Phosphorescent Iridium(III) Complexes Bearing Fluorinated Aromatic

Subscriber access provided by University of Otago Library

Article

Phosphorescent Iridium(III) Complexes Bearing Fluorinated Aromatic Sulfonyl Group with Nearly Unity Phosphorescent Quantum Yields and Outstanding Electroluminescent Properties Jiang Zhao, Yue Yu, Xiaolong Yang, Xiaogang Yan, Huiming Zhang, Xianbin Xu, Guijiang Zhou, Zhaoxin Wu, Yixia Ren, and Wai-Yeung Wong ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.5b07177 • Publication Date (Web): 12 Oct 2015 Downloaded from http://pubs.acs.org on October 20, 2015

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 37

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

ACS Applied Materials & Interfaces

Phosphorescent Iridium(III) Complexes Bearing Fluorinated Aromatic Sulfonyl Group with Nearly Unity Phosphorescent Quantum Yields and Outstanding Electroluminescent Properties Jiang Zhao,† Yue Yu,‡ Xiaolong Yang,† Xiaogang Yan,† Huiming Zhang,† Xianbin Xu,† Guijiang Zhou,*,† Zhaoxin Wu,*, ‡ Yixia Ren,*,† and Wai-Yeung Wong*, ¶, ⊥

†

MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter,

State Key Laboratory for Mechanical Behavior of Materials, Institute of Chemistry for New Energy Material, Department of Chemistry, Faculty of Science, Xi’an Jiaotong University, Xi’an 710049, P. R. China. ‡

Key Laboratory of Photonics Technology for Information, School of Electronic and

Information Engineering, Xi’an Jiaotong University, Xi’an, 710049, P. R. China ¶

Institute of Molecular Functional Materials, Department of Chemistry and Institute of

Advanced Materials, Hong Kong Baptist University, Hong Kong, P. R. China. ⊥

HKBU Institute of Research and Continuing Education, Shenzhen Virtual University Park,

Shenzhen, 518057, P. R. China

1

ACS Paragon Plus Environment


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

ABSTRACT: A series of heteroleptic functional IrIII complexes bearing different fluorinated aromatic sulfonyl groups has been synthesized. Their photophysical features, electrochemical behaviors and electroluminescent (EL) properties have been characterized in detail. These complexes emit intense yellow phosphorescence with exceptionally high quantum yields (ΦP > 0.9) at room temperature, the emission maxima of which can be finely tuned depending upon the number of the fluorine substituents on the pendant phenyl ring of the sulfonyl group. Furthermore, the electrochemical properties and electron injection/transporting (EI/ET) abilities of these IrIII phosphors can also be effectively tuned by the fluorinated aromatic sulfonyl group to furnish some desired characters for enhancing the EL performance. Hence, the maximum luminance efficiency (ηL) of 81.2 cd A−1, corresponding to power efficiency (ηP) of 64.5 lm W−1 and external quantum efficiency (ηext) of 19.3%, has been achieved, indicating the great potential of these novel phosphors in the field of organic light-emitting diodes (OLEDs). Furthermore, a clear picture has been drawn for the relationship between their optoelectronic properties and chemical structures. These results should provide important information for developing highly efficient phosphors. KEYWORDS: iridium complexes, OLEDs, sulfonyl group, electron injection/transporting, fluorination, functionalization

2


Page 2 of 37

Page 3 of 37

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


INTRODUCTION Recently, aromatic sulfonyl groups have received much interest in the field of organic lighting-emitting diodes (OLEDs) owing to their inherent electronic features.1-5 According to their chemical structures, sulfonyl groups can show the potential of furnishing electron injection/transporting (EI/ET) abilities to the concerned organic semiconductors which would improve the electroluminescent (EL) performances of the concerned OLEDs.1,5,6 Representing one the revolutionary advances in OLEDs, phosphorescent (triplet) emitters have substantially improved the EL efficiencies of OLEDs by employing both singlet and triplet excitons for the EL process.7-12 However, the phosphorescent emitters should be doped into a host material at a low doping level, typically less than 10 wt %, in order to fabricate OLED devices to avoid exciton quenching problem due to their relatively long lifetime in the order of microsecond. Based on the working mechanism of OLEDs, charge carrier injection/transporting abilities together with the balanced charge injection/transport for both kinds of charge carriers of the host materials are very crucial to the EL performances of phosphorescent OLEDs (PHOLEDs).9,13 Owing to their good electron injection/transporting (EI/ET) abilities, aromatic sulfonyl groups should be attractive building blocks for constructing host materials in PHOLEDs. Hence, some novel host materials with phenylsulfonyl groups have been developed to make highly efficient PHOLEDs through enhancing the EI/ET properties of the concerned hosts.2-4 Furthermore, by combining aromatic sulfonyl groups with triphenylamine (TPA) group, novel host materials with ambipolar features have be prepared to fulfill balanced charge carrier injection/transporting in PHOLEDs by taking advantages of both hole injection/transporting (HI/HT) ability of the TPA group and EI/ET ability of the aromatic sulfonyl groups.5 Apart from being introduced to the host materials, aromatic sulfonyl groups have been 3



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

employed to develop functionalized phosphorescent emitters with unique electronic features. In our previous reports,1,14-16 the phenylsulfonyl group has been attached to the 2-phenylpyridine (ppy) ligand of the IrIII and PtII complexes to develop novel functionalized phosphorescent emitters with EI/ET characters. Benefiting from their EI/ET ability, the ppy-type IrIII phosphorescent emitters can furnish attractive EL efficiencies in both monochromatic and white OLEDs.1,6,14-16 In addition, ppy-type ligands bearing phenylsulfonyl group have been employed to synthesize novel asymmetric IrIII phosphorescent emitters with either EI/ET behaviors or ambipolar features, which can give very high EL efficiencies to the concerned PHOLEDs.17,18 All these encouraging EL performances achieved have clearly indicated that aromatic sulfonyl groups can show great potential in developing novel materials for highly efficient OLEDs. Clearly, the advantages associated with the aromatic sulfonyl groups should come from their good EI/ET ability, which is more preferable over the HI/HT features because organic semiconductors typically exhibit much higher HI/HT ability.19 Hence, organic semiconductors with good EI/ET ability are more desirable to fulfill balanced charge carrier injection/transport in OLEDs. Accordingly, developing functional materials with good EI/ET ability should represent a very important research area in the field of OLEDs. However, for the time being, functional materials with aromatic sulfonyl groups are still limited in number.1-6,14-16 Considering the great potential afforded by the aromatic sulfonyl groups, developing more EL materials with these groups should be very important for promoting the development of the OLEDs. Bearing this in mind, a series of ppy-type IrIII phosphorescent emitters bearing aromatic sulfonyl groups has been developed by employing different fluorophenyl moieties. All these phosphorescent emitters not only show exceptional phosphorescent quantum yields (ΦP) close to 100%, but also furnish very decent EL performances afforded by their EI/ET ability. In this 4


Page 4 of 37

Page 5 of 37

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


contribution, it provides a very simple strategy to optimize EI/ET properties of the IrIII phosphorescent emitters with great potential for practical application in the field of OLEDs.

EXPERIMENTAL SECTION General Information. All commercially available starting materials were used directly with no further purification. The solvents were carefully dried prior to use. All reactions were monitored using thin-layer chromatography (TLC) purchased from Merck & Co., Inc. Flash column chromatography and preparative TLC were made from silica gel bought from Shenghai Qingdao (300-400 mesh). 1H, 13C and 19F NMR spectra were recorded in CDCl3 on a Bruker Avance 400 MHz spectrometer and chemical shifts were referenced to the solvent residual peak at δ 7.26 ppm for 1H and 77.0 ppm for 13C, respectively. Elemental analyses were performed on a Flash EA 1112 elemental analyzer. The thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) data were collected on a NETZSCH STA 409C instrument and a NETZSCH DSC 200 PC unit, respectively. UV-vis absorption spectra were measured at room temperature on a Shimadzu UV-2250 spectrophotometer. Emission spectra and lifetimes of these compounds were recorded on an Edinburgh Instruments Ltd (FLSP920) fluorescence spectrophotometer using the software package provided by Edinburgh Instruments. The phosphorescent quantum yields (ΦP) were determined in CH2Cl2 solutions at 293 K against fac-[Ir(ppy)3] (ΦP = 0.40). The ΦP of the phosphorescent complexes in doped CBP film (10 wt%) obtained by vacummn deposition on quartz substrate was measured in a integration sphere associated with FLSP920 fluorescence spectrophotometer. Cyclic voltammetry was performed using a Princeton Applied Research model 273A potentiostat at a scan rate of 100 mV s-1. All experiments were carried out in a three-electrode compartment cell with a Pt-sheet counter electrode, a glassy carbon working 5



