimers [Ir­(μ-Cl)­(3b) 2 ] 2 with a β-diketonate salt . Because symmetrical β-diketones with alkyl or aryl substituents are more common than asymmetrical ones, the symmetrical structures are frequent, whereas the complexes bearing asymmetrical β-diketonate ligands are rare, in particular when one of the substituents is a π-donor group with significant ability to contribute to the aromatic metal-diketonate system …”