Unusual dual-emissive heteroleptic iridium complexes incorporating TADF cyclometalating ligands

Benjamin, Helen; Zheng, Yonghao; Kozhevnikov, Valery N.; Siddle, Jamie S.; O’Driscoll, Luke J.; Fox, Mark A.; Batsanov, Andrei S.; Griffiths, Gareth C.; Dias, Fernando B.; Monkman, Andrew P.

doi:10.1039/c9dt04672k

Cited by 22 publications

(16 citation statements)

References 47 publications

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“…The key point here, however, is that the room-temperature emissions of both 3 and 5 are probably strongly contributed by the excited state(s) laying above the T 1 state with an intensity share of about 50%. Such a photophysical behavior of 3 and 5 relates them with materials characterized with thermally activated delayed fluorescence (TADF), where the thermally populated state S 1 significantly enhances the emission rate with temperature increase. , To the best of our knowledge, these are the first examples of Ir(III) complexes exhibiting a photophysical behavior similar to TADF materials without a specifically designed ligand (compare to ref ). In line with this behavior is the slight blue-shift of the emission maxima of 3 and 5 in toluene from T = 77 K to T = 300 K (Figure and Table ), which contrasts the Ir(III) complexes that show only a T 1 → S 0 emission where the T = 300 K spectrum is red-shifted from the T = 77 K spectrum due to the better solvation and stabilization of the emitting state T 1 in liquid media. − In toluene dissolved complexes 3 and 5 at T = 300 K, the effect of the better solvation of the T 1 state, compared to that at T = 77 K, is counteracted by the more efficient thermal population of the discussed higher-lying state(s) that contribute to the emission.…”

Section: Resultsmentioning

confidence: 80%

Non-Stereogenic Dinuclear Ir(III) Complex with a Molecular Rack Design to Afford Efficient Thermally Enhanced Red Emission

et al. 2021

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Cyclometalated complexes containing two or more metal centers were recently shown to offer photophysical properties that are advantageous compared to their mononuclear analogues. Here we report the design, synthesis, and luminescent properties of a dinuclear Ir(III) complex formed by a ditopic N^C^N–N^C^N bridging ligand (L1) with pyrimidine as a linking heterocycle. Two dianionic C^N^C terminal ligands were employed to achieve a charge-neutral and nonstereogenic dinuclear complex 5. This complex shows a highly efficient red emission with a maximum at λem = 642 nm as measured for a toluene solution. The decay time and emission quantum yield of the complex measured for the degassed sample are τ = 1.31 μs and ΦPL = 80%, respectively, corresponding to the radiative rate of k r = 6.11·105 s–1. This rate value is approximately fourfold faster than for the green-emitting mononuclear analogue 3. Cryogenic temperature measurements show that the three substrates of the lowest triplet state T1 of 5 emit with decay times of τ(I) = 120 μs, τ(II) = 7 μs, and τ(III) = 1 μs that are much shorter compared to those of the mononuclear complex 3, which has values of τ(I) = 192 μs, τ(II) = 65.6 μs, and τ(III) = 3.6 μs. These data indicate that the spin–orbit coupling of state T1 with the singlet states is much stronger in the case of complex 5, which results in a much higher T1 → S0 emission rate. Indeed, a computational analysis suggests that in the dinuclear complex 5 the T1 state is spin–orbit coupled with twice the number of singlet states compared to that of mononuclear 3, which is a result of the electronic coupling of two coordination sites. The investigation of the temperature dependence of the emission rates of 3 and 5 shows that the room-temperature emission of both complexes is mainly contributed by a thermally populated excited state lying above the T1 state. To the best of our knowledge, complexes 3 and 5 are the first examples of Ir(III) complexes that show photophysical behavior reminiscent of thermally activated delayed fluorescence (TADF).

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Section: Resultsmentioning

confidence: 80%

Non-Stereogenic Dinuclear Ir(III) Complex with a Molecular Rack Design to Afford Efficient Thermally Enhanced Red Emission

et al. 2021

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“…[ 15 ] Examples include a small number of iridium(III) complexes with both metal‐to‐ligand charge transfer and ligand triplet emission [ 16 ] or phosphorescence and ligand based TADF emission. [ 17 ] In the latter case the TADF character was proposed to arise from the carbazole moieties being covalently linked to the pyridine moiety of the ligand, which was deemed a weak acceptor. The molecules were found to undergo solvatochromism and the dual emission was reported to be due to the interconversion of energy between the triplet charge transfer states ( 3 CT) and triplet metal‐to‐ligand charge transfer states ( 3 MLCT) of the TADF and phosphorescent moieties, respectively.…”

Section: Introductionmentioning

confidence: 99%

Properties of Dual Emissive Dendrimers Based on ThermallyActivated Delayed Fluorescence Dendrons and a Phosphorescent Ir(ppy)₃ Core

Thamarappalli

Ranasinghe

Jang

et al. 2022

Adv Funct Materials

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Dual emission light‐emitting dendrimers composed of phosphorescent fac‐tris[2‐phenylpyridyl]iridium(III) [Ir(ppy)3] cores and thermally activated delayed fluorescence‐based (TADF‐based) dendrons have been prepared. The TADF‐based dendrons are designed to have green or blue emission. The dendrimers show solvatochromism, with the emission switching between phosphorescence and TADF depending on the medium in which the measurement is undertaken. Time‐dependent photoluminescence (PL) spectra measurements show that the TADF dendrons can act as an energy pool for emission from the phosphorescent core. The PL quantum yields (PLQYs) are found to be strongly dependent on the dielectric constant of the solvent, ranging from as high as 76% to as low as 0.3%. Neat films of the dendrimers are found to have relatively balanced hole and electron mobilities of order 10–6 cm2 V–1 s–1, with bilayer organic light‐emitting diodes (OLEDs) containing neat emissive layers having a maximum external quantum efficiency (EQE) of 4.7% for a film having a PLQY of 12%. Finally, the solution processed OLEDs fabricated using 0.4 mol% of the dendrimers blended with 9‐[3‐(9H‐carbazol‐9‐yl)phenyl]‐9H‐carbazole‐3‐carbonitrile result in green emission with maximum EQEs of 9.8% and 15.1% for the dendrimers with green and blue emissive TADF dendrons, respectively.