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

electrode, and a Ag/AgCl reference electrode. The supporting electrolyte used was 0.1 M [nBu4N]BF4 solution in acetonitrile. Fast atom bombardment (FAB) mass spectra were recorded on a Finnigan MAT SSQ710 system. The surface morphology for the doped films is obtained on the Dimension3000 Atomic Force Microscope, Digital Instrument. X-ray Crystallography. Single crystal of IrS-5F of suitable dimensions was mounted in thin glass fiber for collecting the intensity data on a Bruker SMART CCD diffractometer (Mo Kα radiation and λ = 0.71073 Å) in Φ and ω scan modes at 293 K. The structure was solved by direct methods followed by difference Fourier syntheses and then refined by full-matrix least-squares techniques against F2 using SHELXL-9720 program on a personal computer. The positions of hydrogen atoms were calculated and refined isotropically using a riding model. All other non-hydrogen atoms were refined isotropically. Absorption corrections were applied using SADABS.21 Computational Details. Geometrical optimizations were conducted using the popular B3LYP density functional theory (DFT). The basis set used for C, H, O, N, F and S atoms was 6-311G(d, p), whereas effective core potentials with a LanL2DZ basis set were employed for Ir atom.22,23 The energies of the excited states of the complexes were computed by TD-DFT based on all the ground-state geometries. All calculations were carried out by using the Gaussian 09 program.24 General Procedure for the Synthesis of the Ligands with Sulfonyl Group. Under a N2 atmosphere, the corresponding bromo(fluorophenylsulfonyl)benzene compound (1.0 equiv) and 2-(tributylstannyl)pyridine (1.0 equiv) were mixed in toluene. Then, Pd (PPh3)4 (0.05 equiv) was added as a catalyst for the Stille cross-coupling reaction. The reaction was allowed to proceed at 110 °C for 16 h. After cooling to room temperature, the solvent was removed under reduced pressure. The dark residue was purified by silica gel column chromatography eluting with 6


Page 6 of 37

Page 7 of 37

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


CH2Cl2. LS-1F (Yield: 85%) 1H NMR (400 MHz, CDCl3): δ (ppm) 8.72(m,1H), 8.15 (s, 1H), 8.13 (d, J = 1.6 Hz,1H), 8.03–7.96 (m, 4H), 7.82–7.74 (m, 2H), 7.33–7.29 (m, 1H), 7.20–7.17 (m, 2H); 13

C NMR (100 MHz, CDCl3): δ (ppm) 155.24, 150.05, 144.14, 141.39, 137.04, 130.51, 130.42,

128.08, 127.81, 123.32, 121.06, 116.73, 116.51; 19F NMR (376 MHz, CDCl3)：δ (ppm) -104.09 (s, 1F); FAB-MS (m/z): 313 [M] +; Anal. Calcd. for C17H12FNO2S: C, 65.16; H, 3.86; N, 4.47; found: C, 64.93; H, 3.68; N, 4.12%. LS-2F (Yield: 86%) 1H NMR (400 MHz, CDCl3): δ (ppm) 8.73 (d, J = 4.4 Hz,1H), 8.17–8.13 (m, 3H), 8.10 (d, J = 8.4 Hz, 2H), 7.81–7.76 (m,2H), 7.33–7.30 (t, J = 5.2 Hz,1H), 7.08–7.04 (t, J = 7.6 Hz, 1H), 6.89–6.84 (t, J = 8.4 Hz,1H); 13C NMR (100 MHz, CDCl3): δ (ppm) 167.83, 165.26, 161.40, 158.82, 155.18, 150.03, 144.56, 140.58, 137.03, 131. 65, 128.55, 123.35, 121.11, 112.27, 106.09, 105.83; 19F NMR (376 MHz, CDCl3): δ (ppm) -98.97 (d, 1F), -102.27 (d, 1F); FAB-MS (m/z): 331 [M] +; Anal. Calcd. for C17H11F2NO2S: C, 61.62; H, 3.35; N, 4.23; found: C, 61.35; H, 3.43; N, 3.98%. LS-3F (Yield: 90%) 1H NMR (400 MHz, CDCl3): δ (ppm) 7.82 (d, J = 4.4 Hz, 1H), 8.18 (d, J = 8.4 Hz, 2H), 8.02 (d, J = 8.4 Hz, 2H), 7.83–7.75 (m, 2H), 7.63 (t, J = 6.4 Hz, 2H), 7.33–7.30 (m,1H); 13C NMR (100 MHz, CDCl3): δ (ppm) 154.85, 150.09, 144.81, 139.91, 137.09, 128.32, 128.03, 123.50, 121.11, 112.94, 112.87, 112.78, 112.70; 19F NMR (376 MHz, CDCl3): δ (ppm) -128.83 (d, 2F), -150.62 (t, 1F); FAB-MS (m/z): 349 [M] +; Anal. Calcd. for C17H10F3NO2S: C, 58.45; H, 2.89; N, 4.01; found: C, 68.27; H, 2.71; N, 3.89%. LS-5F (Yield: 83%) 1H NMR (400 MHz, CDCl3): δ (ppm) 8.75 (d, J = 4.8 Hz,1H), 8.23–8.15 (m, 4H), 7.85–7.78 (m, 2H), 7.36–7.33 (m, 1H); 13C NMR (100 MHz, CDCl3): δ (ppm) 154.83, 150.17, 7



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

145.98, 145.63, 143.51, 143.38, 140.52, 139.23, 137.13, 128.36, 128.00, 123.62, 121.21;

Page 8 of 37

19

F

NMR (376 MHz, CDCl3): δ (ppm) -135.27 – -135.40 (m, 2F), -143.68 – -143.83 (m, 1F), -157.93 – -158.09 (m, 2F); FAB-MS (m/z): 385 [M] +; Anal. Calcd. for C17H8F5NO2S: C, 52.99; H, 2.09; N, 3.64; found: C, 62.83; H, 1.94; N, 3.39%. General Procedure for the Synthesis of the Phosphorescent Complexes. Under a N2 atmosphere, the corresponding organic ligand (2.2 equiv) and IrCl3·nH2O (1.0 equiv, 60 wt % Ir content) were heated to 110 °C in a mixture of 2-ethoxyethanol and water (3:1, v/v) for 16 h. Then, the reaction mixture was cooled to room temperature and water was added. The cyclometalated IrIII µ-chlorobridged dimer was formed as a precipitate which was collected and dried under vacuum. The IrIII µ-chloro-bridged dimer, acetylacetone (5.0 equiv) and Na2CO3 (10.0 equiv) were added to 2-ethoxyethanol and the mixture was heated to 110 °C for 15 h. After cooling to room temperature and the addition of water, the colored precipitate was collected by filtration and washed with water and dried. The crude product was purified on a silica gel column using CH2Cl2 as eluent to obtain the pure sample as an orange solid. IrS-1F (Yield: 58%) 1H NMR (400 MHz, CDCl3): δ (ppm) 8.47 (d, J = 5.6 Hz, 2H), 7.92–7.85 (m, 4H), 7.60–7.56 (m, 6H), 7.33–7.28(m, 4H,), 7.02–7.96 (m, 4H), 6.54 (d, J = 2.0Hz, 2H), 5.26 (s, 1H), 1.83 (s, 6H);

13

C NMR (100 MHz, CDCl3): δ (ppm) 185.07, 166.33, 163.77,

149.77, 148.66, 147.71, 139.73, 137.87, 130.68, 130.20, 123.82, 123.42, 120.07, 119.86, 116.15, 115.93, 100.72, 28.59; 19F NMR (376 MHz, CDCl3): δ (ppm) -105.09 (s, 2F); FAB-MS (m/z): 916 [M]+; Anal. Calcd. for C39H29F2IrN2O6S2: C, 51.14; H, 3.19; N, 3.06; found: C, 50.93; H, 3.01; N, 2.93%. IrS-2F (Yield: 53%) 1H NMR (400 MHz, CDCl3): δ (ppm) 8.50 (d,J = 5.2 Hz, 2H), 7.92–7.87 (m, 4H), 7.83–7.78 (m, 2H), 7.59 (d, J = 8.4 Hz, 2H), 7.35–7.31 (m, 4H), 6.91–6.87 (m, 2H), 8


Page 9 of 37

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


6.64–6.59 (m, 4H), 5.28 (s, 1H), 1.80 (s, 6H); 13C NMR (100 MHz, CDCl3): δ (ppm) 185.05, 166.31, 150.34, 148.67, 147.34, 138.96, 137.84, 131.37, 131.27, 131.10, 123.65, 123.53, 120.39, 119.95, 111.69, 111.44, 105.52, 100.73, 28.62; 19F NMR (376 MHz, CDCl3): δ (ppm) -100.23 (d, 2F), -102.21 (d, 2F); FAB-MS (m/z): 952 [M]+; Anal. Calcd. for C39H27F4IrN2O6S2: C, 49.20; H, 2.86; N, 2.94; found: C, 49.01; H, 2.95; N, 2.85%. IrS-3F (Yield: 62%) 1H NMR (400 MHz, CDCl3): δ (ppm) 8.50 (d, J = 5.2 Hz, 2H), 7.97–7.91 (m, 4H), 7.62 (d, J = 8.0 Hz, 2H), 7.39–7.36 (m, 2H), 7.30–7.28 (m, 2H), 7.25–7.19 (m,2H), 6.46 (d, J = 1.6 Hz, 2H), 5.28 (s, 1H), 1.81 (s, 6H);

