Iridium(III) Complexes of a Dicyclometalated Phosphite Tripod Ligand: Strategy to Achieve Blue Phosphorescence Without Fluorine Substituents and Fabrication of OLEDs

Planar Chiral Multiple Resonance Thermally Activated Delayed Fluorescence Materials for Efficient Circularly Polarized Electroluminescence

Chiral boron/nitrogen doped multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters are promising for highly efficient and color-pure circularly polarized organic light-emitting diodes (CP-OLEDs). Herein, we report two pairs of MR-TADF materials (Czp-tBuCzB, Czp-POAB) based on planar chiral paracyclophane with photoluminescence quantum yields of up to 98 %. The enantiomers showed symmetric circularly polarized photoluminescence spectra with dissymmetry factors |g_PL | of up to 1.6×10^-3 in doped films. Meanwhile, the sky-blue CP-OLEDs with (R/S)-Czp-tBuCzB showed an external quantum efficiency of 32.1 % with the narrowest full-width at half-maximum of 24 nm among the reported CP-OLEDs, while the devices with (R/S)-Czp-POAB displayed the first nearly pure green CP electroluminescence with |g_EL | factors at the 10^-3 level. These results demonstrate the incorporation of planar chirality into MR-TADF emitter is a reliable strategy for constructing of efficient CP-OLEDs.

Probing the Effects of the Number and Positions of -OCH3 and -CN Substituents on Color Tuning of Ir(III) Complex Derivatives through a Joint Computational and Experimental Study

We performed a joint theoretical and experimental study on sixteen Ir(III) complexes bearing a similar molecular platform of bis(2-phenylbenzothiozolato-N,C^2' ) iridium(III) (acetylacetonate) by grafting -OCH₃ group and/or -CN group on different positions of the C-related arene moiety of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>C</mml:mi> <mml:mspace/> <mml:mover><mml:mspace/> <mml:mo>^</mml:mo></mml:mover> <mml:mspace/> <mml:mi>N</mml:mi></mml:mrow> </mml:math> ligand (C-ring). Our results reveal that the introduction of -CN renders an overall drop in the FMO energy levels while a reverse increase is observed for -OCH₃ . The ortho- and para-sites of the C-ring are more effective substitution positions to modulate the HOMO energy level due to the fact that the electronic density of HOMO mainly locates at them while the meta-site would induce a stronger impact on LUMO since the electronic density of LUMO mainly distributes over the position. Utilizing the synergistic effects of the substituents and the substituted positions, a wide color-tuning range from 479 nm to 637 nm was achieved, which covers nearly the whole window of visible spectrum. In particular, the tri-substituted Ir35mo4cn complex (λ_em max =637 nm) may be a potential candidate for high efficiency red OLEDs materials due to its greatly enhanced absorption processes, relatively higher ³ MLCT (%), lower ΔE_S1-T1 , enlarged separation between ³ MLCT/π-π* and ³ MC d-d states, and good hole and particle-transporting performances. Finally, six representative complexes were synthesized and their spectra were determined, which confirm the reliability of our computational strategy.

Emissive Iridium(III) Complexes with Phosphorous-Containing Ancillary

Ir(III) metal complexes and related emitters bearing all kind of cyclometalated chromophoric chelates and non-chromophoric ancillary are extensively studied during the past three decades. Many of them have been found to display bright room temperature phosphorescence from triplet excited states in both solution and solid states, offering a possible application in contemporary optoelectronic technologies, including organic light emitting diodes, electrochemiluminescence, biological imaging and chemical sensing. Among reported materials, there are Ir(III) complexes with at least one phosphorus (P)-containing ligand and/or ancillary chelate, together with cyclometalates or equivalents that are in control of the actual emission energy. Particularly, possession of P-based donor can lead to divergent structural and photophysical properties compared to the traditional designs. This review aims to provide a literature overview as well as the authors' personal account to the development of relevant Ir(III) based phosphors bearing these P-donors. To the readers' convenience, the contents are subdivided into six sessions, according to whether or not they are charge natural, or with mono- or dianionic electronic character, and in accordance to their divergent bonding modes, i. e. monodentate, bidentate and tripodal coordination. In many cases, the P-based ancillaries offer an easy accessible route to the formation of efficient sky-blue and true-blue emitters due to their π-accepting property, together with enlarged emission energy gap and destabilized upper lying quenching state.

