Phenanthro[9,10-<i>d</i>]triazole and imidazole derivatives: high triplet energy host materials for blue phosphorescent organic light emitting devices

Idris, Muazzam; Coburn, Caleb; Fleetham, Tyler; Milam-Guerrero, JoAnna; Djurovich, Peter I.; Forrest, Stephen R.; Thompson, Mark E.

doi:10.1039/c9mh00195f

Cited by 41 publications

(39 citation statements)

References 40 publications

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“…This effect of film composition on phosphorescence has been observed previously by others for CBP and its twisted analogue 4,4’‐bis(9‐carbazolyl)‐2,2’‐dimethylbiphenyl CDBP , [27, 54, 73] as well as several other materials [74, 75] . However, despite the logical implications for triplet energies and how these determine host/guest compatibility, it is not commonplace to report neat film phosphorescence of new OLED host materials.…”

Section: Resultssupporting

confidence: 58%

“…Instead, low temperature solution measurements currently dominate the literature in reports of this kind [69, 76–87] . A recent study by Forrest and Thompson [73] has demonstrated that such solution measurements do not give appropriate triplet energies for the design of OLEDs, while the results here show that phosphorescence in dilute polymer films is also not suitable in this regard. We therefore suggest that neat film phosphorescence measurements should become the accepted standard for reporting E T of novel OLED host materials.…”

Section: Resultsmentioning

confidence: 74%

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Conformational Dependence of Triplet Energies in Rotationally Hindered N‐ and S‐Heterocyclic Dimers: New Design and Measurement Rules for High Triplet Energy OLED Host Materials

Wright

Danos

Montanaro

et al. 2021

Chemistry A European J

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A series of four heterocyclic dimers has been synthesized, with twisted geometries imposed across the central linking bond by ortho‐alkoxy chains. These include two isomeric bicarbazoles, a bis(dibenzothiophene‐S,S‐dioxide) and a bis(thioxanthene‐S,S‐dioxide). Spectroscopic and electrochemical methods, supported by density functional theory, have given detailed insights into how para‐ vs. meta‐ vs. broken conjugation, and electron‐rich vs. electron‐poor heterocycles impact the HOMO–LUMO gap and singlet and triplet energies. Crucially for applications as OLED hosts, the triplet energy (ET) of these molecules was found to vary significantly between dilute polymer films and neat films, related to conformational demands of the molecules in the solid state. One of the bicarbazole species shows a variation in ET of 0.24 eV in the different media—sufficiently large to “make‐or‐break” an OLED device—with similar discrepancies found between neat films and frozen solution measurements of other previously reported OLED hosts. From consolidated optical and optoelectronic investigations of different host/dopant combinations, we identify that only the lower ET values measured in neat films give a reliable indicator of host/guest compatibility. This work also provides new molecular design rules for obtaining very high ET materials and controlling their HOMO and LUMO energies.

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Section: Resultssupporting

confidence: 58%

Section: Resultsmentioning

confidence: 74%

Conformational Dependence of Triplet Energies in Rotationally Hindered N‐ and S‐Heterocyclic Dimers: New Design and Measurement Rules for High Triplet Energy OLED Host Materials

Wright

Danos

Montanaro

et al. 2021

Chemistry A European J

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“…[7] The OLED performance parameters are given in Table 4 and plots of device efficiencies versus luminance are given in the Supporting Information. In these devices, fac-Ir(tpz) 3 was used as a blue dopant in an emissive layer comprised of mCBP mCBP/8% Firpic [7] 3. The FIrpic EL spectrum in mCBP consists of two roughly equal intensity peaks.…”

Section: Electroluminescence Propertiesmentioning

confidence: 99%

“…[2] Cyclometalated iridium(III) complexes have emerged as one of the most promising triplet emitters because of their versatile color tunability, chemical stability, good thermal properties, and high photoluminescent quantum yields (Φ PL ). [3][4][5][6][7] These phosphors often involve an octahedral Ir 3+ ion with bidentate ligands, C^N:, comprised of a covalently bonded aryl moiety and a datively bonded nitrogen group, such as pyridyl, to give a tris-cyclometalated complex, Ir(C^N:) 3 . While efficient OLEDs using red and green Ir-based phosphorescent emitters are commercially viable, [8][9][10] the stability of OLEDs using blue-emitting transition metal containing complexes are presently insufficient for practical applications.…”

mentioning

confidence: 99%

Blue Emissive fac/mer‐Iridium (III) NHC Carbene Complexes and their Application in OLEDs

