Abstract:
Synthesis of platinum(II) di(2-pyrazolyl)benzene chloride and analogs includes forming a 1,3-di-substituted benzene including two aromatic five-membered heterocycles, and reacting the 1,3-di-substituted benzene with an acidic platinum-containing solution to form a luminescent platinum(II) complex. The luminescent platinum(II) complex is capable of emitting blue and white light and can be used as an emitter in a light emitting device.

Description:
PRIORITY CLAIM AND RELATED PATENT APPLICATION 
       [0001]    This document claims priority from U.S. Patent Provisional Application Ser. No. 61/016,155 entitled “Platinum(II) Di(2-Pyrazolyl) Benzene Chloride Analogs and Uses” and filed on Dec. 21, 2007, the entire contents of which are incorporated herein by reference as part of the disclosure of this document. 
     
    
     TECHNICAL FIELD 
       [0002]    This invention relates to platinum(II) di(2-pyrazolyl)benzene chloride and analogs, and more particularly to the synthesis and use thereof. 
       BACKGROUND 
       [0003]    As depicted in  FIG. 1 , an organic light-emitting device (OLED)  100  may include a layer of indium tin oxide (ITO) as an anode  102 , a layer of hole-transporting materials (HTL)  104 , a layer of emissive materials (EML)  106  including emitter(s) and host(s), a layer of electron-transporting materials (ETL)  108 , and a metal cathode layer  110  on substrate  112 . The emission color of OLED  100  may be determined by the emission energy (optical energy gap) of the emitter(s) in the layer of emissive materials. Phosphorescent OLEDs (i.e., OLEDs with phosphorescent emitters) may have higher device efficiency than fluorescent OLEDs (i.e., OLEDs with fluorescent emitters). Some emitters for blue phosphorescent OLEDs include iridium—a relatively scarce element—in the form of cyclometalated iridium complexes. 
       SUMMARY 
       [0004]    In one aspect, a luminescent compound has the generic formula 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    is an aromatic heterocycle
 
and where W is —Cl or
 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    The six-membered ring in this generic formula denotes benzene or pyridine. 
         [0005]    In another aspect, a light emitting device includes the luminescent compound shown above. 
         [0006]    In certain implementations, 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    is selected from the group consisting of 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    In certain implementations, the luminescent compound is platinum(II) di(2-pyrazolyl)benzene chloride, with the formula: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0007]    In some implementations, the luminescent compound is phosphorescent. The compound is capable of emitting light in the blue range of the visible spectrum. In some cases, the compound is capable of emitting white light. The light emitting device may be an organic light emitting device. 
         [0008]    In another aspect, a method of making a platinum(II) complex includes forming a 1,3-di-substituted aromatic six-membered ring with two aromatic five-membered heterocycles, and reacting the 1,3-di-substituted six-membered ring with an acidic platinum-containing solution to form the platinum(II) complex. 
         [0009]    In some implementations, the aromatic five-membered heterocycles are selected from the group consisting of pyrazolyl, substituted pyrazolyl, imidazolyl, substituted imidazolyl, thiazolyl, and substituted thiazolyl. In certain implementations, the benzene is fluorinated, difluorinated, or methylated. Fluorinating the benzene ring may increase the emission energy, shifting the emission toward the blue end of the visible spectrum. The benzene may be bonded to a heteroatom, such as a nitrogen atom or a sulfur atom, in the heterocycle. The platinum atom in the platinum(II) complex may be bonded to a carbon atom and two nitrogen atoms. In some embodiments, the platinum(II) complex is platinum(II) di(2-pyrazolyl)benzene chloride. In certain implementations, the aromatic six-membered ring is benzene or pyridine. In some cases, when the six-membered ring is pyridine, an increase in the emission energy may result. 
         [0010]    Phosphorescent blue OLEDs with the platinum complexes described herein as emitters can be produced at low cost and provide operationally stable displays. 
         [0011]    The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0012]      FIG. 1  illustrates an organic light emitting device (OLED). 
