Phosphorescent PtAu2 Complexes with Differently Positioned

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Phosphorescent PtAu2 Complexes with Different Positioned CarbazoleAcetylide Ligands for Solution-Processed OLEDs with EQE over 20% Liang-Jin Xu, Xian-Chong Zeng, Jin-Yun Wang, Li-Yi Zhang, Yun Chi, and Zhong-Ning Chen ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b06707 • Publication Date (Web): 19 Jul 2016 Downloaded from http://pubs.acs.org on July 21, 2016

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ACS Applied Materials & Interfaces

Phosphorescent PtAu2 Complexes with Different Positioned Carbazole-Acetylide Ligands for Solution-Processed OLEDs with EQE over 20% Liang-Jin Xu,† Xian-Chong Zeng,† Jin-Yun Wang,† Li-Yi Zhang,† Yun Chi,‡,* and Zhong-Ning Chen†,* †

State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of

Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China. ‡

Department of Chemistry and Low Carbon Energy Research Center, National Tsing Hua

University, Hsinchu 30013, Taiwan.

ACS Paragon Plus Environment

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ABSTRACT: The utilization of phosphorescent metal cluster complexes as new types of emitting materials in organic light-emitting diodes is becoming an alternative and viable approach for achieving high-efficiency electroluminescence. We report herein the design of cationic PtAu2 cluster complexes with different positioned 9-phenylcarbazole-acetylides to serve as phosphorescent emitters in OLEDs. The rigid structures of PtAu2 complexes cause intense phosphorescence with quantum yield over 85%, which originates from 3[π (phenylcarbazoleacetylide) → π* (dpmp)] 3LLCT and 3[π (phenylcarbazole-acetylide) → p/s (PtAu2)] 3LMCT triplet excited states. Doping 8 wt.% PtAu2 to blended host materials of TCTA and OXD-7 (2 : 1 weight ratio) as light-emitting layers, solution-processed OLEDs give current efficiency (CE) of 78.2 cd A-1 and external quantum efficiency (EQE) of 21.5% at a practical luminance of 1029 cd m-2 with a slow efficiency roll-off upon increase of luminance. This represents the best device performance and the highest efficiency recorded at practical luminance for solution-processed OLEDs.

KEYWORDS:

Organic

light-emitting

diode,

phosphorescence,

solution

process,

electroluminescence, platinum, gold


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INTRODUCTION Phosphorescent complexes of late transition-metal elements such as iridium(III) and platinum(II) have been flourishingly investigated because of their prosperous applications as emissive materials in organic light-emitting diodes (OLEDs).1-11 Since cyclometallated iridium(III) and platinum(II) complexes are charge neutral species in most cases, high-quality devices can be fabricated through thermal evaporation under high vacuum condition. A number of mononuclear cyclometallated platinum(II) complexes have been designed to achieve high-efficiency OLEDs.12-25 Nevertheless, the synthesis of multidentate chelating ligands and cyclometalated complexes involve frequently multi-step synthetic procedures under harsh reaction conditions with relatively low yields. On the other hand, although polynuclear metal cluster complexes exhibit more complicated molecular structures, they are usually accessible in one-step reactions under mild conditions to give high yields. Intermetallic interactions in metal-organic cluster complexes with the energy comparable to that of hydrogen bonds (25−40 kJ mol-1) give rise to additional thermal and photochemical stability. Moreover, the more heavy involvement of metal orbitals to the excited states in polynuclear cluster structures facilitate intersystem crossing from singlet to triplet excited states. Compared with numerous studies on electroluminescent devices of mononuclear metal complexes, systematic explorations on polynuclear cluster complexes for the fabrication of high-efficiency OLEDs remain to be conducted. Although a few oligonuclear complexes such as Cu4,26 Au4,27 Au4Ag2,28 and Ag6Cu29 cluster species have been recently attempt to serve as phosphorescent dopants to achieve efficient OLEDs through solution process, relevant investigations are still in its infancy. Aiming at exploring new types of phosphorescent metal complexes for high-efficiency electroluminescence, we focus on design of rigid d8/d10-d10 heterometallic cluster complexes