13

C NMR (100 MHz, CDCl3): δ (ppm)

185.19, 166.05, 152.16, 150.40, 149.60, 148.76, 147.99, 143.91, 141.33, 138.55, 137.96, 130.75, 123.85, 120.30, 112.64, 100.85, 28.59; 19F NMR (376 MHz, CDCl3): δ (ppm) -129.63 (d, 4F), -151.55 (t, 2F); FAB-MS (m/z): 988 [M]+; Anal. Calcd. for C39H25F6IrN2O6S2: C, 47.41; H, 2.55; N, 2.84; found: C, 47.33; H, 2.61; N, 2.72%. IrS-5F (Yield: 66%) 1H NMR (400 MHz, CDCl3): 8.53 (d, J = 4.8 Hz, 2H), 7.98–7.91 (m, 4H), 7.64 (d, J = 8.0 Hz, 2H), 7.42 (t, J = 9.2 Hz, 4H), 6.65 (s, 2H), 5.32 (s, 1H), 1.83 (s, 6H); 13C NMR (100 MHz, CDCl3): δ (ppm) 185.19, 166.80, 151.52, 148.70, 147.88, 145.74, 143.27, 142.89, 139.00, 138.21, 136.37, 130.28, 124.04, 120.28, 117.70, 100.91, 28.59; -135.97 – -136.08 (m, 4F), -144.82 – -144.95 (m, 2F), -158.75 – -158.92 (m, 4F); FAB-MS (m/z): 1060 [M]+; Anal. Calcd. for C39H21F10IrN2O6S2: C, 44.19; H, 2.00; N, 2.64; found: C, 44.00; H, 2.13; N, 2.70%. OLED Fabrication and Measurements. The pre-cleaned ITO glass substrates were treated with ozone for 20 min. The MoO3 was deposited on the surface of ITO to form a 3 nm-thick hole-injection layer. Then, 4,4’-N,N’-dicarbazole-biphenyl (CBP) layer was begun to be deposited. When the CBP layer reached ca. 35 nm, the evaporation source of the IrIII complex 9



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

was opened to form a doped CBP region with a thickness of ca. 20 nm. Then, 1,3,5-tris[N-(phenyl)benzimidazole]-benzene (TPBi) (60 nm), LiF (1 nm) and Al cathode (100 nm) were successively evaporated at a base pressure less than 10–6 Torr. The EL spectra and CIE coordinates were measured with a PR650 spectra colorimeter. The J-V-L curves of the devices were recorded by a Keithley 2400/2000 source meter and the luminance was measured using a PR650 Spectra Scan spectrometer. All the experiments and measurements were carried out under ambient conditions.

RESULTS AND DISCUSSION Synthetic Strategies and Structural Characterization. The chemical structures and detailed synthetic protocols of the IrIII complexes with fluorinated aromatic sulfonyl groups are shown in Scheme 1 and Figure S1 in Supporting Information (SI). As the key compounds, the organic cyclometalating ligands were prepared by Stille cross-coupling of 2-(tributylstannyl)pyridine with the appropriate fluorinated aromatic sulfonyl compounds in high yields. All the heteroleptic complexes were obtained via a two-step procedure. The relevant organic ligands reacted with the metal source IrCl3·nH2O to afford the µ-chloro-bridged precursor complexes, which were then converted into the final complexes by reaction with acetylacetone in the presence of Na2CO3.25 These air-stable compounds were isolated in high purity as orange solids by column chromatography on silica gel with the proper eluent.

10


Page 10 of 37

Page 11 of 37

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


Br

S O

Br

Br

F

O

F

S O

O

O

Br

S O

F

O

F

S O F

F

F S-1F

S-3F F

S-2F

F F

S-5F

F

N Pd(PPh3)4 SnBu3

N

S O

F

O

F

S O

N

N

O

O

N

S O

F S O F L-5F F

O

F F

F L-1F

L-3F F

L-2F

F F

i) IrCl3.nH2O ii) Acetylacetone, Na2CO3

N

N

O Ir

O

O

S O

S O

F

Ir

O

O

2

F

O

2

O

O

S O

2

F

F IrS-1F

N

O

Ir O

2

N

O

Ir

O

F IrS-2F

IrS-3F

F

IrS-5F

F S O F

F F F

III

Scheme 1. Synthetic protocols of the Ir complexes with fluorinated aromatic sulfonyl groups.

The chemical structures of all these new IrIII complexes have been fully characterized with 1H, 13

C and 19F NMR spectra. In their 1H NMR spectra, the resonance signals with chemical shifts at

ca. 5.30 and 1.80 ppm can be assigned to the acetylacetone auxiliary ligands. The other resonance peaks in the low field region come from the ppy-type ligands with fluorinated aromatic sulfonyl groups. The 19F NMR spectra also indicate the expected structural features of 11



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

these IrIII complexes. For IrS-1F, the single resonance peak at ca. -105.09 ppm is induced by the only -F group on the pendant ring of the sulfonyl block. The two sets of signals at ca. -100.23 ppm and -102.21 ppm have clearly indicated the two -F substituents at different position of the fluorinated sulfonyl unit in IrS-2F. Similarly, IrS-3F also exhibits two sets of resonance peaks at ca. -129.63 ppm and -151.55 ppm in its

19

F NMR spectrum, which is consistent with the

fluoro-substitution pattern in IrS-3F. The three sets of resonance peaks with integral ratio of 2:1:2 is also in good agreement with the fluoro-substitution pattern of IrS-5F. Hence, all these spectral data can clearly reveal the chemical structures of these IrIII complexes. Critically, the structure of IrS-5F has been determined by X-ray crystallography (Figure 1). The X-ray data confirmed that the central iridium center was coordinated by two ppy-type cyclometalating ligands and one chelating acac ligand. The coordination around the Ir center is distorted octahedral, with the cis-O,O, cis-C,C, and trans-N,N chelated disposition (Figure 1, Table S1 and S2). The bonds chelating around the Ir atom show typical bond lengths as compared with those observed in similar complexes.1,26

Figure 1. ORTEP drawing of IrS-5F with thermal ellipsoids drawn at 10% probability level. Labels on some atoms are omitted for clarity. 12


Page 12 of 37

Page 13 of 37

Thermal and Photophysical Properties. The thermal properties of these IrIII complexes were characterized by both thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) under a nitrogen flow. The TGA data reveal their good thermal stability with the 5% weight-reduction temperatures (∆T5%) ranging from 309 to 350 oC (Table 1). Analysis of the DSC traces for these complexes indicated their high glass-transition temperature (Tg) in the range from 145 to 165 oC, which is typically desirable for high-performance OLEDs. According to their structural features, the glass-transition process of these IrIII complexes should be induced by the motion of the aromatic sulfonyl group. Clearly, the size of the aromatic sulfonyl groups is quite similar in these IrIII complexes as well as their parent complex IrS-0F. So, they possess alike Tg around 150-160 oC (Table 1). Differently, with increasing the number of the C–F bond, the decomposition temperature ∆T5% of the complexes generally decreases (Table 1), which can be ascribed to the fact that the multiple high-polar C–F bonds can effectively active the complex molecules to make the complexes incline to decompose. However, the ∆T5% over 300 oC should make them suitable for making devices by vacuum deposition method.

(a)

IrS-1F IrS-2F IrS-3F IrS-5F

0.8

0.6

0.4

0.2

0.0

1.0

PL intensity (a.u.)

1.0

Absorption (a.u.)

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


(b)

IrS-1F IrS-2F IrS-3F IrS-5F

0.8

0.6

0.4

0.2

0.0 250

300

350

400

450

500

500

Wavelength (nm)

550

600

650

700

Wavelength (nm)

Figure 2. a) Absorption and b) PL spectra of these IrIII complexes in CH2Cl2 at 293 K.