           [0013]      FIG. 2  shows precursors for platinum(II) di(2-pyrazolyl)benzene chloride and analogs. 
           [0014]      FIG. 3  shows platinum(II) di(2-pyrazolyl)benzene and analogs. 
           [0015]      FIG. 4  shows a room temperature emission spectrum of platinum(II) di(2-pyrazolyl)benzene chloride in dichloromethane. 
           [0016]      FIG. 5  shows room temperature and 77K emission spectra of platinum(II) di(3,5-dimethyl-2-pyrazolyl)benzene chloride in solution. 
           [0017]      FIG. 6  shows a room temperature emission spectrum of platinum(II) di(3,5-dimethyl-2-pyrazolyl)benzene chloride in thin film of poly(methyl methacrylate) (PMMA). 
           [0018]      FIG. 7  shows a room temperature emission spectrum of platinum(II) di(3,5-dimethyl-2-pyrazolyl)benzene phenoxide in a thin film of poly(carbonate). 
           [0019]      FIG. 8  shows a room temperature emission spectrum of platinum(II) di(3,5-dimethyl-2-pyrazolyl)toluene chloride in a thin film of poly(methyl methacrylate) (PMMA). 
           [0020]      FIG. 9  shows a room temperature emission spectrum of platinum(II) di(methyl-imidazolyl)benzene chloride in a solution of dichloromethane. 
           [0021]      FIG. 10  shows a room temperature emission spectrum of platinum(II) di(methyl-imidazolyl)benzene chloride in a thin film of poly(methyl methacrylate) (PMMA). 
           [0022]      FIG. 11A  shows a room temperature emission spectrum of platinum(II) di(methyl-imidazolyl)toluene chloride in a thin film of poly(methyl methacrylate) (PMMA). 
           [0023]      FIG. 11B  shows a 77K emission spectrum of platinum(II) di(methyl-imidazolyl)pyridine chloride in a solution of 2-methyl-tetrahydrofuran. 
           [0024]      FIG. 12  shows a room temperature emission spectrum of platinum(II) di(thiazolyl)(4,6-difluoro-benzene) chloride in a solution of dichloromethane. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    The platinum complexes described herein can be used as emitters for OLEDs, absorbers for solar cells, luminescent labels for bio-applications, and the like. Blue phosphorescent OLEDs may include platinum complexes with high band-gap ligands, including the five-membered rings depicted herein. 
         [0026]    Platinum(II) di(2-pyrazolyl)benzene chloride and analogs may be represented as: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    in which: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    is an aromatic heterocycle, 
       and W can be —Cl or 
       [0027]    
       
                 
         
             
             
         
       
     
         [0028]    The aromatic six-membered ring in this generic formula denotes benzene or pyridine. The aromatic five-membered heterocycle can be, for example, substituted pyrazolyl, imidazolyl, substituted imidazolyl, thiazolyl, and substituted thiazolyl ligands shown below: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    In some embodiments, the luminescent compound is platinum(II) di(2-pyrazolyl)benzene chloride, shown below: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    In some cases, the benzene ring is substituted, such as fluorinated or methylated in one or more positions. Fluorinating the benzene ring increases the emission energy, shifting the emission toward the blue end of the visible spectrum. In certain cases, the six-membered ring is a pyridyl ring rather than benzene. 
         [0029]    Platinum(II) di(2-pyrazolyl)benzene chloride and analogs described herein may be prepared from the ligands depicted in  FIG. 2 . Synthesis of the ligands is described below. 
