Archetypal Iridium(III) Compounds for Optoelectronic and Photonic Applications

Deaton, Joseph C.; Castellano, Felix N.

doi:10.1002/9781119007166.ch1

Cited by 89 publications

(118 citation statements)

References 297 publications

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“…Thus, the TADF decay time drops to the record value of τ (TADF, 300 K)=1.4 μs. Moreover, the Ag I complex represents the first TADF material with a radiative decay time comparable to those of Ir III complexes that have become famous for OLED applications.…”

Section: Design Strategies For Highly Efficient Agi‐based Tadf Compomentioning

confidence: 99%

TADF Material Design: Photophysical Background and Case Studies Focusing on Cu^Iand Ag^IComplexes

et al. 2017

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The development of organic light emitting diodes (OLEDs) and the use of emitting molecules have strongly stimulated scientific research of emitting compounds. In particular, for OLEDs it is required to harvest all singlet and triplet excitons that are generated in the emission layer. This can be achieved using the so-called triplet harvesting mechanism. However, the materials to be applied are based on high-cost rare metals and therefore, it has been proposed already more than one decade ago by our group to use the effect of thermally activated delayed fluorescence (TADF) to harvest all generated excitons in the lowest excited singlet state S . In this situation, the resulting emission is an S →S fluorescence, though a delayed one. Hence, this mechanism represents the singlet harvesting mechanism. Using this effect, high-cost and strong SOC-carrying rare metals are not required. This mechanism can very effectively be realized by use of Cu or Ag complexes and even by purely organic molecules. In this investigation, we focus on photoluminescence properties and on crucial requirements for designing Cu and Ag materials that exhibit short TADF decay times at high emission quantum yields. The decay times should be as short as possible to minimize non-radiative quenching and, in particular, chemical reactions that frequently occur in the excited state. Thus, a short TADF decay time can strongly increase the material's long-term stability. Here, we study crucial parameters and analyze their impact on the TADF decay time. For example, the energy separation ΔE(S -T ) between the lowest excited singlet state S and the triplet state T should be small. Accordingly, we present detailed photophysical properties of two case-study materials designed to exhibit a large ΔE(S -T ) value of 1000 cm (120 meV) and, for comparison, a small one of 370 cm (46 meV). From these studies-extended by investigations of many other Cu TADF compounds-we can conclude that just small ΔE(S -T ) is not a sufficient requirement for short TADF decay times. High allowedness of the transition from the emitting S state to the electronic ground state S , expressed by the radiative rate k (S →S ) or the oscillator strength f(S →S ), is also very important. However, mostly small ΔE(S -T ) is related to small k (S →S ). This relation results from an experimental investigation of a large number of Cu complexes and basic quantum mechanical considerations. As a consequence, a reduction of τ(TADF) to below a few μs might be problematic. However, new materials can be designed for which this disadvantage is not prevailing. A new TADF compound, Ag(dbp)(P -nCB) (with dbp=2,9-di-n-butyl-1,10-phenanthroline and P -nCB=bis-(diphenylphosphine)-nido-carborane) seems to represent such an example. Accordingly, this material shows TADF record properties, such as short TADF decay time at high emission quantum yield. These properties are based (i) on geometry optimizations of the Ag complex for a fast radiative S →S rate and (ii) on restricting the extent of geometry reorganiza...

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Section: Design Strategies For Highly Efficient Agi‐based Tadf Compomentioning

confidence: 99%

TADF Material Design: Photophysical Background and Case Studies Focusing on Cu^Iand Ag^IComplexes

et al. 2017

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“…As recently disclosed, the excited state potential energy surfaces (PES) of these complexes, but also in the case of e. g., [Ru(bpy) 3 ] 2 + , [19] might be more complex than originally believed. [24][25][26] These isomerization reactions might importantly modify the spectral features and efficiencies of PhOLEDs devices, [27] since the stereoisomers (i. e., facial (fac-) and meridional (mer-) stereoisomers) are known to possess different photophysical properties. [19] Besides being relevant for PhOLEDs' degradation, 3 MC states also act as very efficient funnels for the radiationless deactivation to the 1 GS, due to the presence of minimum energy crossing points (MECP) between the 1 GS and 3 MC PES.…”

Section: Mer-ir(ppy) 3 To Fac-ir(ppy) 3 Photoisomerizationmentioning

confidence: 99%

“…Evidence shows that the population of higher-lying excited states, and particularly, triplet metalcentered ( 3 MC) excited states, [10,16] strongly enhances these degradation processes. [24][25][26] These isomerization reactions might importantly modify the spectral features and efficiencies of PhOLEDs devices, [27] since the stereoisomers (i. e., facial (fac-) and meridional (mer-) stereoisomers) are known to possess different photophysical properties. For instance, in cyclometalated Ir(III) complexes, both 1 GS and T 1 exhibit a pseudo-octahedral geometrical disposition while the 3 MC state often displays a pentacoordinate trigonal bipyramid arrangement bearing one broken IrÀ N bond.…”

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confidence: 99%

Mer‐Ir(ppy)₃ to Fac‐Ir(ppy)₃ Photoisomerization

Escudero

2019

ChemPhotoChem

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In this contribution a detailed mechanistic investigation of merto-fac photoisomerization occurring in Ir(ppy) 3 (ppy = 2-phenylpyridine) is presented. Facial/meridional stereoisomerism in trisbidentate Ir(III) complexes strongly determines their photophysical properties and thereby their efficiency and stability within a phosphorescence-based organic light-emitting diode (PhOLED) device. Double-hybrid density functional theory (DFT) calculations are performed herein to identify the photoactive species involved in the photoisomerization reaction and to assess its kinetic and thermodynamic feasibility at room temperature. These investigations highlight the protagonistic role of a non-previously described 3 MC (triplet metal-centred) state bearing one stretched trans Ir-N position. Finally, and in view of the computed evidences, phosphor design strategies to prevent photoisomerization are proposed.Organometallic complexes of Ir(III) and/or Pt(II) are widely used as efficient phosphors for phosphorescent-based organic lightemitting diodes (PhOLEDs). [1,2] To further improve their device operational lifetimes, and especially in the case of blue phosphors, it is crucial to acquire durable and efficient materials that do not suffer intrinsic chemical degradation upon PhOLED operation. [3][4][5][6][7][8] Degradation of PhOLEDs' materials originates from parasitic exciton-polaron and exciton-exciton annihilation processes, [4,7] such as e. g., triplet-triplet annihilation (TTA) and triplet-polaron annihilation (TPA), which also compromise PhOLEDs efficiency at high brightness levels (i. e., roll-off effect). [9] In recent years, numerous computational [10][11][12] and experimental [13][14][15][16] efforts have been made to decipher the underlying degradation mechanisms, and still many open questions remain. In the case of phosphors, ligand dissociation reactions are the most common degradation routes. [7,16] These reactions lead to the formation of products in an irreversible manner that act as nonradiative recombination sites, charge traps and/or luminescence quenchers. Thus, these final products are ultimately responsible for the significant luminance loss in the aged devices. Evidence shows that the population of higher-lying excited states, and particularly, triplet metalcentered ( 3 MC) excited states, [10,16] strongly enhances these degradation processes. 3 MC states are usually highly distorted with respect to the ground state ( 1 GS) and lowest triplet (T 1 ) excited state geometries, [17] the latter typically being of predominant metal-to-ligand charge transfer character, i. e., 3 MLCT. For instance, in cyclometalated Ir(III) complexes, both 1 GS and T 1 exhibit a pseudo-octahedral geometrical disposition while the 3 MC state often displays a pentacoordinate trigonal bipyramid arrangement bearing one broken IrÀ N bond. [17,18] Therefore, ligand dissociation is more likely to occur from a 3 MC state than from either 1 GS or T 1 . As recently disclosed, the excited state potential energy surfaces (PES) of these co...

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“…Transition-metal complexes that exhibit long-lived and highly efficient luminescence remaint he focuso fi ntense study because of their use in av ariety of photochemical, photobiological, biomedical, and optoelectronic applications,i ncluding chemicala nd biological sensing, [1][2][3] cell imaging, [4][5][6][7] photocatalysis in organic synthesis, [8,9] photodynamic therapy, [10,11] and electroluminescent materials for lighting and displays. [12][13][14][15] Complexes of Ir III [16,17] and Pt II [18,19] with cyclometalating heteroaromatic ligands have been the focus of the majority of research efforts in this field during the most recent decades because of the high versatility of their excited states,a lthough complexes of Au III are being increasingly studied. [20,21] In comparison, cyclometalated Pt IV complexes are very scarce and the study of their photophysical properties is still underdeveloped.…”

Section: Introductionmentioning

confidence: 99%

Luminescent Platinum(IV) Complexes Bearing Cyclometalated 1,2,3‐Triazolylidene and Bi‐ or Terdentate 2,6‐Diarylpyridine Ligands

Vivancos

Bautista

González‐Herrero

2019

Chemistry A European J

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The synthesis, structure, and photophysical properties of luminescent PtIV complexes that combine cyclometalated 1,2,3‐triazolylidene and bi‐ or terdentate 2,6‐diarylpyridine ligands are reported. The targeted complexes represent the first examples of PtIV species with a cyclometalated mesoionic aryl‐NHC ligand. They exhibit moderate or weak emissions in fluid solution at 298 K arising from 3LC states, which become very intense in poly(methyl methacrylate) (PMMA) matrices at 298 K. DFT and TD‐DFT calculations confirm that the chromophoric ligand is the cyclometalated 2,6‐diarylpyridine and show that the aryl‐NHC ligand exerts a beneficial effect on the emission efficiencies of these derivatives by increasing the energy of deactivating LMCT excited states with respect to comparable PtIV complexes with cyclometalated 2‐arylpyridine ligands.

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Archetypal Iridium(III) Compounds for Optoelectronic and Photonic Applications

Cited by 89 publications

References 297 publications

TADF Material Design: Photophysical Background and Case Studies Focusing on Cu^Iand Ag^IComplexes

TADF Material Design: Photophysical Background and Case Studies Focusing on Cu^Iand Ag^IComplexes

Mer‐Ir(ppy)₃ to Fac‐Ir(ppy)₃ Photoisomerization

Luminescent Platinum(IV) Complexes Bearing Cyclometalated 1,2,3‐Triazolylidene and Bi‐ or Terdentate 2,6‐Diarylpyridine Ligands

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Archetypal Iridium(III) Compounds for Optoelectronic and Photonic Applications

Cited by 89 publications

References 297 publications

TADF Material Design: Photophysical Background and Case Studies Focusing on CuIand AgIComplexes

TADF Material Design: Photophysical Background and Case Studies Focusing on CuIand AgIComplexes

Mer‐Ir(ppy)3 to Fac‐Ir(ppy)3 Photoisomerization

Luminescent Platinum(IV) Complexes Bearing Cyclometalated 1,2,3‐Triazolylidene and Bi‐ or Terdentate 2,6‐Diarylpyridine Ligands

Contact Info

Product

Resources

About

TADF Material Design: Photophysical Background and Case Studies Focusing on Cu^Iand Ag^IComplexes

TADF Material Design: Photophysical Background and Case Studies Focusing on Cu^Iand Ag^IComplexes

Mer‐Ir(ppy)₃ to Fac‐Ir(ppy)₃ Photoisomerization