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Author

Peter I. Djurovich

Bio: Peter I. Djurovich is an academic researcher from University of Southern California. The author has contributed to research in topics: Phosphorescence & OLED. The author has an hindex of 61, co-authored 169 publications receiving 18806 citations. Previous affiliations of Peter I. Djurovich include California Institute of Technology.
Topics: Phosphorescence, OLED, Excited state, Ligand, Carbene


Papers
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Journal ArticleDOI
TL;DR: The synthesis and photophysical study of a family of cyclometalated iridium(III) complexes are reported, and three of the C(**)N2Ir(acac) complexes were used as dopants for organic light emitting diodes (OLEDs) and show some of the highest efficiencies reported for organic Light Emitting Diodes.
Abstract: The synthesis and photophysical study of a family of cyclometalated iridium(III) complexes are reported. The iridium complexes have two cyclometalated (C∧N) ligands and a single monoanionic, bidentate ancillary ligand (LX), i.e., C∧N2Ir(LX). The C∧N ligands can be any of a wide variety of organometallic ligands. The LX ligands used for this study were all β-diketonates, with the major emphasis placed on acetylacetonate (acac) complexes. The majority of the C∧N2Ir(acac) complexes phosphoresce with high quantum efficiencies (solution quantum yields, 0.1−0.6), and microsecond lifetimes (e.g., 1−14 μs). The strongly allowed phosphorescence in these complexes is the result of significant spin−orbit coupling of the Ir center. The lowest energy (emissive) excited state in these C∧N2Ir(acac) complexes is a mixture of 3MLCT and 3(π−π*) states. By choosing the appropriate C∧N ligand, C∧N2Ir(acac) complexes can be prepared which emit in any color from green to red. Simple, systematic changes in the C∧N ligands, whic...

2,655 citations

Journal ArticleDOI
TL;DR: The synthesis, electrochemistry, and photophysics of a series of square planar Pt(II) complexes are reported, with well-resolved vibronic fine structure observed in all of the emission spectra.
Abstract: The synthesis, electrochemistry, and photophysics of a series of square planar Pt(II) complexes are reported. The complexes have the general structure C∧NPt(O∧O),where C∧N is a monoanionic cyclometalating ligand (e.g., 2-phenylpyridyl, 2-(2‘-thienyl)pyridyl, 2-(4,6-difluorophenyl)pyridyl, etc.) and O∧O is a β-diketonato ligand. Reaction of K2PtCl4 with a HC∧N ligand precursor forms the chloride-bridged dimer, C∧NPt(μ-Cl)2PtC∧N, which is cleaved with β-diketones such as acetyl acetone (acacH) and dipivaloylmethane (dpmH) to give the corresponding monomeric C∧NPt(O∧O) complex. The thpyPt(dpm) (thpy = 2-(2‘-thienyl)pyridyl) complex has been characterized using X-ray crystallography. The bond lengths and angles for this complex are similar to those of related cyclometalated Pt complexes. There are two independent molecular dimers in the asymmetric unit, with intermolecular spacings of 3.45 and 3.56 A, consistent with moderate π−π interactions and no evident Pt−Pt interactions. Most of the C∧NPt(O∧O) complexes...