13


750


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 37

Table 1. Photophysical and thermal data for new IrIII complexes and their fluoro-free parent complex IrS-0F. Compound

Absorption (293 K) λabs (nm) a

IrS-1F

260 (4.70), 280 (4.75), 300 (4.57), 312 (4.41),

Emission λem (nm) 293 K 548, 584

Φp b Solution/Film

τp (µs) c

τr (µs) d

∆T5%/Tg (oC) e

0.96/0.95

1.4

1.5

350/145

554, 590

0.95/0.93

1.1

1.2

315/155

556, 590

0.99/0.98

2.2

2.2

330/165

566, 602

0.97/0.95

1.7

1.8

309/163

547, 580

0.83/0.80

2.4

2.9

375/155

355 (3.81), 390 (3.64), 416(3.57), 476 (3.41) IrS-2F

260 (4.74), 279 (4.79), 300 (4.61), 312 (4.45), 356 (3.85), 392 (3.68), 418 (3.59), 479 (3.43)

IrS-3F

261 (4.72), 280 (4.82), 300 (4.69), 312 (4.51), 360 (3.80), 396 (3.59), 423 (3.49), 486 (3.34)

IrS-5F

261 (4.70), 280 (4.79), 300 (4.63), 314 (4.45), 364 (3.84), 400 (3.69), 427 (3.61), 496 (3,46)

IrS-0F f

261 (4.65), 280 (4.71), 300 (4.61), 354 (3.75),

393 (3.64), 420 (3.57), 475 (3.31) Measured in CH2Cl2 at a concentration of 10−5 M and logε values are shown in parentheses. b In degassed CH2Cl2 relative to fac-[Ir(ppy)3] (Φp = 0.40), λex = 360 nm. c Measured in freeze-pump-thaw degassed CH2Cl2 solutions at a sample concentration of c.a. 10−5 M and the excitation wavelength was set at 355 nm for all the samples at 293 K. d The triplet radiative lifetimes were deduced from τr = τP/Φ P. e ∆T5% is the 5% weight-reduction temperature and Tg is the glass transition temperature. f All the data obtained from the measurements of this turn is very similar to our previous results in ref. 1. a

All of these phosphorescent complexes exhibit two noticeable absorption bands in their UV-Vis spectra (Figure 2a and Table 1). The strong UV absorption bands before 320 nm can be assigned to the spin-allowed S1←S0 transitions of the organic ligands (i.e. 1π–π* bands). The weaker, low-energy features are induced by both 1MLCT←S0 and 3MLCT←S0 (metal-to-ligand charge transfer, MLCT) excitations. The strong spin-orbit coupling effects induced by the heavy metal center are confirmed by the similar oscillator strengths (less than a factor of 2 in their extinction coefficients) for the two MLCT bands (Table 1).27 As indicated by the UV-Vis spectral data (Table 1), the absorption maxima of the MLCT bands show slight bathochromic effect with increasing the number of the fluorine substituents. Furthermore, the bathochromic effect becomes more obvious when more fluorine substituents are introduced to the phenylsulfonyl groups. For example, the bathochromic shift of the 3MLCT absorption band from the fluoro-free parent complex IrS-0F to IrS-1F is ca. 1 nm, while that from IrS-1F to IrS-2F, IrS-2F to IrS-3F and IrS-3F to IrS-5F is ca. 3 nm, 7 nm and 10 nm, respectively 14


Page 15 of 37

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


(Table 1). Under UV light irradiation at 360 nm, all of the complexes emit intense phosphorescence from 548 to 566 nm in CH2Cl2 (Figure 2b and Table 1). Similar to their absorption behaviors, these complexes also exhibit bathochromic effect in their phosphorescence maxima upon introducing more fluorine atoms to the phenylsulfonyl units. Their photoluminescence (PL) spectra have virtually identical line shapes, indicating that similar excited and/or ground states are involved in the phosphorescent transitions. The structureless features associated with the PL spectra indicate their predominantly MLCT character for the lowest triplet excited states (T1) in all of these complexes at 293 K, which have been confirmed by the time-dependent density functional theory (TD-DFT) results (Figure 3 and Table 2). The TD-DFT calculations show that the lowest-energy transitions in these IrIII phosphorescent complexes correspond to the HOMO→LUMO transitions with non-zero oscillator strengths and only the HOMO→LUMO transition is important for the first excited state (Table 2). From the data in Table 2, the molecular orbital (MO) composition represents the characters for both S1 and T1 excited states in these IrIII phosphorescent complexes. Therefore, the HOMO→LUMO transitions can represent the features of the lowest-energy excited state T1, which is the origin of the emission in these complexes. As indicated by the contribution of metal dπ orbitals to the HOMO and LUMO (Table 2), the T1 states involved in these complexes exhibit obvious MLCT characters, which have been corroborated by the structureless line shape of their PL spectra (Figure 2b) and the weak MLCT absorption bands in their UV-Vis spectra (Figure 2a) aforementioned.

15



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 16 of 37

Table 2. Contribution of the metal d porbitals to the HOMO and LUMO together with the TD-DFT calculation results. Contribution of dπ orbitals to LUMOa

IrS-1F

Contributio n of dπ orbitals to HOMOa 46.10%

IrS-2F

46.48%

2.98%

IrS-3F

46.63%

2.68%

IrS-5F

46.84%

2.38%

Compound

a

3.02%

Largest coefficient in the CI expansion of theT1 stateb H→L (0.66112) 510.67 nm H→L (0.66744) 513.62nm H→L (0.66408) 513.83nm H→L (0.66318) 517.24nm

Percentage contribution of H→L transition to the T1 stateb 87.40% 89.10% 88.20% 88.00%

Largest coefficient in the CI expansion of the S1 stateb H→L (0.68215) 458.01nm H→L (0.68284) 460.55nm H→L (0.68580) 460.47nm H→L (0.68534) 462.01nm

Percentage contribution of H→L transition to the S1 stateb 93.10%

Oscillator strength (f) of the S1←S0 transition 0.0384

93.30%

0.0365

94.10%

0.0378

93.90%

0.0365

b

The data have obtained by exporting DFT results with the software AOMix. H → L represents the HOMO to LUMO transition. CI stands for configuration interaction.

Figure 3. The HOMO (up) and LUMO (down) patterns for the IrIII complexes. (a) IrS-1F (b) IrS-2F (c) IrS-3F (d) IrS-5F

Similar to the MO pattern of our previous fluorine-free analogue IrS-0F,1 the pendant fluorophenyl moieties can give noticeable contribution to the LUMO of the IrIII complexes (Figure 3). It means that the electrons in the MLCT processes of these complexes can be hosted by the fluorophenyl moieties besides the pyridyl ring in the organic ligands (Figure 3). Clearly, increasing the number of the fluorine substituents on the pendant fluorophenyl moieties will enhance their electron-accepting ability, which has been indicated by the increased contribution (ca. 5.8% for IrS-1F, 5.9% for IrS-2F, 9.4% for IrS-3F and 13.9% for IrS-5F) from the pendant fluorophenyl units to the LUMOs of the IrIII complexes from IrS-1F to IrS-5F. Hence, the enhanced electron-accepting ability will definitely facilitate the MLCT process from the 16


Page 17 of 37

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


metal center to the pendant fluorophenyl moieties and stabilize the MLCT states accordingly. As a result, the MLCT absorption bands show bathochromic effect from IrS-1F to IrS-5F (Figure 2a and Table 1). Owing to the fact that the phosphorescent emission in these IrIII complexes comes from the 3MLCT states, the bathochromic effect has also been observed in their PL spectra (Figure 2b and Table 1). Owing to the fact that one fluorine group cannot effectively enhance the electron-accepting ability of the pendant phenyl moiety, IrS-1F shows nearly the same maximum phosphorescent wavelength to the fluoro-free parent complex IrS-0F (Table 1). The phosphorescent quantum yields (ΦP) of these IrIII complexes have been measured with fac-[Ir(ppy)3] (ΦP = 0.4) as the standard in degassed CH2Cl2 (Table 2). All these phosphorescent complexes exhibit exceptionally high ΦP > 0.9, which are noticeably higher than that of the fluoro-free parent complex IrS-0F (ΦP ca. 0.83, very close to the reported value ca. 0.86 1). Furthermore, all these IrIII complexes can show very high ΦP in the doped solid film as well (Table 1). All these results indicate that fluorination of the pendant phenyl moiety can exert sound influence on the PL properties of these complexes by enhancing their phosphorescent efficiency, which will definitely benefit their EL performances.

Electrochemical Properties. The electrochemical properties of these IrIII complexes were characterized by cyclic voltammetry (CV) calibrated with ferrocene/ferrocenium (Fc/Fc+) redox couple as an internal reference under a nitrogen atmosphere. The results are presented in Table 3 and Figure 4. All the complexes show one reversible anodic potential Ea (ca. 0.8 V) which can be assigned to the oxidation of the IrIII center. Compared with that of the parent complex IrS-0F at ca. 0.7 V,1 the Ea for these complexes are located in slightly more positive potential region. This can be ascribed to the fact that the fluorophenyl sulfonyl moieties can accept the electron 17



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 18 of 37

from the metal center as aforementioned. Hence, they can reduce the electron density on the IrIII center, which will definitely restrain its oxidation. As a result, the Ea of these complexes move to a more positive potential region. Along this line, the complexes bearing phenylsulfonyl moieties with more fluorine groups should show more positive Ea, which has been confirmed by the data in Table 3 (0.77 V for IrS-1F and IrS-2F vs. 0.78 V for IrS-3F and 0.80 V for IrS-5F). IrS-1F IrS-2F IrS-3F IrS-5F

10 µA

-3

-2

-1

0

1

Potential (V) vs. Ag/AgCl Figure 4. Cyclic voltammograms for the IrIII complexes.