Efficient electroluminescence of bluish green iridium complexes with 2-(3,5-bis(trifluoromethyl)phenyl)pyrimidine and 2-(3,5-bis(trifluoromethyl)phenyl)-5-fluoropyrimidine as the main ligands

Four bluish green iridium complexes with high photoluminescence quantum efficiencies were applied in OLEDs, and they showed a maximum current efficiency of 74.70 cd A⁻¹ and a maximum external quantum efficiency of 35.0% with mild efficiency roll-off.

Density functional theory investigation on iridium(iii) complexes for efficient blue electrophosphorescence

The geometrical structures, electronic structures, optoelectronic properties and phosphorescence efficiencies of blue-emitting phosphors [Ir(fpmi)2(pyim)], [Ir(pyim)2(fpmi)], [Ir(fpmi)2(fptz)], [Ir(fpmi)2(pypz)] and [Ir(tfmppz)2(pyim)]), were investigated by DFT and TDDFT methods.

Synthesis, Properties, and Light-Emitting Electrochemical Cell (LEEC) Device Fabrication of Cationic Ir(III) Complexes Bearing Electron-Withdrawing Groups on the Cyclometallating Ligands

The structure–property relationship study of a series of cationic Ir(III) complexes in the form of [Ir(C^N)₂(dtBubpy)]PF₆ [where dtBubpy = 4,4′-di-tert-butyl-2,2′-bipyridine and C^N = cyclometallating ligand bearing an electron-withdrawing group (EWG) at C₄ of the phenyl substituent, i.e., −CF₃ (1), −OCF₃ (2), −SCF₃ (3), −SO₂CF₃ (4)] has been investigated. The physical and optoelectronic properties of the four complexes were comprehensively characterized, including by X-ray diffraction analysis. All the complexes exhibit quasireversible dtBubpy-based reductions from −1.29 to −1.34 V (vs SCE). The oxidation processes are likewise quasireversible (metal + C^N ligand) and are between 1.54 and 1.72 V (vs SCE). The relative oxidation potentials follow a general trend associated with the Hammett parameter (σ) of the EWGs. Surprisingly, complex 4 bearing the strongest EWG does not adhere to the expected Hammett behavior and was found to exhibit red-shifted absorption and emission maxima. Nevertheless, the concept of introducing EWGs was found to be generally useful in blue-shifting the emission maxima of the complexes (λ_em = 484–545 nm) compared to that of the prototype complex [Ir(ppy)₂(dtBubpy)]PF₆ (where ppy = 2-phenylpyridinato) (λ_em = 591 nm). The complexes were found to be bright emitters in solution at room temperature (Φ_PL = 45–66%) with microsecond excited-state lifetimes (τ_e = 1.14–4.28 μs). The photophysical properties along with density functional theory (DFT) calculations suggest that the emission of these complexes originates from mixed contributions from ligand-centered (LC) transitions and mixed metal-to-ligand and ligand-to-ligand charge transfer (LLCT/MLCT) transitions, depending on the EWG. In complexes 1, 3, and 4 the ³LC character is prominent over the mixed ³CT character, while in complex 2, the mixed ³CT character is much more pronounced, as demonstrated by DFT calculations and the observed positive solvatochromism effect. Due to the quasireversible nature of the oxidation and reduction waves, fabrication of light-emitting electrochemical cells (LEECs) using these complexes as emitters was possible with the LEECs showing moderate efficiencies.

A series of heteroleptic cationic Ir(III) complexes bearing electron-withdrawing groups −CF₃ (1), −OCF₃ (2), −SCF₃ (3), −SO₂CF₃ (4) on the cyclometallating ligands have been synthesized, and their optoelectronic properties have been characterized. Though clear trends were found for the ground-state properties, anomalous behavior was observed for the emission maxima. Thus, this study demonstrates that the common design paradigm for blue-shifting emission through addition of EWGs on the C^N ligands is not always operative.

Synthesis, characterization, photophysics and electrochemical study of luminescent iridium(III) complexes with isocyanoborate ligands

A new series of cyclometalated iridium(III) complexes with isocyanoborate ligands [Ir(R2ppy)2(L)(CNBR'3)] (R = H or F; L = CNC6H4Cl-4 or PPh3; R' = Ph, C6F5 or C6H4Cl-4), [Ir(biqb)(ppy)(CNBR''3)] (R'' = C6F5 or C6H4Cl-4) and {Ir(ppy)2(CN)n[CNB(C6F5)3]2-n}(-) (n = 0 or 1) have been synthesized and characterized. Three of these complexes have also been structurally characterized by X-ray crystallography. The photophysical and electrochemical properties of these complexes have been investigated. The effects of isocyanoborate ligands on the luminescence properties of these iridium(III) complexes are also described.