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“…A class of emitters of noticeable interest is formed by compounds bearing three bidentate three-electron-donor ligands (3b), of two different types, usually two orthometalated 2-aryl-pyridines and other one. These molecules [3b + 3b + 3b′] are generally prepared from [Ir(μ-Cl)(3b) 2 ] 2 dimers . Thus, the selective bromination of these starting materials should allow developing synthetic methodologies of postfunctionalization from the origin, reducing the issues of competitive functionalization and side reactions in subsequent steps.…”

Section: Introductionmentioning

confidence: 99%

Bromination and C–C Cross-Coupling Reactions for the C–H Functionalization of Iridium(III) Emitters

et al. 2021

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The orthometalated phenyl groups of the dimer [Ir(μ-Cl){κ 2 -C,N-(C 6 H 3 Me-py)} 2 ] 2 have been selectively brominated, at para-position with regard to the Ir−C bonds, with Nbromosuccinimide. The bromination leads to [Ir(μ-Cl){κ 2 -C,N-(C 6 H 2 MeBr-py)} 2 ] 2 , which affords the mononuclear derivatives Ir{κ 2 -C,N-(C 6 H 2 MeBr-py)} 2 {κ 2 -O,N-[OC(O)-py]}, Ir{κ 2 -C,N-(C 6 H 2 MeBr-py)} 2 {κ 2 -O,O-(acac)}, and Ir{κ 2 -C,N-(C 6 H 2 MeBr-py)} 2 {κ 2 -C,N-[C 6 H 4 -Mepy]} by replacement of the chloride bridges by a picolinate anion, an acac group, and an orthometalated 2-phenyl-5-methylpyridine ligand, respectively. Complexes Ir{κ 2 -C,N-(C 6 H 2 MeBr-py)} 2 {κ 2 -O,O-(acac)} and Ir{κ 2 -C,N-(C 6 H 2 MeBr-py)} 2 {κ 2 -C,N-[C 6 H 4 -Mepy]} have been subsequently postfunctionalized by means of palladium-catalyzed Suzuki−Miyaura cross-coupling to give Ir{κ 2 -C,N-(C 6 H 2 MeR-py)} 2 {κ 2 -O,O-(acac)} (R = Me, Ph) and Ir{κ 2 -C,N-(C 6 H 2 Me 2 -py)} 2 {κ 2 -C,N-[C 6 H 4 -Mepy]}. These [3b + 3b + 3b′] mononuclear compounds are green-yellow emitters (488−580 nm) upon photoexcitation, in doped poly(methyl methacrylate) (PMMA) film at 5 wt % at room temperature and 2-methyltetrahydrofuran (2-MeTHF) at room temperature and at 77 K. They display lifetimes in the range 1.0−5.0 μs and quantum yields in PMMA films and in 2-MeTHF at room temperature between 0.84 and 0.40.

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Unusual dual-emissive heteroleptic iridium complexes incorporating TADF cyclometalating ligands

Abstract: Five new neutral heteroleptic iridium(iii) complexes IrL2(pic) (2–6) based on the archetypical blue emitter FIrpic have been synthesised.

Cited by 22 publications

References 47 publications

Non-Stereogenic Dinuclear Ir(III) Complex with a Molecular Rack Design to Afford Efficient Thermally Enhanced Red Emission

Non-Stereogenic Dinuclear Ir(III) Complex with a Molecular Rack Design to Afford Efficient Thermally Enhanced Red Emission

Properties of Dual Emissive Dendrimers Based on ThermallyActivated Delayed Fluorescence Dendrons and a Phosphorescent Ir(ppy)₃ Core

Bromination and C–C Cross-Coupling Reactions for the C–H Functionalization of Iridium(III) Emitters

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Unusual dual-emissive heteroleptic iridium complexes incorporating TADF cyclometalating ligands

Abstract: Five new neutral heteroleptic iridium(iii) complexes IrL2(pic) (2–6) based on the archetypical blue emitter FIrpic have been synthesised.

Cited by 22 publications

References 47 publications

Non-Stereogenic Dinuclear Ir(III) Complex with a Molecular Rack Design to Afford Efficient Thermally Enhanced Red Emission

Non-Stereogenic Dinuclear Ir(III) Complex with a Molecular Rack Design to Afford Efficient Thermally Enhanced Red Emission

Properties of Dual Emissive Dendrimers Based on ThermallyActivated Delayed Fluorescence Dendrons and a Phosphorescent Ir(ppy)3 Core

Bromination and C–C Cross-Coupling Reactions for the C–H Functionalization of Iridium(III) Emitters

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Properties of Dual Emissive Dendrimers Based on ThermallyActivated Delayed Fluorescence Dendrons and a Phosphorescent Ir(ppy)₃ Core