Table 3. Redox properties of the phosphorescent IrIII complexes. Compound Ea (V) Ec (V) Eg (eV) Egopt c / Egcv d 0.77 a -2.07 a, -2.28 b, -2.56 b, -2.81 b 2.37 / 2.71 IrS-1F IrS-2F

0.77 a

-2.06 a, -2.27 b, -2.52 b, -2.77 b

2.36 / 2.70

EHOMO (eV)e -5.57

ELUMO (eV) f -2.86

-5.57

-2.87

-1.98 a, -2.21b, -2.57 b, -2.66 b, 2.35 / 2.63 -5.58 -2.95 -2.87 b 0.80 a -1.85 b, -1.97 b, -2.27 b, -2.30 b, 2.33 / 2.54 -5.60 -3.06 IrS-5F b b -2.57 , -2.75 a Reversible. The value was set as E1/2. b Irreversible or quasi-reversible. The value was derived from the cathodic peak potential. c Optical energy gap Egopt calculated from the absorption onset of cv the UV-vis absorption spectra. d CV energy gap Eg = LUMO – HOMO. e HOMO levels are calculated IrS-3F

0.78 a

according to the equation HOMO = – (4.8 + Ea). f LUMO are obtained from the onset potential of the first reduction wave from the CV data.

18


Page 19 of 37

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


In the cathodic scan, all the complexes exhibit multi reduction processes (Figure 4 and Table 3). With respect to that of the fluoro-free analogue IrS-0F,1 the first reversible process with the cathodic potential (Ec) at ca. -2.10 V for IrS-1F (ca. -2.07 V) and IrS-2F (ca. -2.06 V) can be assigned

to

the

reduction

of

the

sulfonyl

moiety.

The

other

reversible

and

irreversible/quasi-reversible (ill-defined) reduction processes with Ec below -2.20 V should be induced by the reduction of the pyridyl moiety in the organic ligands (Figure 4 and Table 3).28 For IrS-3F, it can be seen clearly that there should be a reversible cathodic peak with Ec ca. -1.98 V, showing a large degree of overlapping with the irreversible one with Ec of ca. -2.21 V (Figure 4). With respect to that of IrS-1F and IrS-2F, the reversible cathodic peak with Ec at ca. -1.98 V should be induced by the sulfonyl moiety as well. Different from IrS-1F and IrS-2F, IrS-3F can show a large irreversible cathodic peak with Ec ca. -2.21 V. Similarly, IrS-5F also exhibits large irreversible cathodic peaks with Ec at ca. -1.85 V and -1.97 V, respectively (Figure 4 and Table 3). The irreversible character for the cathodic peak with Ec of ca. -1.97 V in IrS-5F should exclude its origin from the sulfonyl moiety based on the CV behavior of other analogues. It seems that the cathodic peak for the sulfonyl moiety in IrS-5F should be totally covered by the two large cathodic peaks. Hence, these irreversible cathodic peaks for IrS-3F and IrS-5F should come from the fluorophenyl moiety due to the fact that more fluorine substituents with strong electron-withdrawing ability will make the fluorophenyl moiety much easier to be reduced. This conclusion has been supported by the less negative potential for the first irreversible cathodic peak with Ec at ca. -1.85 V for IrS-5F as compared to that of IrS-3F (ca. -2.21 V) (Figure 4 and Table 3). The absence of these large irreversible cathodic peaks in IrS-1F and IrS-2F indicates that one or two fluorine substituents cannot guarantee the reduction of the fluorophenyl moiety. So, it can be concluded that only introducing three or more fluorine 19



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

substituents to the fluorophenyl moiety can effectively influence the CV behaviors of these complexes. Compared with the first reduction potential of the parent complex IrS-0F (ca. -2.26 V),1 all the fluorinated analogues exhibit obviously less negative first reduction potential (Table 3). Generally, the reduction processes of a molecule refer to the injection of electrons into it. The less negative first reduction potentials associated with these IrIII phosphorescent complexes indicate that fluorination of the phenyl sulfonyl unit can facilitate the EI process effectively. Taking both the oxidation and reduction potentials into consideration, it seems that fluorination of the phenyl sulfonyl unit can make much stronger impact on the reduction processes with respect to the redox behavior of the parent complex IrS-0F due to the direct bounding the fluorine groups to the phenyl sulfonyl units which are responsible for the first reduction process of these complexes. In addition, the LUMO level decreases from IrS-1F to IrS-5F with increasing the number of the fluorine groups (Table 3). Hence, the effect of the number of fluorine groups on the EI ability of these IrIII phosphorescent complexes can be seen clearly as well. Thus, all the fluorinated complexes possess much improved EI capability compared with their parent complex IrS-0F, especially for IrS-3F and IrS-5F. Obviously, these CV results should provide very important information for improving the EI properties of these phosphorescent emitters. As the LUMO level decreases and HOMO level remains nearly unchanged from IrS-1F to IrS-5F, the energy gap (Eg) should decrease from IrS-1F to IrS-5F. This trend has been shown by the Eg values from the LUMO and HOMO levels (i.e. Egcv) obtained from the CV data (Table 3). Clearly, the Egcv data correlate well with the values calculated from the UV-vis absorption onsets (i.e. Egopt). However, the Egcv is slightly larger than Egopt for these IrIII phosphorescent complexes, which might be ascribed the overpotential on the surface of the working electrode in 20


Page 20 of 37

Page 21 of 37

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


the CV measurement.

Electrophosphorescent OLEDs. In order to evaluate the EL properties of these phosphorescent IrIII complexes, OLEDs have been constructed using them as dopants by vacuum deposition approach. In these OLEDs, the well-known CBP was employed as the host material for the phosphorescent emitters. With the aim to show the quality of the doped films, the atomic force microscopy (AFM) images for the surface of the 8 wt % doped CBP films with the concerned phosphorescent emitters have been obtained (Figure 5). It seems that all the doped CBP films possess high quality by showing smooth surfaces with low root mean square roughness (RMS) of ca. 2.0 nm, which is quite desirable for furnishing high-performance devices.

Figure 5. The AFM images for the surface of the 8 wt % doped CBP with different IrIII phosphorescent emitters. (a) IrS-1F, RMS: 2.0 nm (b) IrS-2F, RMS: 2.3 nm (c) IrS-3F, RMS: 2.1 (d) IrS-5F, RMS: 2.4 nm

21



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 22 of 37

The devices based on these IrIII phosphorescent emitters possess the configuration of ITO/MoO3 (3 nm)/CBP (35 nm) CBP:iridium complex (x wt %, 20 nm)/TPBi (65 nm)/LiF (1 nm)/Al (100 nm) (Figure 6). In this device configuration, the hole transporting layer (HTL) and doped emission layer (EML) are formed through regional doping the IrIII complex in CBP with a thickness of 55 nm. The undoped CBP region (ca. 35 nm thick) can play the role of hole transporting, while the doped region (ca. 20 nm thick) serves as EML (Figure 6). Clearly, this strategy will not only simplify the device fabrication, but also reduce structural heterogeneity of the device to facilitate charge injection and transport from the HTL to EML.29,30 In these OLEDs, TPBi serves the function of electron-transporting and hole-blocking because of its relatively low HOMO level. With the aim to optimize their EL performances, these phosphorescent emitters have been doped in the electrophosphorescent OLEDs with different doping levels (Figure 6). Table 4 summarizes the important EL performance data for these devices.

Al (100 nm) LiF (1 nm)

N

TPBi (65 nm) x% Ir dopant:CBP (20 nm)

N CBP

CBP (35 nm) MoO3 (3 nm) ITO Glass

Dopant N

N

N

Devices and doping level

IrS-1F

A1 (6 wt %), A2 (8 wt %), A3 (10 wt %)

IrS-2F

B1 (6 wt %), B2 (8 wt %), B3 (10 wt %)

IrS-3F

C1 (6 wt %), C2 (8 wt %), C3 (10 wt %)

IrS-5F

D1 (6 wt %), D2 (8 wt %), D3 (10 wt %)

N

N

N

TPBi

Figure 6. The configuration of the OLEDs made from these phosphorescent IrIII complexes with fluorophenyl moieties and the chemical structures for the functional materials involved. 22


Page 23 of 37

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


Table 4. The EL performance of the electrophosphorescent OLEDs. Device

Dopant

Vturn-on

Luminance Lmax −2 a

ηext

ηL

ηp

λmax

(V)

(cd m )

(%)

(cd A )

(lm W )

(nm) d

13.9 (3.4) a 13.5 b 12.1 c 15.1 (3.4) 14.2 12.4 12.4 (4.0) 12.3 11.9 11.1 (5.9) 11.0 9.7 13.4 (3.8) 12.4 10.9 11.5 (6.1) 11.3 11.1 14.7 (5.1) 13.8 10.7 19.3 (4.2) 16.4 12.5 14.3 (5.1) 12.9 10.2 9.2 (7.1) 9.1 7.2 10.7 (6.5) 10.1 8.2 9.6 (6.3) 9.3 8.2 13.7 (3.8) 13.5 11.9

60.1 (3.4) 58.8 52.6 65.2 (3.4) 60.9 54.5 53.9 (4.0) 53.3 51.8 46.7 (5.9) 46.4 40.9 56.6 (3.8) 51.7 46.2 48.3 (6.1) 47.3 46.4 62.1 (5.1) 57.9 44.8 81.2 (4.2) 67.2 51.7 60.1 (5.1) 54.7 43.9 36.6 (7.1) 35.9 28.4 42.5 (6.5) 40.5 32.5 38.1 (6.3) 36.7 31.7 45.7 (3.8) 44.8 39.7

60.6 (3.0) 46.4 35.6 65.9 (3.0) 50.3 37.2 43.6 (3.8) 43.5 36.7 25.5 (5.7) 25.0 19.4 53.2 (3.2) 29.2 22.2 27.2 (5.1) 26.9 22.4 39.1 (4.8) 31.1 20.5 64.5 (3.8) 36.0 24.1 39.5 (4.6) 30.0 19.8 16.5 (6.9) 15.6 11.3 21.4 (6.1) 17.9 12.9 20.6 (5.5) 16.5 12.8 41.9 (3.4) 29.3 16.9

544 (0.42, 0.56)

A1

IrS-1F (6.0 wt %)

3.0

35696 (10.9)

A2

IrS-1F (8.0 wt %)

3.1

36056 (10.9)

A3

IrS-1F (10.0 wt %)

3.2

37064 (10.7)

B1

IrS-2F (6.0 wt %)

4.3

29258 (11.5)

B2

IrS-2F (8.0 wt %)

3.6

34062 (10.9)

B3

IrS-2F (10.0 wt %)

3.6

33720 (11.9)

C1

IrS-3F (6.0 wt %)

4.0

31755 (11.9)

C2

IrS-3F (8.0 wt %)

3.8

28464 (11.5)

C3

IrS-3F (10.0 wt %)

3.9

30939 (12.3)

D1

IrS-5F (6.0 wt %)

5.3

13370 (12.3)

D2

IrS-5F (8.0 wt %)

5.1

13446 (12.3)

D3

IrS-5F (10.0 wt %)

4.8

13032 (11.9)

F

IrS-0F (8.0 wt %)

3.4

30467 (15.0)

−1

a

−1

544 (0.42, 0.56) 544 (0.42, 0.56) 548 (0.44, 0.55) 548 (0.44, 0.55) 548 (0.44, 0.55) 552 (0.44, 0.55) 552 (0.44, 0.55) 552 (0.44, 0.55) 556 (0.46, 0.52) 556 (0.46, 0.52) 556 (0.46, 0.52) 544 (0.43, 0.53)

Maximum values of the devices. Values in parentheses are the voltages at which they were obtained. b Values were collected at 100 cd m−2. c Values collected at 1000 cd m−2. d Values were collected at 8 V and CIE coordinates (x, y) are shown in parentheses.

23



1.0

EL intensity (a.u.)

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

Device Device Device Device

0.8

Page 24 of 37

A2 B2 C2 D2

0.6

0.4

0.2

0.0 450

500

550

600

650

700

Wavelength (nm)

Figure 7. The EL spectra for the optimized OLEDs at ca. 8V.

After applying a proper voltage, these OLEDs exhibited intense yellow electroluminescence. As depicted in Figure 7, the EL spectral profile of each optimized device is identical to the PL spectrum of the corresponding IrIII complex, suggesting that the EL emission indeed originates from the triplet excited states of the IrIII phosphors. Additionally, no residual emission from CBP is observed in these devices, implying the efficient forward energy transfer from the host excitons to the phosphorescent molecules and effective confinement of the excitons on the IrIII phosphors to guarantee the high EL efficiencies. The current density–voltage–luminance (J−V−L) characteristics and EL efficiency–luminance curves for the OLEDs are shown in Figure 8, Figure 9 and SI (Figure S2 and Figure S3). All the devices show the turn-on voltages in the range from 3.0 V to 5.3 V (Table 4). Owing to the high ΦP and EI/ET ability associated with these IrIII phosphors, all our phosphorescent OLEDs can show exceptional EL performances. For all the phosphoescent emitters, their maximum EL ability has been achieved at the doping level of ca. 8 wt %. The optimized device (Device C2) doped with IrS-3F can exhibit the best EL performance with a turn-on voltage (Vturn-on) of 3.8 V, and a maximum luminance (Lmax) of 28464 cd m−2 at 11.5 V, a peak luminance efficiency (ηL) of 24


Page 25 of 37

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


81.2 cd A−1, corresponding to a peak power efficiency (ηP) of 64.5 lm W−1 and a peak external quantum efficiency (ηext) of 19.3% (Table 4). Obviously, the peak ηL of 81.2 cd A−1 for device C2 will definitely set IrS-3F among the state-of-the-art highly efficient yellow phosphors. In addition, the device A2 with IrS-1F as emitter can also exhibit remarkable EL performances with Lmax of 36056 cd m−2 at 10.9 V, ηL of 65.2 cd A−1, ηP of 65.9 lm W−1 and ηext of 15.1% (Table 4). Despite their lower EL efficiencies with respect to those of devices A2 and C2, devices B2 and D2 still can show attractive EL data. The peak EL efficiencies for device B2 are 56.6 cd A−1, 53.2 lm W−1 and 13.4%, while 42.5 cd A−1, 21.4 lm W−1 and 10.7% have been achieved in device D2 (Table 4). Compared with the maximum EL efficiencies of 45.7 cd A−1, 41.9 lm W−1 and 13.7% achieved by the fluoro-free parent complex IrS-0F by the same device configuration (Table 4 and Figure S4), the optimized devices A2, B2 and C2 can furnish substantially improved EL performances. Hence, it can be seen clearly that introducing fluorine substituents to the pendant phenyl moiety should represent very convenient and effective strategy for enhancing the EL abilities of the IrIII phosphors functionalized with the sulfonyl unit. The fluorine substituents attached to aromatic units can show both inductive and resonance effects. Owing to the much stronger electronegativity of fluorine than carbon, the inductive effect of fluorine substituents exhibits strong electron-withdrawing features which will enhance the EI/ET capability. However, the resonance effect induced by the fluorine substituents will donate electron to the aromatic units attached, which will benefit the HI/HT ability. Based on the mechanism of the EL process, all these features will definitely benefit the EL performances of the concerned emitters. Hence, these fluorinated IrIII phosphors can show very high EL efficiencies as aformentioned. However, it is well known that the electron-withdrawing inductive effect of the fluorine substituents is 25



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

much stronger than their electron-donating resonance effect. Hence, the enhanced the EL properties for these IrIII phosphors should be mainly ascribed to their improved EI/ET ability afforded by the sulfonyl unit with fluorophenyl group. In order to support this conclusion, the hole- and electron-only devices have been fabricated for these IrIII phosphors and their mother complexes. From the current density–voltage (J−V) curves for the hole-only devices (Figure S5a), the introduction of fluorine substituents can only have minor effect on the HI/HT abilities of these IrIII phosphors for their quite similar current density under the same driving voltage. However, the fluorine substituents can effectively enhance the EI/ET properties of these IrIII phosphors, since all the IrIII phosphors can show noticeably higher current density under the same driving voltage in their electron-only devices with respect to that of their fluoro-free mother complex IrS-0F. (Figure S5b). Typically, the organic semiconductors possess much higher HT ability as compared with their ET property,19 which should induce their unbalanced injection/transporting ability for holes and electrons. Clearly, the enhanced EI/ET properties of these IrIII phosphors will benefit their more balanced charge carrier injection/transporting behavior. So, these IrIII phosphors can show much better EL efficiencies with respect to those of their fluoro-free mother complex as aforementioned. In addition, the high ΦP shoud also be a key factor to furnish high EL efficiencies to these IrIII phosphors.31 From all the results aformentioned, fluorination can definitely play a critical role in improving the EL performances of the IrIII phosphors with aromatic sulfonyl group through optimizing both the charge carrier injection/transporting behaviors and ΦP. According to their molecular orbital energy levels, these IrIII phosphors share very similar HOMO levels (Table 3). So, the effect from the molecular orbital energy levels of these IrIII phosphors on their EL performances should mainly come from the HUMO levels. From the CV 26