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supported

by

bridging

polyphosphine

ligands.28-31

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Making

use

of

bis(2-

diphenylphosphinomethyl)phenylphosphine (dpmp) as a supporting ligand, we are able to prepare highly phosphorescent PtM2 (M = CuI, AgI, AuI) acetylide complexes.30.31 Mild preparative condition, high luminescent quantum yields, good resistance to thermal, chemical and irradiation induced degradation, favorable solubility in organic solvents, and tunable emission by changing d10 metal centers and modifying the ligands allow this class of complexes to act as perfect light-emitting materials for the fabrication of OLEDs through solution process. We describe herein the use of cationic PtAu2 complexes (Scheme 1) with different positioned phenylcarbazole-acetylide ligands as phosphorescent emitters to fabricate high-efficiency OLEDs, which achieved the peak current efficiency (CE) of 78.2 cd A-1 and external quantum efficiency (EQE) of 21.5% at a practical luminance of 1029 cd m-2. This represents the best device performance ever reported for phosphorescent polynuclear cluster complexes and the highest efficiencies recorded at practical luminance for solution-processed OLEDs. R Ph2P Au Ph2P

PPh

PPh2

Pt

Au

P Ph

PPh2

2+

2ClO 4-

R R=

N

N

N

1

2

3

Scheme 1. PtAu2 complexes 1−3 with different positioned acetylide ligands.

RESULTS AND DISCUSSION


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Compounds 1−3 (Scheme 1) were readily prepared by mixing [Au(tht)2](ClO4), dpmp and Pt(PPh3)2(C≡CR)2 in 2 : 2 : 1 molar ratio with stirring at ambient temperature for 4 h. The products were purified by silica gel column chromatography to afford compounds 1−3 in high yields (80%−85%). The synthetic procedures of these PtAu2 cluster complexes are much more convenient and efficient than many mononuclear cyclometalated platinum(II) complexes accessed by multistep reactions in harsh conditions.13-25 The formation of doubly µ3-dpmpsupported PtAu2 heteronuclear array involves the substitution of Pt-bound PPh3 with bridging dpmp, concomitant with the incorporation of two AuI ions. Compounds 1−3 are highly soluble in chlorinated solvents such as CH2Cl2 and CHCl3. The corresponding thermogravimetric studies revealed no thermal degradation up to 240 °C (Figure S1). The structure of compound 1⋅E2O was determined by X-ray crystallography. The cationic PtAu2 structure (Figure 1a) is supported by doubly bridging dpmp with the central and terminal P donors bound to platinum(II) and gold(I) atoms, respectively. The Au-Pt-Au backbone is linear with Pt-Au distance of 2.9518(15) Å, which is much shorter than the sum of Van der Waals radii for Pt and Au atoms (3.38 Å) and suggests a significant intermetallic contact. The PtAu2 structure is stabilized by the formation of four five-membered coordination rings as well as significant Pt-Au interactions. The dpmp adopts µ3-η1-bridging mode to support linear-arranged Au-Pt-Au backbone instead of formation six-membered coordination ring Pt(η2-PCH2PCH2P-) through η2-chelation.32,33 The platinum(II) center is coordinated by two trans-oriented σacetylide C and two P donors with an approximately square-planar geometry, while the gold(I) center is bound to two P donors with a P-Au-P angle of 175.13(13)°. Noticeably, the phenyl rings of adjacent PtAu2 moieties show parallel and face-to-face arrangements with 3.79−3.87 Å


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distances between the centers of phenyl rings, implying that significant intermolecular π−π contacts are likely operating as depicted in Figure 1b.

Figure 1. (a) ORTEP drawing (30% thermal ellipsoids) of PtAu2 complex cation of 1. Phenyl rings on phosphorus atoms are omitted for clarity. (b) A crystal packing scheme showing intermolecular π-π stacking between adjacent phenyl rings.

The UV-Vis absorption spectra of compounds 1−3 (Figure 2a) exhibit intense UV absorption bands below 340 nm, due mainly to the dpmp-centered π→π* transitions. A band centered at 350−380 nm with moderate intensity is ascribed to the π→π* transition involving 9-


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phenylcarbazole-acetylide ligand. More importantly, compounds 1−3 show low-energy bands centered at 452, 468 and 395 nm, respectively, resulting most likely from 9-phenylcarbazoleacetylide to platinum(II) LMCT (ligand-to-metal charge transfer) as well as 9-phenylcarbazoleacetylide to dpmp LLCT (ligand-to-ligand charge transfer) transitions.