         [0030]    HL 1 : After standard cycles of evacuation and back-fill with dry and pure nitrogen, an oven-dried Schlenk flask equipped with a magnetic stir bar was charged with Cu 2 O (0.1 mmol, 10 mol %), syn-2-pyridinealdoxime (0.4 mmol, 20 mol %), the pyrazole (2.5 mmol), Cs 2 CO 3  (5.0 mmol), and the 1,3-dibromobenzene (1.0 mmol), and anhydrous and degas sed acetonitrile (20 mL). The flask was stirred in an oil bath, and refluxed for 3 days. The reaction mixture was allowed to cool to room temperature, diluted with dichloromethane and filtered through a plug of CELITE® (World Minerals Inc., Santa Barbara, Calif.), the filter cake being further washed with dichloromethane (20 mL). The filtrate was concentrated under vacuo to yield a residue, which was purified by flash column chromatography on silica gel to obtain the pure product HL 1  in80% yield.  1 H NMR (CDCl 3 ): 6.51 (dd, 2H), 7.52 (t, 1H), 7.62 (dd, 2H), 7.76 (d, 2H), 8.02 (d, 2H), 8.10 (s, 1H). 
         [0031]    HL 2 : HL 2  was synthesized in 64% yield using the same procedure as HL 1  except that 1,3-diiodobenzene was used as starting material.  1 H NMR (CDCl 3 ): 2.6 (s 12H), 6.0 (s, 2H), 7.42 (dd, 2H), 7.51 (t, 2H), 7.55 (t, 2H). 
         [0032]    HL 3 : 1,3-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzene (1.0 mmol), Pd(OAc) 2  (0.05 equiv), PPh 3  (0.2 equiv), 1-methyl-2-iodoimidazole (2.5 mmol) were resolved in dimethoxyethane/2M K 2 CO 3  aqueous solution (20 mL, 1:1) under nitrogen atmosphere. The mixture was heated and refluxed for 24 h. After being cooled to room temperature, the reaction mixture was diluted with EtOAc, and poured into a brine solution. The organic layer was separated, and washed with the water, dried, filtered, and the filtrate was concentrated under reduced pressure. The residue was purified by column chromatography on silica gel to obtain the pure product HL 3  in 34% yield.  1 H NMR (CDCl 3 ): 3.72 (s 6H), 7.12 (d, 2H), 7.47 (t, 1H), 7.48 (d, 2H), 7.56 (s, 1H), 7.72 (d, 2H). 
         [0033]    HL 4 : HL 4  was synthesized in 40% yield using the same procedure as HL 3  except that 1,3-difluoro-4,6-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzene was used as starting material instead of 1,3-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-benzene.  1 H NMR (CDCl 3 ): 3.63 (s, 6H), 7.09 (t, 1H), 7.13 (d, 2H), 7.35 (t, 1H), 7.60 (d, 2H). 
         [0034]    HL 5 : HL 5  was synthesized in 25% yield using the same procedure as HL 3  except that 2-bromothiozole was used as starting material instead of 1-methyl-2-iodoimidazole.  1 H NMR (CDCl 3 ): 7.13 (t, 1H), 7.49 (d, 2H), 7.98 (d, 2H), 9.23 (t, 1H). 
         [0035]    HL 6 : HL 6  was synthesized in 65% yield using the same procedure as HL 1  except that imidazole was used as starting material.  1 H NMR (DMSO): 7.26 (2H), 7.34 (2H), 7.41 (1H), 7.43 (2H), 7.62 (1H), 7.92 (2H). 
         [0036]    HL 7 : Methyl iodide (3 equiv) was syringed into a 50 mL round-bottomed flask charged with HL 6  (10 mmol) and DMSO (30 mL). The reaction was stirred under nitrogen in room temperature for 48 h. The mixture was poured into EtOAc (60 mL), and the white precipitate was formed, filtered, washed with ether, and air-dried to obtain HL 7  in 85% yield.  1 H NMR (DMSO): 3.99 (s, 6H), 7.97-8.00 (m, 3H), 8.00 (s, 2H), 8.31 (s, 1H), 8.37 (s, 2H), 9.89 (s, 2H). 
         [0037]    HL 8 : HL 8  was synthesized in 60% yield using the same procedure as HL 1  except that 1,3-diiodotoluene was used as starting material.  1 H NMR (CDCl 3 ): 2.28 (s, 6H), 2.32 (s, 6H), 2.44 (s, 3H), 5.98 (s, 2H), 7.26-7.28 (m, 3H). 