Idris

Kapper

Tadle

et al. 2021

Advanced Optical Materials

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transition metal complexes as phosphorescent emitters, making it possible to harvest both singlet and triplet excitons leading to 100% electroluminescence quantum efficiency. [2] Cyclometalated iridium(III) complexes have emerged as one of the most promising triplet emitters because of their versatile color tunability, chemical stability, good thermal properties, and high photoluminescent quantum yields (Φ PL ). [3][4][5][6][7] These phosphors often involve an octahedral Ir 3+ ion with bidentate ligands, C^N:, comprised of a covalently bonded aryl moiety and a datively bonded nitrogen group, such as pyridyl, to give a tris-cyclometalated complex, Ir(C^N:) 3 . While efficient OLEDs using red and green Ir-based phosphorescent emitters are commercially viable, [8][9][10] the stability of OLEDs using blue-emitting transition metal containing complexes are presently insufficient for practical applications. [11] Recently cyclometalated N-heterocyclic carbene (NHC)-Ir based chromophores, Ir(C^C:) 3 , have attracted attention due to their promising properties as blue emitters. [12][13][14][15][16][17][18][19] These C^C: based emitters have an aryl group as do C^N: ligands, but utilize a carbene in place of the nitrogen basic moiety. Our group reported one of the first blue-emitting Ir-carbene complexes for OLEDs, using N-phenyl, N-methyl-imidazol-2-yl (pmi) and N-phenyl, N-methyl-benzimidazol-2-yl (pmb) ligands. [16] Since then, several homoleptic [20][21][22][23] and heteroleptic [18] derivatives of these complexes have also been reported. These Ir(C^C:) 3 complexes have advantages over blue emissive Ir(C^N:) 3 complexes as they do not suffer from deactivation of the excited state via thermal population of triplet metal-centered ( 3 MC) states, which can severely diminish their Φ PL . Replacing the nitrogen basic moiety in the C^N: ligand with a strong field carbene ligand, largely mitigates this problem by destabilizing the 3 MC states, which makes them thermally inaccessible. Interestingly, it was found that even when the 3 MC states are thermally populated, the carbene iridium complexes were able to undergo reversible population of the radiative state leaving the Ir-carbene bond intact. [24] Since the Ir-N bond dissociation in the excited state has been shown to be problematic in Ir(C^N:) 3 complexes, [4] computational results have suggested that replacement with the stronger IrC carbene bond will result in a more robust emitter. [24,25] Further work on Ir(C^C:) 3 complexes led to the use of the electrophilic N-phenyl, N-methyl-pyridylimidazol-2-yl ligand The photophysical and electrochemical properties of N-heterocyclic carbene complexes of Iridium (III) (Ir(C^C:) 3 , where C^C: = N-phenyl,N-methylpyrazinoimidazol-2-yl (pmpz), N,N-di-p-tolyl-pyrazinoimidazol-2-yl (tpz)) are reported. Facial and meridional isomers of Ir(pmpz) 3 are prepared, but only the facial isomer can be isolated for Ir(tpz) 3 . The fac-Ir(pmpz) 3 and fac-Ir(tpz) 3 complexes have emission maxima at 465 nm in polystyrene, whereas the emission max...

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“…Moreover, the three-component cyclocondensation reaction of tris-aldehyde 3 with 9,10-phenanthrenequinone 25 and ammonium acetate afforded the corresponding tris(1H-phenanthro[9,10-d]imidazole) 26 as a new building block for blue light-emitting materials (Scheme 9). 74 Compound 24 was conrmed by the absence of characteristic absorption bands or signals for CHO, NH 2, or SH in its IR or 1 H NMR spectra. The structure of the tris(imidazole) 26 was dened on the basis of spectral data.…”

Section: Resultsmentioning

confidence: 99%

Synthesis of novel star-shaped molecules based on a 1,3,5-triazine core linked to different heterocyclic systems as novel hybrid molecules

et al. 2020

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Phenanthro[9,10-d]triazole and imidazole derivatives: high triplet energy host materials for blue phosphorescent organic light emitting devices

Abstract: A class of wide bandgap host materials is introduced as an alternative to carbazole-based hosts to enhance the efficiency and transport properties of organic light emitting diodes (OLEDs).

Cited by 41 publications

References 40 publications

Conformational Dependence of Triplet Energies in Rotationally Hindered N‐ and S‐Heterocyclic Dimers: New Design and Measurement Rules for High Triplet Energy OLED Host Materials

Conformational Dependence of Triplet Energies in Rotationally Hindered N‐ and S‐Heterocyclic Dimers: New Design and Measurement Rules for High Triplet Energy OLED Host Materials

Blue Emissive fac/mer‐Iridium (III) NHC Carbene Complexes and their Application in OLEDs

Synthesis of novel star-shaped molecules based on a 1,3,5-triazine core linked to different heterocyclic systems as novel hybrid molecules

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