Table 1: Luminescence Data of Compounds 1−3 in CH2Cl2 Solutions, Powders and PMMA Films at Ambient Temperature.a compound

λem [nm] /τem [µs] /Φem [%] b CH2Cl2

powder

film c

1

535 / 4.01 / 89.3 (43.3)

546 / 2.91 / 32.3 (22.3)

531 /2.42 / 85.4 (78.5)

2

568 / 3.64 / 77.1 (47.9)

568 / 2.49 / 19.6 (18.2)

548 / 2.56 / 72.3 (65.8)

3

523 / 3.09 / 62.1 (33.6)

534 / 2.33 / 12.0 (11.2)

517 / 3.52 / 52.7 (40.2)

a

The measurements were performed at argon atmosphere. b The quantum yields in parentheses were measured in aerated condition. c Doped in PMMA with 6% weight percentage of PtAu2 complexes.

Upon excitation at > 300 nm, compounds 1−3 (Table 1) emit brilliant luminescence at ambient temperature in both fluid solutions and powder states with emissive lifetimes spanning the range of several microseconds. The emission spectra of 1−3 are centered at 535, 568 and 523 nm with quantum yields of 89.3%, 77.1% and 62.1%, respectively, in argon atmosphere at ambient temperature. Nevertheless, the aerated CH2Cl2 solutions of 1−3 display much lower phosphorescent quantum yields (43.3% for 1, 47.9% for 2 and 33.6% for 3), implying a significant quenching of triplet excited states in dioxygen. Since quasi-linear P-Au-P bonds in PtAu2 species are sufficiently stable in fluid solution, the phosphorescent quantum yields are much higher than those of PtAg2 complexes (Φem < 25%) that display fluxional structures due to


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the formation of labile Ag−acetylide or Ag−OClO3 bonds.31 The emission maximum (Figure 2b) in fluid CH2Cl2 follows a descending order of 568 nm (2) > 535 nm (1) > 523 nm (3), which is in accordance to the trend of low-energy absorption bands. As a result, the emission wavelength and phosphorescent color can be modulated by means of carbazole-acetylide ligands in different positions. With acetylide sited at 3-, 2- and 4-position of 9-phenylcarbazole, the emission in CH2Cl2 solutions shows a gradual blue-shift following 568 nm (2) → 535 nm (1) → 523 nm (3).

-1

1.0

-1

0.8

5

0.6

1.0

(a)

1 2 3

0.4 0.2 0.0 250 300 350 400 450 500 550

Normalized PL Intensity

1.2 ε x 10 (M cm )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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(b)

1 2 3

0.8 0.6 0.4 0.2 0.0 450

500

Wavelength (nm)

550 600 650 Wavelength (nm)

700

750

Figure 2. (a) The UV-Vis absorption spectra of complexes 1−3 in CH2Cl2. (b) The emission spectra of complexes 1−3 in fluid CH2Cl2.

The much lower phosphorescent quantum yields of 1−3 (Table 1) in powder states vs. those in CH2Cl2 solutions are ascribed to significant intermolecular π−π contacts between the phenyl rings of adjacent molecules as revealed by X-ray crystallography mentioned above, thus inducing dramatic quenching of phosphorescent emission due to intermolecular aggregation. On the other hand, when compounds 1−3 are dispersed to PMMA, the phosphorescent emission in doping films is much stronger than that in powder states due to the elimination of intermolecular quenching in a diluted matrix. The PMMA films doped with 6% PtAu2 species (Table 1) show quite intense phosphorescence at argon atmosphere with emissive quantum yields of 85.4%, 72.3%


8

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and 52.7% for compounds 1−3, respectively. Upon measured in aerated condition, the PMMA films of compounds 1−3 display an obviously reduced phosphorescence with the quantum yields decreased to 78.5%, 65.8% and 40.2%, respectively, because the phosphorescent emission with triplet excited state can be significantly quenched by dioxygen upon excitation under UV light. The lower phosphorescent quantum yield for the film of 3 vs. those of 1 and 2 is probably ascribed to the lowered absorptivity of the low-energy band for 3 (395 nm) than that for 1 (452 nm) and 2 (468 nm) as shown in Figure 2a. The energy levels and HOMO and LUMO plots of compounds 1−3 in triplet states are shown in Figure 3. The HOMO resides mostly on 9-phenylcarbazole-acetylide (79.72%−89.59% in ground state and 79.89%−89.21% in triplet excited state) with some population at Pt center (16.71%−6.04% in ground state and 16.40%−6.39% in triplet excited state). The LUMO focuses mainly on both dpmp (48.60%−54.02% in ground state and 43.78%−49.96% in triplet excited state) and PtAu2 centers (38.43%−47.45% in ground state and 42.24%−52.45% in triplet excited state). As a result, electron migration from the HOMO to LUMO is characteristic of [π (phenylcarbazole-acetylide) → π* (dpmp)] LLCT and [π (phenylcarbazole-acetylide) → p/s (PtAu2)] LMCT transitions, mixed with a small portion (< 10%) of PtAu2 centered [d → p/s] character. The calculated HOMO-LUMO gap follows 3.33 eV (2) < 3.48 eV (1) < 3.55 eV (3) in singlet state as well as 3.01 eV (2) < 3.13 eV (1) < 3.20 eV (3) in triplet excited state. As a result, DFT studies provide the rationale to the blue-shift of the low energy absorption peaks, i.e. 468 nm (2) → 452 nm (1) → 395 nm (3) in the UV-Vis spectra as well as the measured emission bands, i.e. 568 nm (2) → 535 nm (1) → 523 nm (3) in the phosphorescence spectra.


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Figure 3. The energy level and HOMO and LUMO plots for complexes 1−3 in the triplet states in CH2Cl2 by TD-DFT method at the PBE1PBE level (isovalue = 0.02).

Figure 4. AFM topographical images (2 µ m × 2 µ m) of light-emitting films formed by spincoating. (a) 8 wt% of PtAu2 complex 1 and (b) 8 wt.% of PtAu2 complex 2 doped in a 2 : 1 mixture of TCTA and OXD-7.

Easy accessibility at mild conditions, high phosphorescent quantum yield, excellent resistance to thermal and irradiation degradation and favorable solubility in organic solvents enable these cationic PtAu2 heterotrinuclear complexes 1−3 as ideal phosphorescent materials for the


10

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fabrication of OLEDs by spin-coating procedure. As shown in Figure 4, atomic-force microscope (AFM) images show that the surface roughness of doping films is 0.31 nm for complex 1 (Figure 4a), 0.46 nm for complex 2 (Figure 4b) and 0.31 nm for complex 3 (Figure S6). It appears that doping of PtAu2 species (8%) to the blended host materials of TCTA and OXD-7 in a 2 : 1 ratio could give rise to the uniform films, which warrants the feasibility of device fabrication through solution process. (b)

1 2 3

Normalized EL

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


400

450

500 550 600 Wavelength (nm)

650

700

Figure 5. (a) The energy level diagrams in devices. (b) The electroluminescent spectra of complexes 1−3.

With the availability of the high-quality light-emitting layers, three-layer OLEDs were fabricated and device performances were progressively improved by choosing adequate holetransport and electron-transport host materials, modifying doping percentages of PtAu2 species, and using different electron-transport/hole-blocking layers. The use of whether TCTA or OXD-7 as a single host material resulted in inferior device performance (Figures S7 and S8). Nevertheless, when hole-transport TCTA was blended with electron-transport OXD-7 in 2 : 1 ratio, the devices gave superior performance due to much improved carrier (hole and electron) balance. A dependence of external quantum efficiency (EQE) and luminance vs doping weight


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percentage of PtAu2 complex 1 is plotted in Figure S9, indicating that the use of 8 wt.% of PtAu2 complex afforded the best device performance.

Table 2. The Performance Data of Solution-Processed OLEDs Based on PtAu2 Complexes 1− −3. 1

2

3

Ir(mppy)3 b

λEL [nm]

532

547

517

514, 536(sh)

Von a [V]

4.7

4.5

5.0

2.8

Lmax [cd cm-2]

24408

32915

7356

44172

CEmax [cd A-1]

78.2

78.3

30.0

66.8

CE [cd A-1] at 102 cd m-2

24.2

75.6

27.7

20.8

CE [cd A-1] at 103 cd m-2

77.8

74.6

25.6

54.4

PEmax [lm W-1]

26.4

40.4

12.5

40.1

PE [lm W-1] at 102 cd m-2

9.9

32.3

12.1

18.2

PE [lm W-1] at 103 cd m-2

26.4

25.5

9.6

39.8

EQEmax [%]

21.5

20.2

10.1

18.1

EQE [%] at 102 cd m-2

6.7

19.5

9.3

5.6

EQE [%] at 103 cd m-2

21.4

19.3

8.6

14.8

CIE

0.28, 0.68

0.38, 0.60

0.21, 0.40

0.19, 0.54

Turn-on voltage at 1 cd m-2. b Device structure is ITO / spin-coated PEDOT : PSS / spin-coated CBP (61%) : TPD (9%) : PBD (24%) : Ir(mppy)3 (6%) / thermally evaporated BPhen (40 nm) / LiF (1 nm) / Al (100 nm). a

The electroluminescence data of compounds 1−3 is summarized in Table 2, based on the threelayer device configuration ITO / PEDOT : PSS (50 nm) / TCTA & OXD-7 : 8 wt.% PtAu2


12

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complex (50 nm) / TPBi (50 nm) / LiF (1 nm) / Al (100 nm). The energy level diagrams and electroluminescent spectra of 1−3 are depicted in Figure 5. The electroluminescence spectra show the emission maximum at 532 nm for 1, 547 nm for 2 and 517 nm for 3, coinciding perfectly with the photoluminescent spectra centered at 531 m for 1, 548 nm for 2 and 517 nm for 3 in doped films. Hence, the electroluminescent spectra show a gradual blue-shift following 547 nm (2) → 532 nm (1) → 517 nm (3) to give green, yellow-green and bluish green emission, respectively. Therefore, it is viable to modulate electroluminescence and to achieve different colors for cationic PtAu2 complexes with different positioned 9-phenylcarbazole-acetylide ligands. Current density-voltage-luminance characteristics and current efficiency/external quantum efficiency vs luminance are shown in Figure 6 (complex 1) and Figure 7 (complex 2) and Figure S11 (complex 3). The turn-on voltage and the largest current efficiency (CE), power efficiency (PE) and external quantum efficiency (EQE) for the device of complex 1 are 4.7 V, 78.2 cd A-1, 26.4 lm W-1 and 21.5%, respectively, at a practical luminance of 1029 cd m-2. At the brightness of 5000 cd m-2, the CE is 62.1 cd A-1 and the EQE is 17.1% with ca. 20% efficiency roll-off. This represents one of the best performances for solution-processed OLEDs, which is comparable to the state-of-the-art phosphorescent OLEDs based on neutral cyclometallated iridium(III) complexes,34,35 but better than those based on binuclear copper(I) complexes (the CE is only 47 ± 2 cd A-1 at a practical luminance of 1000 cd m-2).36 In order to make a direct comparison with state-of-the-art solution-processed OLEDs based on Ir(mppy)3 (mppy = 2-(ptolyl)pyridine), we reproduced the device by the reported procedure,34 making use of device structure ITO / spin-coated PEDOT : PSS / spin-coated CBP (61%) : TPD (9%) : PBD (24%) : Ir(mppy)3 (6%) / thermally evaporated BPhen (40 nm) / LiF (1 nm) / Al (100 nm). As shown in


13


Table 2 and Figure S12 (Supplementary Information), the measured turn-on voltage (2.8 V) and peak current efficiency (66.8 cd A-1) accord well with those (2.8 V and 69 cd A-1) described in literature.34 For complex 2, the turn-on voltage and the largest CE, PE and EQE are 4.5 V, 78.3 cd A-1, 40.4 lm W-1 and 20.2%, respectively. At the practical brightness of 1000 cd m-2, the CE is 74.6 cd A-1 and the EQE is 19.3%. The efficiency roll-off is 22% at the brightness of 5000 cd m-2. Comparatively, the device performance for 3 is obviously inferior to that for 1 and 2, in which the highest CE, PE and EQE are only 30.0 cd A-1, 12.5 lm W-1 and 10.1%, respectively. The poor efficiency for 3 can be rationalized by the lower phosphorescent quantum yield in doped film of

4

Current Density Luminance

100

100

10

3

10

80 60

10

40

1

10

20

0

0

10

0

2

4

6 8 10 Voltage (V)

12

14

16

(b)

80

15

60 40

Current Efficiency EQE

20 0

20

10

EQE (%)

2

Current Efficiency (cd/A)

2

(a)

120

2

Current Density (mA/cm )

3 than that of 1 or 2.

Luminance (cd/m )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 25

5

0 2000 4000 6000 8000 10000 2 Luminance (cd/m )

Figure 6. (a) Current density-voltage-luminance characteristics. (b) Current efficiency/external quantum efficiency vs luminance for OLED based on complex 1.


14

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10

3

10

100

2

10 50

1

10

0

0

10 0

2

4

6 8 10 12 14 16 Voltage (V)

(b)

20

80 15

60 40

Current Efficiency EQE

20

10

EQE (%)

Current Density Luminance

Current Efficiency (cd/A)

2

150

4

2

Current Density (mA/cm )

100 (a)

Luminance (cd/m )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


5

0 2000 4000 6000 8000 10000 2 Luminance (cd/m )

Figure 7. (a) Current density-voltage-luminance characteristics. (b) Current efficiency/external quantum efficiency vs luminance for OLED based on complex 2.

CONCLUSIONS Three cationic PtAu2 cluster complexes with different positioned 9-phenylcarbazole-acetylide ligands were employed to modulate their phosphorescent properties. With acetylide bound to 9phenylcarbazole in 3-, 2- and 4-position, both photoluminescent and electroluminescent spectra show a progressive blue-shift. Making use of 8 wt% PtAu2 complex doped in the 2 : 1 mixture of TCTA and OXD-7 as the emitting layers, solution-processed OLEDs gave superior electroluminescence. The maximum CE and EQE of the devices for PtAu2 complexes 1, 2 and 3 are recorded to be 78.2 cd A-1 and 21.5%, 78.3 cd A-1 and 20.2%, and 30.0 cd A-1 and 10.1%, affording green, yellow-green and bluish green electroluminescence, respectively. We conclude that PtAu2 cluster complexes are comparable to mononuclear cyclometallated platinum(II) or iridium(III) complexes for achieving high-efficiency OLEDs through solution process. The use of carbazole-functionalized acetylide ligands for the design of phosphorescent emitters is a viable approach to modulate both electroluminescent color and efficiency.

MATERIALS AND METHODS


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Synthesis of [PtAu2(dpmp)2(C≡ ≡C-2-Phcarb-9)2](ClO4)2 (1). To a CH2Cl2 (20 mL) solution of [Au(tht)2](ClO4) (47.3 mg, 0.1 mmol) was added dpmp (50.6 mg, 0.1 mmol) with stirring for 30 min. When Pt(PPh3)2(C≡C-2-Phcarb-9)2 (62.5 mg, 0.05 mmol) was added, the solution changed to yellow-green upon stirring at ambient temperature for 4 h. The product was then purified by chromatography on a silica gel column using CH2Cl2-MeCN (8 : 1) as eluent to give a yellowgreen solid. Yield: 83%. Anal. Calcd for C104H82Au2Cl2N2O8P6Pt: C, 53.53; H, 3.54; N, 1.20. Found: C, 53.86; H, 3.62; N, 1.28. ESI-MS m/z (%): 2233.1 (100) [M-ClO4]+, 1066.5 (28) [M2ClO4]2+. 1H NMR (CD2Cl2, ppm): 8.18-8.14 (d, 2H, J = 7.9 Hz), 7.96-7.92 (d, 2H, J = 7.9 Hz), 7.87-7.79 (m, 6H), 7.78-7.66 (m, 10H), 7.65-7.48 (m, 18H), 7.47-7.41 (t, 6H, J = 7.4 Hz), 7.397.29 (m, 6H), 7.28-7.21 (m, 4H), 7.20-7.06 (m, 6H), 7.01-6.95 (t, 4H, J = 7.8 Hz), 6.91-6.78 (m, 6H), 6.67-6.61 (t, 4H, J = 7.6 Hz), 5.58-5.43 (m, 4H), 4.38-4.30 (m, 4H).

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P NMR (CD2Cl2,

ppm): 31.0 (m, 4P, JP-P = 31.1 Hz), 5.5 (m, 2P, JP-P = 30.6 Hz, JPt-P = 2644 Hz). IR (KBr, cm-1): 2102w (C≡C), 1099s (ClO4-). Synthesis of [PtAu2(dpmp)2(C≡ ≡C-3-Phcarb-9)2](ClO4)2 (2). This compound was prepared by the same synthetic procedure as that of 1 except for the use of 3-ethynyl-9-phenylcarbazole (HC≡C-3-Phcarb-9) in place of 2-ethynyl-9-phenylcarbazole. Yield: 85%. Anal. Calcd for C104H82Au2Cl2N2O8P6Pt⋅1/2CH2Cl2: C, 52.82; H, 3.52; N, 1.18. Found: C, 52.76; H, 3.37; N, 1.24. ESI-MS m/z (%): 2233.4 (100) [M-ClO4]+, 1067.2 (46) [M-2ClO4]2+. 1H NMR (CD2Cl2, ppm): 8.04-7.90 (m, 10H), 7.75-7.65 (m, 12H), 7.64-7.57 (m, 18H), 7.55-7.51 (m, 10H), 7.477.40 (m, 12H), 7.30-7.24 (t, 4H, J = 7.9 Hz), 7.14-7.07 (t, 6H, J = 7.3 Hz), 6.86-6.80 (m, 2H), 5.48-5.34 (m, 4H), 4.63-4.47 (m, 4H). 31P NMR (CD2Cl2, ppm): 31.2 (m, 4P, JP-P = 30.3 Hz), 6.0 (m, 4P, JP-P = 30.2 Hz, JPt-P = 2562 Hz). IR (KBr, cm-1): 2098w (C≡C), 1100s (ClO4-).


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Synthesis of [PtAu2(dpmp)2(C≡ ≡C-4-Phcarb-9)2](ClO4)2 (3). This compound was prepared by the same synthetic procedure as that of 1 except for the use of 4-ethynyl-9-phenylcarbazole (HC≡C-4-Phcarb-9) in place of 2-ethynyl-9-phenylcarbazole. The product was recrystallized by layering n-hexane onto CH2Cl2 solution. Yield: 80%. Anal. Calcd for C104H82Au2Cl2N2O8P6Pt: C, 53.53; H, 3.54; N, 1.20. Found: C, 53.83; H, 3.62; N, 1.08. ESI-MS m/z (%): 2233.3 (100) [MClO4]+, 1067.1 (37) [M-2ClO4]2+. 1H NMR (CD2Cl2, ppm): 8.11-8.05 (d, 2H, J = 8.0 Hz), 7.867.80 (m, 8H), 7.70-7.65 (m, 10H), 7.44-7.38 (m, 18H), 7.37-7.30 (m, 20H), 6.96-6.86 (m, 10H), 6.60-6.53 (t, 4H, J = 7.5 Hz), 6.52-6.48 (s, 2H), 5.23-4.98 (m, 4H), 4.14-4.00 (m, 4H). 31P NMR (CD2Cl2, ppm): 31.5 (m, 4P, JP-P = 31.5 Hz), 3.91 (m, 2P, JP-P = 30.4 Hz, JPt-P = 2507 Hz). IR (KBr, cm-1): 2102w (C≡C), 1101s (ClO4-). Device Fabrication and Characterization. ITO substrates were cleaned by sonication in deionized water, acetone, and isopropanol followed by UV-ozone treatment for 15 min. PEDOT : PSS solution was filtered through a 0.22μm filter and spin-coated at 3000 rpm on the precleaned substrates, and dried at 140 °C for 20 min to give a film of 50 nm thickness. The emitting layer was spin-coated at 1500 rpm using a filtered CH2Cl2 solution (5.5 mg/mL) of blended host and PtAu2 species. Subsequently, 50 nm thickness of TPBi, 1 nm thickness of LiF and 100 nm thickness of Al were thermally deposited in an inert chamber at a base pressure less than 4 × 10−4 Pa. The electroluminescence (EL) spectra were recorded on an Edinburgh FLS-920 spectrometer. The current density-voltage-brightness (I-V-B) curves of the devices were recorded on a Keithley 2400/2000 source meter and a calibrated silicon photodiode. All measurements of the devices were carried out under ambient conditions.

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Supporting Information. Tables and figures giving additional structural, photophysical, computational and device performance data, and X-ray crystallographic file in CIF format for the determination of the structure of 1·Et2O. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author E-mail: [email protected] (Z.-N. C), [email protected] (Y. C.) Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was support by the 973 project from MSTC (2014CB845603), the NSF of China (21390392, 21473201, U1405252, 21531008 and 21303204), the Natural Science Foundation of Fujian Province (2013J05036), the CAS/SAFEA International Partnership Program for Creative Research Teams, and the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB20000000).

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Phosphorescent PtAu2 Complexes with Differently Positioned

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