         [0038]    HL 9 : A mixture of 3,5-diiodotoluene (1.1 g, 3.0 mmol), 1-methylimidazole (7.5 mmol), Pd(OAc) 2  (5 mg, 0.01 mmol), KI (2.0 g, 12 mmol), and CuI (2.4 g, 12.2 mmol) in degassed DMF (12 mL) was heated under Ar at 140° C. for 10 days. After cooling to room temperature, the mixture was poured into NH 3  solution (10%, 50 mL), and CH 2 Cl 2  (40×3 mL) was added. The organic phase was separated and dried (MgSO 4 ), and the solvent was evaporated. The crude product was purified by chromatograph (silica gel; ethyl acetate/methanol, 4:1) to give ligand HL 9  as a light yellow solid (40%).  1 H NMR (CDCl 3 ): δ2.44 (s, 3H), 3.78 (s, 6H), 6.97 (d, 2H), 7.11 (d, 2H), 7.52 (s, 2H), 7.60 (s, 1H). 
         [0039]    HL 10 : HL 10  was synthesized in 35% yield using the same procedure as HL 1  except that 1,3-dibromopyridine was used as starting material.  1 H NMR (CDCl 3 ): 2.3 (s, 6H), 2.4 (s, 6H), 6.06 (s, 2H), 8.00 (t, 1H), 8.71 (d, 2H). 
         [0040]    HL 11 : HL 11  was synthesized in 35% yield using the same procedure as HL 9  except that 1,3-dibromopyridine was used as starting material. 
         [0041]    Pyridine-containing structures may be similarly synthesized. 
         [0042]    Platinum(II) complexes were prepared from HL 1 -HL 11  as described below. 
         [0043]    Acetic acid (3 mL) and water (0.3 mL) were added to a mixture of the ligand HL n  (e.g., 1.0 mmol) and K 2 PtCl 4  (1 equiv) in a glass vessel with a magnetic stir bar. The vessel was capped, and then the mixture was heated under microwave irradiation for 30-60 minutes. Upon cooling to room temperature, a yellow or yellow-orange precipitate was formed. The precipitate was separated off from the yellow solution, washed sequentially with methanol, water, ethanol, and diethyl ether (e.g., 3×5 mL of each), and dried under vacuum. 
         [0044]    Platinum (II) Ligand chloride (PtL 1-11 Cl) were treated with phenol and potassium hydroxide in acetone to give PtL 1-11 OPh for 2-3 hs after being filtrated, washed by water, acetone, and ether. 
         [0045]      FIG. 3  shows platinum(II) di(2-pyrazolyl)benzene chloride and analogs synthesized from the ligands.  1 H NMR data for these compounds in DMSO or CDCl 3  are listed below. 
         [0046]    PtL 1 Cl:  1 H NMR (DMSO): 6.84 (dd, 2H), 7.37 (t, 1H), 7.48 (d, 2H), 7.93 (d, 2H), 8.91 (d, 2H). 
         [0047]    PtL 2 Cl:  1 H NMR (DMSO): 2.62 (s, 6H), 2.72 (s, 6H), 6.32 (s, 2H), 7.19-7.20 (m, 3H). 
         [0048]    PtL 3 Cl:  1 H NMR (CDCl 3 ): 7.40 (dd, 2H), 7.28 (d, 2H), 7.13 (t, 1H), 6.93 (d, 2H). 
         [0049]    PtL 5 Cl:  1 H NMR (DMSO): 7.28 (t, 1H), 7.95 (d, 2H), 8.14 (d, 2H). 
         [0050]    PtL 8 Cl:  1 H NMR (CDCl 3 ): 2.65 (s, 6H), 2.76 (s, 6H), 6.34 (s, 2H), 7.09 (s, 2H). 