1,354 citations

Journal ArticleDOI
TL;DR: The synthesis, structures, electrochemistry, and photophysics of a series of facial (fac) and meridional (mer) tris-cyclometalated Ir(III) complexes are reported, and the HOMO levels are a mixture of Ir and ligand orbitals, while the LUMO is predominantly ligand-based.
Abstract: The synthesis, structures, electrochemistry, and photophysics of a series of facial (fac) and meridional (mer) tris-cyclometalated Ir(III) complexes are reported. The complexes have the general formula Ir(C'N)(3) [where C'N is a monoanionic cyclometalating ligand; 2-phenylpyridyl (ppy), 2-(p-tolyl)pyridyl (tpy), 2-(4,6-difluorophenyl)pyridyl (46dfppy), 1-phenylpyrazolyl (ppz), 1-(4,6-difluorophenyl)pyrazolyl (46dfppz), or 1-(4-trifluoromethylphenyl)pyrazolyl (tfmppz)]. Reaction of the dichloro-bridged dimers [(C'N(2)Ir(mu-Cl)(2)Ir(C'N)(2)] with 2 equiv of HC( wedge )N at 140-150 degrees C forms the corresponding meridional isomer, while higher reaction temperatures give predominantly the facial isomer. Both facial and meridional isomers can be obtained in good yield (>70%). The meridional isomer of Ir(tpy)(3) and facial and meridional isomers of Ir(ppz)(3) and Ir(tfmppz)(3) have been structurally characterized using X-ray crystallography. The facial isomers have near identical bond lengths (av Ir-C = 2.018 A, av Ir-N = 2.123 A) and angles. The three meridional isomers have the expected bond length alternations for the differing trans influences of phenyl and pyridyl/pyrazolyl ligands. Bonds that are trans to phenyl groups are longer (Ir-C av = 2.071 A, Ir-N av = 2.031 A) than when they are trans to heterocyclic groups. The Ir-C and Ir-N bonds with trans N and C, respectively, have bond lengths very similar to those observed for the corresponding facial isomers. DFT calculations of both the singlet (ground) and the triplet states of the compounds suggest that the HOMO levels are a mixture of Ir and ligand orbitals, while the LUMO is predominantly ligand-based. All of the complexes show reversible oxidation between 0.3 and 0.8 V, versus Fc/Fc(+). The meridional isomers are easier to oxidize by ca. 50-100 mV. The phenylpyridyl-based complexes have reduction potentials between -2.5 and -2.8 V, whereas the phenylpyrazolyl-based complexes exhibit no reduction up to the solvent limit of -3.0 V. All of the compounds have intense absorption bands in the UV region assigned into (1)(pi --> pi) transitions and weaker MLCT (metal-to-ligand charge transfer) transitions that extend to the visible region. The MLCT transitions of the pyrazolyl-based complexes are hypsochromically shifted relative to those of the pyridyl-based compounds. The phenylpyridyl-based Ir(III) tris-cyclometalates exhibit intense emission both at room temperature and at 77 K, whereas the phenylpyrazolyl-based derivatives emit strongly only at 77 K. The emission energies and lifetimes of the phenylpyridyl-based complexes (450-550 nm, 2-6 micros) and phenylpyrazolyl-based compounds (390-440 nm, 14-33 micros) are characteristic for a mixed ligand-centered/MLCT excited state. The meridional isomers for both pyridyl and pyrazolyl-based cyclometalates show markedly different spectroscopic properties than do the facial forms. Isolated samples of mer-Ir(C( wedge )N)(3) complexes can be thermally and photochemically converted to facial forms, indicating that the meridional isomers are kinetically favored products. The lower thermodynamic stabilities of the meridional isomers are likely related to structural features of these complexes; that is, the meridional configuration places strongly trans influencing phenyl groups opposite each other, whereas all three phenyl groups are opposite pyridyl or pyrazolyl groups in the facial complexes. The strong trans influence of the phenyl groups in the meridional isomers leads to the observation that they are easier to oxidize, exhibit broad, red-shifted emission, and have lower quantum efficiencies than their facial counterparts.

1,161 citations

Journal ArticleDOI
TL;DR: In this paper, a relationship between the energy of the highest occupied molecular orbital (HOMO) and the oxidation potential of molecular organic semiconductors is presented, based on an analysis of image charge forces on spherical molecules positioned near a conductive plane formed by the electrode in an electrochemical cell.

705 citations

Journal ArticleDOI
TL;DR: Electrochemical analysis of the (tpy)2 Ir(LL') complexes shows that the reduction potentials are largely unaffected by variation in the ancillary ligand, whereas the oxidation potentials vary over a much wider range (as much as 400 mV between two different LL' ligands).
Abstract: The synthesis and photophysical characterization of a series of (N,C2‘-(2-para-tolylpyridyl))2Ir(LL‘) [(tpy)2Ir(LL‘)] (LL‘ = 2,4-pentanedionato (acac), bis(pyrazolyl)borate ligands and their analogues, diphosphine chelates and tert-butylisocyanide (CN-t-Bu)) are reported. A smaller series of [(dfppy)2Ir(LL‘)] (dfppy = N,C2‘-2-(4‘,6‘-difluorophenyl)pyridyl) complexes were also examined along with two previously reported compounds, (ppy)2Ir(CN)2- and (ppy)2Ir(NCS)2- (ppy = N,C2‘-2-phenylpyridyl). The (tpy)2Ir(PPh2CH2)2BPh2 and [(tpy)2Ir(CN-t-Bu)2](CF3SO3) complexes have been structurally characterized by X-ray crystallography. The Ir−Caryl bond lengths in (tpy)2Ir(CN-t-Bu)2+ (2.047(5) and 2.072(5) A) and (tpy)2Ir(PPh2CH2)2BPh2 (2.047(9) and 2.057(9) A) are longer than their counterparts in (tpy)2Ir(acac) (1.982(6) and 1.985(7) A). Density functional theory calculations carried out on (ppy)2Ir(CN-Me)2+ show that the highest occupied molecular orbital (HOMO) consists of a mixture of phenyl-π and Ir-d orbitals...

647 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, the performance of an organic light-emitting device employing the green electrophosphorescent material, fac tris(2-phenylpyridine) iridium [Ir(ppy)3] doped into a 4,4′-N,N′-dicarbazole-biphenyl host was described.
Abstract: We describe the performance of an organic light-emitting device employing the green electrophosphorescent material, fac tris(2-phenylpyridine) iridium [Ir(ppy)3] doped into a 4,4′-N,N′-dicarbazole-biphenyl host. These devices exhibit peak external quantum and power efficiencies of 8.0% (28 cd/A) and 31 lm/W, respectively. At 100 cd/m2, the external quantum and power efficiencies are 7.5% (26 cd/A) and 19 lm/W at an operating voltage of 4.3 V. This performance can be explained by efficient transfer of both singlet and triplet excited states in the host to Ir(ppy)3, leading to a high internal efficiency. In addition, the short phosphorescent decay time of Ir(ppy)3 (<1 μs) reduces saturation of the phosphor at high drive currents, yielding a peak luminance of 100 000 cd/m2.

3,594 citations

Journal ArticleDOI
TL;DR: In this paper, the authors demonstrate very high efficiency electrophosphorescence in organic light-emitting devices employing a phosphorescent molecule doped into a wide energy gap host, achieving a maximum external quantum efficiency of 19.0±1.0 and luminous power efficiency of 60±5 lm/W.
Abstract: We demonstrate very high efficiency electrophosphorescence in organic light-emitting devices employing a phosphorescent molecule doped into a wide energy gap host. Using bis(2-phenylpyridine)iridium(III) acetylacetonate [(ppy)2Ir(acac)] doped into 3-phenyl-4(1′-naphthyl)-5-phenyl-1,2,4-triazole, a maximum external quantum efficiency of (19.0±1.0)% and luminous power efficiency of (60±5) lm/W are achieved. The calculated internal quantum efficiency of (87±7)% is supported by the observed absence of thermally activated nonradiative loss in the photoluminescent efficiency of (ppy)2Ir(acac). Thus, very high external quantum efficiencies are due to the nearly 100% internal phosphorescence efficiency of (ppy)2Ir(acac) coupled with balanced hole and electron injection, and triplet exciton confinement within the light-emitting layer.

3,302 citations

Journal ArticleDOI
14 May 2009-Nature
TL;DR: An improved OLED structure which reaches fluorescent tube efficiency and focuses on reducing energetic and ohmic losses that occur during electron–photon conversion, which could make white-light OLEDs, with their soft area light and high colour-rendering qualities, the light sources of choice for the future.
Abstract: The development of white organic light-emitting diodes (OLEDs) holds great promise for the production of highly efficient large-area light sources. High internal quantum efficiencies for the conversion of electrical energy to light have been realized. Nevertheless, the overall device power efficiencies are still considerably below the 60-70 lumens per watt of fluorescent tubes, which is the current benchmark for novel light sources. Although some reports about highly power-efficient white OLEDs exist, details about structure and the measurement conditions of these structures have not been fully disclosed: the highest power efficiency reported in the scientific literature is 44 lm W(-1) (ref. 7). Here we report an improved OLED structure which reaches fluorescent tube efficiency. By combining a carefully chosen emitter layer with high-refractive-index substrates, and using a periodic outcoupling structure, we achieve a device power efficiency of 90 lm W(-1) at 1,000 candelas per square metre. This efficiency has the potential to be raised to 124 lm W(-1) if the light outcoupling can be further improved. Besides approaching internal quantum efficiency values of one, we have also focused on reducing energetic and ohmic losses that occur during electron-photon conversion. We anticipate that our results will be a starting point for further research, leading to white OLEDs having efficiencies beyond 100 lm W(-1). This could make white-light OLEDs, with their soft area light and high colour-rendering qualities, the light sources of choice for the future.

3,095 citations

Journal ArticleDOI
TL;DR: The synthesis and photophysical study of a family of cyclometalated iridium(III) complexes are reported, and three of the C(**)N2Ir(acac) complexes were used as dopants for organic light emitting diodes (OLEDs) and show some of the highest efficiencies reported for organic Light Emitting Diodes.
Abstract: The synthesis and photophysical study of a family of cyclometalated iridium(III) complexes are reported. The iridium complexes have two cyclometalated (C∧N) ligands and a single monoanionic, bidentate ancillary ligand (LX), i.e., C∧N2Ir(LX). The C∧N ligands can be any of a wide variety of organometallic ligands. The LX ligands used for this study were all β-diketonates, with the major emphasis placed on acetylacetonate (acac) complexes. The majority of the C∧N2Ir(acac) complexes phosphoresce with high quantum efficiencies (solution quantum yields, 0.1−0.6), and microsecond lifetimes (e.g., 1−14 μs). The strongly allowed phosphorescence in these complexes is the result of significant spin−orbit coupling of the Ir center. The lowest energy (emissive) excited state in these C∧N2Ir(acac) complexes is a mixture of 3MLCT and 3(π−π*) states. By choosing the appropriate C∧N ligand, C∧N2Ir(acac) complexes can be prepared which emit in any color from green to red. Simple, systematic changes in the C∧N ligands, whic...

2,655 citations

Journal ArticleDOI
TL;DR: The broad tunability and fabrication methods of these materials, the current understanding of the operation of state-of-the-art solar cells and the properties that have delivered light-emitting diodes and lasers are described.
Abstract: Metal-halide perovskites are crystalline materials originally developed out of scientific curiosity. Unexpectedly, solar cells incorporating these perovskites are rapidly emerging as serious contenders to rival the leading photovoltaic technologies. Power conversion efficiencies have jumped from 3% to over 20% in just four years of academic research. Here, we review the rapid progress in perovskite solar cells, as well as their promising use in light-emitting devices. In particular, we describe the broad tunability and fabrication methods of these materials, the current understanding of the operation of state-of-the-art solar cells and we highlight the properties that have delivered light-emitting diodes and lasers. We discuss key thermal and operational stability challenges facing perovskites, and give an outlook of future research avenues that might bring perovskite technology to commercialization.

2,513 citations