Page 26 of 37

Page 27 of 37

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


results aformentioned (Figure 4 and Table 3), IrS-3F possesses lower LUMO level and hence shows better EI ability as compared with both IrS-1F and IrS-2F. Among all these IrIII phosphors, IrS-3F should also possess the best ET ability in view of its highest current density in the electron-only devices (Figure S5b). It means that IrS-3F can exhibit higher EI/ET ability than IrS-1F and IrS-2F to maintain its more balanced charge carrier injection/transporting capacity. So, it should be reasonable that the optimized device doped with IrS-3F can furnish higher EL efficiencies than those made from IrS-1F and IrS-2F (Table 4). Considering both the chemical structure and CV results (Figure 4 and Table 3), IrS-5F should outperform IrS-3F in OLEDs due the fact that IrS-5F exhibits even lower LUMO level than IrS-3F (Table 3) to furnish IrS-5F with even enhanced capacity of achieving balanced charge carrier injection/transporting and hence higher EL efficiencies. However, the devices with IrS-5F as emitter cannot provide the expected EL efficiencies (Table 4) and the current density in its electron-only device is also lower than that of IrS-3F (Figure S5b). This might be caused by the decomposition of IrS-5F in the process of the device fabrication due to its lower ∆T5% of 309 oC (Table 1) induced by the multiple C-F bonds.32 Obviously, the impurity produced in the decomposition process should seriously hamper the EL performance of IrS-5F. Also, the slightly inferior EL performance of IrS-2F with respect to that of IrS-1F might be assigned to the same reason due its relatively lower ∆T5% (ca. 315 oC). Hence, these results should provide very important information for optimizing the EL performances of the fluoro-containing phosphorescent emitters. There are highly efficient yellow phosphorescent emitters reported,33-35 including the ones with dibenzothiophene-S,S-dioxide-2-yl unit (58.4 cd A

−1 35

).

Our recently

reported asymmetric phosphors with the fluoro-free sulfonyl moiety can achieve high EL efficiency of 69.4 cd A−1.17,18 In view of the attractive EL performances achieved by these 27



documented yellow phosphors, the exceptional EL efficiencies associated with these functionalized triplet emitters (ηL of 81.2 cd A−1, ηP of 64.5 lm W−1 and ηext of 19.3%) will definitely show their great potential in OLEDs. To the best of our knowledge, these phosphores have furnished the highest EL efficiencies for the phosphorescent complexes bearing the functional sulfonyl groups. Device A2 Device B2 Device C2 Device D2

400

10000

1000 300 100 200 10

)

-2

100

Luminance (cd m

Current density ( mA cm-2)

500

2

4

6

8

10

12

1

Voltage (V)

Figure 8. The current density–voltage–luminance (J−V−L) curves for the optimized OLEDs.

100

100

Device A2

Device B2 10

ηex t

1

10

η ext

100

1000

1

ηP

Luminance ( cd m

1

10000

)

1

ηL

L

ηP

1

10

P

η /η

P

ηL

L

η /η

1

( cd A- 1/ lm W- 1)

10

10

100

1000

Luminance ( cd m

-2

-2

28


)

10000

η (%) ext

(cd A- 1/ lm W- 1)

10

ηext (%)

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 28 of 37

Page 29 of 37

100 Device C2

100

Device D2 10

1

ηex t

10

ηex t

1

ηL

P

0.1

ηP 1

1

100

1000

Luminance ( cd m

0.1

10000

)

0.1

ηP

L

1

10

η /η

L

η /η

P

ηL

(cd A- 1/ lm W- 1)

10

10

100

1000

Luminance ( cd m

-2

ηext (%)

(cd A- 1/ lm W- 1)

10

ηext (%)

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


10000

)

-2

Figure 9. The relationship between the EL efficiency and luminance for the optimized OLEDs.

CONCLUSION In conclusion, new functional IrIII phosphors with fluorinated sulfonyl units have been successfully developed. Critically, these phosphorescent emitters not only show exceptionally high ΦP (> 0.9) at room temperature, but also furnish outstanding EL performances with maximum luminance efficiency (ηL) of 81.2 cd A−1, corresponding to power efficiency (ηP) of 64.5 lm W−1 and external quantum efficiency (ηext) of 19.3% with the CIE coordinates of (0.44, 0.55). All these encouraging data will certainly guarantee the great potential of these phosphorescent emitters with improved EI/ET abilities in the field of electroluminescence. Furthermore, this investigation will provide very important information about the critical role played by the fluorinated sulfonyl moieties in tuning the optoelectronic behaviors of these phosphorescent emitters. Hence, the obtained results should afford valuable clues for developing highly efficient triplet emitters with great potential for practical application.

ASSOCIATED CONTENT Supporting Information Synthesis of intermediates and ligands, Some single crystal data and EL data. 29



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

This material is available free of charge via the Internet at http://pubs.acs.org. Author Contributions J.Z. prepared all the complexes and characterized the basic photophysical properties. X.L.Y, X.G.Y. and H.M.Z. prepared some intermediate compounds. X.B.X measured the CV curves. Y.Y. and Z.X.W. designed the structure of the OLEDs and Y.Y. fabricated the devices. Y.X.R. and W.Y.W. participated in X-ray crystallographic analysis. G.J.Z. designed the complexes supervised the overall project. G.J.Z. also contributed to analysis and writing of the whole paper.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. (G.Z.) *E-mail: [email protected]. (Z.W.) *E-mail: [email protected]. (Y.R.) *E-mail: [email protected]. (W.W.) Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS This work was financially supported by Tengfei Project from Xi’an Jiaotong University, the Fundamental Research Funds for the Central Universities (cxtd2015003), The Program for New Century Excellent Talents in University, the Ministry of Education of China (NECT-09-0651), the Key Creative Scientific Research Team in Shaanxi Province (2013KCT-05), the China Postdoctoral Science Foundation (Grant No. 20130201110034), and the National Natural Science Foundation of China (No. 20902072, 21572716). W.-Y.W. acknowledges the financial 30


Page 30 of 37

Page 31 of 37

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


support from the National Basic Research Program of China (973 Program, grant no. 2013CB834702), the Science, Technology and Innovation Committee of Shenzhen Municipality (JCYJ20140419130507116), the Areas of Excellence Scheme, University Grants Committee of HKSAR, China (no. AoE/P-03/08), Hong Kong Research Grants Council (no. HKBU 203313) and Hong Kong Baptist University (no. FRG1/14-15/084).

REFERENCES (1) Zhou, G.; Ho, C.-L.; Wong, W.-Y.; Wang, Q. Ma, D.; Wang, L.; Lin, Z.; Marder, T. B.; Beeby,

A.

Manipulating

Charge-Transfer

Character

with

Electron-Withdrawing

Main-Group Moieties for the Color Tuning of Iridium Electrophosphors. Adv. Funct. Mater. 2008, 18, 499-511. (2) Sasabe, H.; Seino, Y.; Kimura, M.; Kido, J. A m-terphenyl-modifed Sulfone Verivative as a Host Material for High-Efficiency Blue and Green Phosphorescent OLEDs. Chem. Mater. 2012, 24, 1404-1406. (3) Kim, S. J.; Leroy, J.; Zuniga, C.; Zhang, Y. D.; Zhu, L. Y.; Sears, J. S.; Barlow, S.; Bredas, J. L.; Marder, S. R.; Kippelen, B. High-Efficiency Blue-Green Electrophosphorescent Light-Emitting Devices Using a Bis-Sulfone as Host in the Emitting Layer. Org. Electron. 2011, 12, 1314-1318. (4) Ban, X. X.; Xu, H. G.; Yuan, G. L.; Jiang, W.; Huang, B.; Sun, Y. M. Spirobifluorene/Sulfone Hybrid: Highly Efficient Solution-Processable Material for UV-Violet Electrofluorescence, Blue and Green Phosphorescent OLEDs. Org. Electron. 2014, 15, 1678-1686. (5) Hsu, F. M.; Chien, C. H.; Hsieh, Y. J.; Wu, C. H.; Shu, C. F.; Liu, S. W.; Chen, C. T. Highly 31



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

Efficient

Red

Electrophosphorescent

Device

Incorporating

Page 32 of 37

a

Bipolar

Triphenylamine/Bisphenylsulfonyl-Substituted Fluorene Hybrid as the Host. J. Mater. Chem. 2009, 19, 8002-8008. (6) Zhou, G.; Yang, X.; Wong, W.-Y.; Wang, Q.; Suo, S.; Ma, D. Feng, J.; Wang, L. A Robust Yellow-Emitting Metallophosphor with Electron-Injection/-Transporting Traits for Highly Efficient White Organic Light-Emitting Diodes. ChemPhysChem 2011, 12, 2836-2843. (7) Ma, Y. G.; Zhang, H. Y.; Shen, J. C.; Che, C. M. Electroluminescence from Triplet Metal-Ligand Charge-Transfer Excited State of Transition Metal Complexes. Synth. Met. 1998, 94, 245-248. (8) Baldo, M. A.; O'Brien, D. F.; You, Y.; Shoustikov, A.; Sibley, S.; Thompson, M. E.; Forrest, S. R. Highly Efficient Phosphorescent Emission from Organic Electroluminescent Devices. Nature 1998, 395, 151-154. (9) Xiao, L. X.; Chen, Z. J.; Qu, B.; Luo, J. X.; Kong, S.; Gong, Q. H.; Kido, J. J. Recent Progresses on Materials for Electrophosphorescent Organic Light-Emitting Devices. Adv. Mater. 2011, 23, 926-952. (10) Yang, X. L.; Yao, C. L.; Zhou, G. J. Highly Efficient Phosphorescent Materials Based on Platinum Complexes and Their Application in Organic Light-Emitting Devices (OLEDs). Platinum Met. Rev. 2013, 57, 2-16. (11) You, Y.; Park, S. Y.

Phosphorescent Iridium (III) Complexes: Toward High

Phosphorescence Quantum Efficiency Through Ligand Control. Dalton Trans. 2009, 1267-1282. (12) Chou, P. T.; Chi, Y. Phosphorescent Dyes for Organic Light-Emitting Diodes. Chem. Eur. J. 2007, 13, 380-395. 32


Page 33 of 37

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


(13) Tao, Y. T.; Yang, C. L.; Qin, J. G. Organic Host Materials for Phosphorescent Organic Light-Emitting Diodes. Chem. Soc. Rev. 2011, 40, 2943-2970. (14) Zhou, G. J.; Wang, Q.; Ho, C. L.; Wong, W. Y.; Ma, D. G; Wang, L. X.; Lin, Z. Y. Robust Tris-cyclometalated Iridium (III) Phosphors with Ligands for Effective Charge Carrier Injection/Transport: Synthesis, Redox, Photophysical, and Electrophosphorescent Behavior. Chem. Asian J. 2008, 3, 1830-1841. (15) Zhou, G. J.; Wang, Q.; Wang, X. Z.; Ho, C. L.; Wong, W. Y.; Ma, D. G.; Wang, L. X.; Lin, Z. Y. Metallophosphors of Platinum with Distinct Main-Group Elements: a Versatile Approach Towards Color Tuning and White-Light Emission with Superior Efficiency/Color Quality/Brightness Trade-Offs. J. Mater. Chem. 2010, 20, 7472-7484. (16) Yang, X.; Xu, X.; Zhao, J.; Dang, J.-S.; Huang, Z.; Yan, X.; Zhou, G.; Wang, D. Phosphorescent Platinum (II) Complexes Bearing 2-Vinylpyridine-type Ligands: Synthesis, Electrochemical and Photophysical Properties, and Tuning of Electrophosphorescent Behavior by Main-Group Moieties. Inorg. Chem. 2014, 53, 12986-13000. (17) Xu, X. B.; Yang, X. L.; Dang, J. S.; Zhou, G. J.; Wu, Y.; Li, H.; Wong, W. Y. Trifunctional IrIII ppy-Type Asymmetric Phosphorescent Emitters with Ambipolar Features for Highly Efficient Electroluminescent Devices. Chem. Commun. 2014, 50, 2473-2476. (18) Xu, X. B.; Yang, X. L.; Wu, Y.; Zhou, G. J.; Wu, C.; Wong, W. Y. Heteroleptic Cyclometalated Iridium (III) Complexes with Ambipolar or Electron Injection/Transport Features for Highly Efficient Electrophosphorescent Devices. Chem. Asian J. 2015, 10, 252-262. (19) Antoniadis, H.; Abkowitz, M. A.; Hsieh, B. R. Carrier Deep-Trapping Mobility-Lifetime Products in Poly(p-Phenylene Vinylene). Appl. Phys. Lett. 1994, 65, 2030-2032. 33



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

(20) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure Refinement; University of Göttingen: Göttingen, Germany, 1997. (21) Sheldrick, G. M. SADABS; University of Göttingen: Göttingen, Germany, 1996. (22) Wadt, W. R.; Hay, P. J. Ab Initio Effective Core Potentials for Molecular Calculations. Potentials for Main Group Elements Na to Bi. J. Chem. Phys. 1985, 82, 284-298. (23) Hay, P. J.; Wadt, W. R. Ab Initio Effective Core Potentials for Molecular Calculations. Potentials for K to Au Including the Outermost Core Orbitals. J. Chem. Phys. 1985, 82, 299-310. (24) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, Revision A.01; Gaussian, Inc.: Wallingford, CT, 2009. (25) Brooks, J.; Babayan, Y.; Lamansky, S.; Djurovich, P. I.; Tsyba, I.; Bau, R.; Thompson, M. E. Synthesis and Characterization of Phosphorescent Cyclometalated Platinum Complexes. 34


Page 34 of 37

Page 35 of 37

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


Inorg. Chem. 2002, 41, 3055-3066. (26) Yang, C.; Zhang, X.; You, H.; Zhu, L.; Chen, L.; Zhu, L.; Tao, Y.; Ma, D.; Shuai, Z.; Qin, J. Tuning the Energy Level and Photophysical and Electroluminescent Properties of Heavy Metal Complexes by Controlling the Ligation of the Metal with the Carbon of the Carbazole Unit. Adv. Funct. Mater. 2007, 17, 651-661. (27) Lamansky, S.; Djurovich, P.; Murphy, D.; Abdel-Razzaq, F.; Lee, H.-E.; Adachi, C.; Burrows, P. E.; Forrest, S. R.; Thompson, M. E. Highly Phosphorescent Bis-cyclometalated Iridium Complexes: Synthesis, Photophysical Characterization, and Use in Organic Light Emitting Diodes. J. Am. Chem. Soc. 2001, 123, 4304-4312. (28) Yang, X.; Sun, N.; Dang, J.; Huang, Z.; Yao, C.; Xu, X.; Ho, C.-L.; Zhou, G.; Ma, D.; Zhao, X.; Wong, W.-Y. Versatile Phosphorescent Color Tuning of Highly Efficient Borylated Iridium (III) Cyclometalates by Manipulating the Electron-Accepting Capacity of the Dimesitylboron Group. J. Mater. Chem. C 2013, 1, 3317-3326. (29) Wang, Z. B.; Helander, M. G.; Qiu, J.; Puzzo, D. P.; Greiner, M. T.; Liu, Z. W.; Lu, Z. H. Highly Simplified Phosphorescent Organic Light Emitting Diode with >20% External Quantum Efficiency at > 10,000 cd/m2. Appl. Phys. Lett. 2011, 98, 073310. (30) Liehm, P.; Murawski, C.; Furno, M.; Lüssem, B.; Leo, K.; Gather, M. C. Comparing the Emissive Dipole Orientation of Two Similar Phosphorescent Green Emitter Molecules in Highly Efficient Organic Light-Emitting Diodes. Appl. Phys. Lett. 2012, 101, 253304. (31) Tsutsui, T. Progress in Electroluminescent Devices Using Molecular Thin Films. MRS Bulletin 1997, 39-45. (32) Sivasubramaniam, V.; Brodkorb, F.; Hanning, S.; Loebl, H. P.; van Elsbergen, V.; Boerner, H.; Scherf, U.; Kreyenschmidt, M. Fluorine Cleavage of the Light Blue Heteroleptic Triplet 35



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

Emitter FIrpic. J. Fluorine Chem. 2009, 130, 640-649. (33) Laskar, I. R.; Chen, T. M. Tuning of Wavelengths: Synthesis and Photophysical Studies of Iridium Complexes and Their Applications in Organic Light Emitting Devices. Chem. Mater. 2004, 16, 111-117. (34) Hung, W. Y.; Chi, L. C.; Chen, W. J.; Chen, Y. M.; Chou, S. H.; Wong, K. T. A New Benzimidazole/Carbazole Hybrid Bipolar Material for Highly Efficient Deep-Blue Electrofluorescence, Yellow-Green Electrophosphorescence, and Two-Color-Based White OLEDs. J. Mater. Chem. 2010, 20, 10113-10119. (35) Liu, D.; Ren, H.; Deng, L. Zhang, T. Synthesis and Electrophosphorescence of Iridium Complexes Containing Benzothiazole-Based Ligands. ACS Appl. Mater. Interfaces 2013, 5, 4937-4944.

36


Page 36 of 37

Page 37 of 37

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


For Table of Contents Only

37


Phosphorescent Iridium(III) Complexes Bearing Fluorinated Aromatic

Recommend Documents