         [0051]    PtL 9 Cl:  1 H NMR (CDCl 3 ): 7.37 (dd, 2H), 7.11 (d, 2H), 6.91 (d, 2H), 4.04 (s, 6H), 2.34 (s, 3H). 
         [0052]    PtL 10 Cl:  1 H NMR (CDCl 3 ): δ2.78 (s, 6H), 2.79 (s, 6H), 6.11 (s, 2H), 8.27 (s, 2H). 
         [0053]    PtL 2 OPh:  1 H NMR (CDCl 3 ): 7.07-7.16 (m, 5H), 7.02 (d, 2H), 6.49 (t, 1h), 6.01 (s, 2H), 2.71 (s, 6H), 2.45 (s, 6H). 
         [0054]    PtL 2 OPhBu-t:  1 H NMR (CDCl 3 ): 7.13 (t, 1H), 7.08 (d, 2H), 7.02 (d, 2H), 7.00 (d, 2H), 6.00 (s, 2H), 2.71 (s, 6H), 2.47 (s, 6H), 1.25 (s, 9H). 
         [0055]    PtL 3 OPh:  1 H NMR (CDCl 3 ): 7.23 (d, 2H), 7.17 (d, 2H), 7.11 (t, 1H), 7.06 (t, 1H), 6.85-6.87 (m, 4H), 6.78 (d, 2H), 3.99 (s, 6H). 
         [0056]      FIGS. 4-12  show photoluminescence spectra for several Pt complexes including PtL 1 Cl, PtL 2 Cl, PtL 3 Cl, PtL 5 Cl, PtL 8 Cl, PtL 9 Cl, PtL 11 Cl and PtL 2 OPh. 
         [0057]      FIG. 4  shows a room temperature emission spectrum of platinum(II) di(2-pyrazolyl)benzene chloride in dichloromethane. 
         [0058]      FIG. 5  shows room temperature (plot 500) and 77K (plot 502) emission spectra of platinum(II) di(3,5-dimethyl-2-pyrazolyl)benzene chloride in solution. 
         [0059]      FIG. 6  shows a room temperature emission spectrum of platinum(II) di(3,5-dimethyl-2-pyrazolyl)benzene chloride in thin film of poly(methyl methacrylate) (PMMA). 
         [0060]      FIG. 7  shows a room temperature emission spectrum of platinum(II) di(3,5-dimethyl-2-pyrazolyl)benzene phenoxide in a thin film of poly(carbonate). 
         [0061]      FIG. 8  shows a room temperature emission spectrum of platinum(II) di(3,5-dimethyl-2-pyrazolyl)toluene chloride in a thin film of poly(methyl methacrylate) (PMMA). 
         [0062]      FIG. 9  shows a room temperature emission spectrum of platinum(II) di(methyl-imidazolyl)benzene chloride in a solution of dichloromethane. 
         [0063]      FIG. 10  shows a room temperature emission spectrum of platinum(II) di(methyl-imidazolyl)benzene chloride in a thin film of poly(methyl methacrylate) (PMMA). 
         [0064]      FIG. 11A  shows a room temperature emission spectrum of platinum(II) di(methyl-imidazolyl)toluene chloride in a thin film of poly(methyl methacrylate) (PMMA). 
         [0065]      FIG. 11B  shows a 77K emission spectrum of platinum(II) di(methyl-imidazolyl)pyridine chloride in a solution of 2-methyl-tetrahydrofuran. 
         [0066]      FIG. 12  shows a room temperature emission spectrum of platinum(II) di(thiazolyl)(4,6-difluoro-benzene) chloride in a solution of dichloromethane. 
         [0067]    As seen in these spectra, these complexes provide the capability of tuning the emission energy of platinum(II) complexes over a range between ultraviolet and near-infrared, as well as improved emission in the blue wavelength range. These complexes can be used as luminescent labels, emitters for OLEDs, and other applications that benefit from efficient blue emission and high stability (longer lifetime). 
         [0068]    A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention.