# Patent

## Title
Luminescent compounds with carbene ligands

## Abstract

An organic light emitting device is provided. The device has an anode, a cathode and an organic layer disposed between the anode and the cathode. The organic layer comprises a compound further comprising one or more carbene ligands coordinated to a metal center.

## Background
FIELD OF THE INVENTION
The present invention relates to organic light emitting devices (OLEDs), and more specifically to phosphorescent organic materials used in such devices. More specifically, the present invention relates to carbene-metal complexes incorporated into OLEDs.
The claimed invention was made by, on behalf of, and/or in connection with one or more of the following parties to a joint university-corporation research agreement: Princeton University, The University of Southern California, and Universal Display Corporation. The agreement was in effect on and before the date the claimed invention was made, and the claimed invention was made as a result of activities undertaken within the scope of the agreement.
BACKGROUND
Opto-electronic devices that make use of organic materials are becoming increasingly desirable for a number of reasons. Many of the materials used to make such devices are relatively inexpensive, so organic opto-electronic devices have the potential for cost advantages over inorganic devices. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on a flexible substrate. Examples of organic opto-electronic devices include organic light emitting devices (OLEDs), organic phototransistors, organic photovoltaic cells, and organic photodetectors. For OLEDs, the organic materials may have performance advantages over conventional materials. For example, the wavelength at which an organic emissive layer emits light may generally be readily tuned with appropriate dopants.
As used herein, the term “organic” includes polymeric materials as well as small molecule organic materials that may be used to fabricate organic opto-electronic devices. “Small molecule” refers to any organic material that is not a polymer, and “small molecules” may actually be quite large. Small molecules may include repeat units in some circumstances. For example, using a long chain alkyl group as a substituent does not remove a molecule from the “small molecule” class. Small molecules may also be incorporated into polymers, for example as a pendent group on a polymer backbone or as a part of the backbone. Small molecules may also serve as the core moiety of a dendrimer, which consists of a series of chemical shells built on the core moiety. The core moiety of a dendrimer may be an fluorescent or phosphorescent small molecule emitter. A dendrimer may be a “small molecule,” and it is believed that all dendrimers currently used in the field of OLEDs are small molecules.
OLEDs make use of thin organic films that emit light when voltage is applied across the device. OLEDs are becoming an increasingly interesting technology for use in applications such as flat panel displays, illumination, and backlighting. Several OLED materials and configurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and 5,707,745, which are incorporated herein by reference in their entirety.
OLED devices are generally (but not always) intended to emit light through at least one of the electrodes, and one or more transparent electrodes may be useful in an organic opto-electronic devices. For example, a transparent electrode material, such as indium tin oxide (ITO), may be used as the bottom electrode. A transparent top electrode, such as disclosed in U.S. Pat. Nos. 5,703,436 and 5,707,745, which are incorporated by reference in their entireties, may also be used. For a device intended to emit light only through the bottom electrode, the top electrode does not need to be transparent, and may be comprised of a thick and reflective metal layer having a high electrical conductivity. Similarly, for a device intended to emit light only through the top electrode, the bottom electrode may be opaque and/or reflective. Where an electrode does not need to be transparent, using a thicker layer may provide better conductivity, and using a reflective electrode may increase the amount of light emitted through the other electrode, by reflecting light back towards the transparent electrode. Fully transparent devices may also be fabricated, where both electrodes are transparent. Side emitting OLEDs may also be fabricated, and one or both electrodes may be opaque or reflective in such devices.
As used herein, “top” means furthest away from the substrate, while “bottom” means closest to the substrate. For example, for a device having two electrodes, the bottom electrode is the electrode closest to the substrate, and is generally the first electrode fabricated. The bottom electrode has two surfaces, a bottom surface closest to the substrate, and a top surface further away from the substrate. Where a first layer is described as “disposed over” a second layer, the first layer is disposed further away from substrate. There may be other layers between the first and second layer, unless it is specified that the first layer is “in physical contact with” the second layer. For example, a cathode may be described as “disposed over” an anode, even though there are various organic layers in between.
As used herein, “solution processible” means capable of being dissolved, dispersed, or transported in and/or deposited from a liquid medium, either in solution or suspension form.
The carbene ligand has been well known in organometallic chemistry, and is used to generate a wide range of thermally stable catalytic materials. The carbene ligands have been employed both as active groups, directly engaged in the catalytic reactions, and serving a role of stabilizing the metal in a particular oxidation state or coordination geometry. However, applications of carbene ligands are not well known in photochemistry and have yet to be used as electroluminescent compounds.
One issue with many existing organic electroluminescent compounds is that they are not sufficiently stable for use in commercial devices. An object of the invention is to provide a class of organic emissive compounds having improved stability.
In addition, prior art compounds do not include compounds that are stable emitters for high energy spectra, such as a blue spectra. An object of the invention is to provide a class of organic emissive compounds that can emit light with various spectra, including high energy spectra such as blue, in a stable manner.
SUMMARY OF THE INVENTION
An organic light emitting device is provided. The device has an anode, a cathode and an organic layer disposed between the anode and the cathode. The organic layer comprises a compound further comprising one or more carbene ligands coordinated to a metal center.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows an organic light emitting device having separate electron transport, hole transport, and emissive layers, as well as other layers.
FIG. 2 shows an inverted organic light emitting device that does not have a separate electron transport layer.
FIG. 3 shows the 1H NMR spectra of mer-(F2ppz)2Ir(1-Ph-3-Me-imid) in CDCl3.
FIG. 4 shows the 1H NMR spectra of mer-(tpy)2Ir(1-Ph-3-Me-imid) in CDCl3.
FIG. 5 shows the 1H NMR spectra of fac-(tpy)2Ir(1-Ph-3-Me-imid) in CDCl3.
FIG. 6 shows the plot of current (μA) vs. voltage (V) of a mer-(tpy)2Ir(1-Ph-3-Me-imid) device with ferrocene as an internal reference. A solvent of DMF with 0.1M Bu4N+PF6− is used.
FIG. 7 shows the plot of current (μA) vs. voltage (V) of a fac-(tpy)2Ir(1-Ph-3-Me-imid) device with ferrocene as an internal reference. A solvent of DMF with 0.1M Bu4N+PF6− is used.
FIG. 8 shows the absorption spectra of fac-(tpy)2Ir(1-Ph-3-Me-imid) and mer-(tpy)2Ir(1-Ph-3-Me-imid) in CH2Cl2.
FIG. 9 shows the emission spectra of mer-(tpy)2Ir(1-Ph-3-Me-imid) in 2-MeTHF at room temperature and at 77K. The compound exhibits lifetimes of 1.7 μs at room temperature and 3.3 μs at 77K.
FIG. 10 shows the emission spectra of fac-(tpy)2Ir(1-Ph-3-Me-imid) in 2-MeTHF at room temperature and at 77K. The compound exhibits lifetimes of 1.7 μs at room temperature and 3.3 μs at 77K.
FIG. 11 shows the 1H NMR spectra of [(1-Ph-3-Me-imid)2IrCl]2 in CDCl3.
FIG. 12 shows the 1H NMR spectra of (1-Ph-3-Me-imid)2Ir(t-Bu-bpy)+ in CDCl3.
FIG. 13 shows the absorption spectra of (1-Ph-3-Me-imid)2Ir(t-Bu-bpy)+ in CH2Cl2.
FIG. 14 shows the emission spectra of (1-Ph-3-Me-imid)2Ir(t-Bu-bpy)+ in 2-MeTHF at 77K and (1-Ph-3-Me-imid)2Ir(t-Bu-bpy)+ in CH2Cl2 at room temperature. The compound exhibits lifetimes of 0.70 μs at room temperature and 6.0 μs at 77K.
FIG. 15 shows the 1H NMR spectra of mer-Ir(1-Ph-3-Me-imid)3 in CDCl3.
FIG. 16 shows the 13C NMR spectra of mer-Ir(1-Ph-3-Me-imid)3 in CDCl3.
FIG. 17 shows the plot of current (μA) vs. voltage (V) of a mer-Ir(1-Ph-3-Me-imid)3 device with ferrocene as an internal reference. A solvent of DMF with 0.1M Bu4N+PF6− is used.
FIG. 18 shows the emission spectra of mer-Ir(1-Ph-3-Me-imid)3 in 2-MeTHF at room temperature and at 77K.
FIG. 19 shows the 1H NMR spectra of fac-Ir(1-Ph-3-Me-imid)3 in CDCl3.
FIG. 20 shows the absorption spectra of fac-Ir(1-Ph-3-Me-imid)3 in CH2Cl2.
FIG. 21 shows the emission spectra of fac-Ir(1-Ph-3-Me-imid)3 in 2-MeTHF at room temperature and at 77K. The device exhibits lifetimes of 0.50 μs at room temperature and 6.8 μs at 77K.
FIG. 22 shows the 1H NMR spectra of 1-Ph-3-Me-benzimid in CDCl3.
FIG. 23 shows the 1H NMR spectra of fac-Ir(1-Ph-3-Me-benzimid)3 in CDCl3.
FIG. 24 shows the plot of current (mA) vs. voltage (V) of a fac-Ir(1-Ph-3-Me-benzimid)3 device with ferrocene as an internal reference. A solvent of anhydrous DMF is used.
FIG. 25 shows the emission spectra of fac-Ir(1-Ph-3-Me-benzimid)3 in 2-MeTHF at room temperature and at 77K. The device emits a spectrum at CIE 0.17, 0.04.
FIG. 26 shows the emission spectra of (Ir-Fl-Me-imidazolate)3 in 2-MeTHF at roomo temperature and at 77K. The device exhibits lifetimes of 5 μs at room temperature and 35 μs at 77K.



DETAILED DESCRIPTION
Generally, an OLED comprises at least one organic layer disposed between and electrically connected to an anode and a cathode. When a current is applied, the anode injects holes and the cathode injects electrons into the organic layer(s). The injected holes and electrons each migrate toward the oppositely charged electrode. When an electron and hole localize on the same molecule, an “exciton,” which is a localized electron-hole pair having an excited energy state, is formed. Light is emitted when the exciton relaxes via a photoemissive mechanism. In some cases, the exciton may be localized on an excimer or an exciplex. Non-radiative mechanisms, such as thermal relaxation, may also occur, but are generally considered undesirable.
The initial OLEDs used emissive molecules that emitted light from their singlet states (“fluorescence”) as disclosed, for example, in U.S. Pat. No. 4,769,292, which is incorporated by reference in its entirety. Fluorescent emission generally occurs in a time frame of less than 10 nanoseconds.
More recently, OLEDs having emissive materials that emit light from triplet states (“phosphorescence”) have been demonstrated. Baldo et al., “Highly Efficient Phosphorescent Emission from Organic Electroluminescent Devices,” Nature, vol. 395, 151-154, 1998; (“Baldo-I”) and Baldo et al., “Very high-efficiency green organic light-emitting devices based on electrophosphorescence,” Appl. Phys. Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporated by reference in their entireties. Phosphorescence may be referred to as a “forbidden” transition because the transition requires a change in spin states, and quantum mechanics indicates that such a transition is not favored. As a result, phosphorescence generally occurs in a time frame exceeding at least 10 nanoseconds, and typically greater than 100 nanoseconds. If the natural radiative lifetime of phosphorescence is too long, triplets may decay by a non-radiative mechanism, such that no light is emitted. Organic phosphorescence is also often observed in molecules containing heteroatoms with unshared pairs of electrons at very low temperatures. 2,2′-bipyridine is such a molecule. Non-radiative decay mechanisms are typically temperature dependent, such that a material that exhibits phosphorescence at liquid nitrogen temperatures may not exhibit phosphorescence at room temperature. But, as demonstrated by Baldo, this problem may be addressed by selecting phosphorescent compounds that do phosphoresce at room temperature. Representative emissive layers include doped or un-doped phosphorescent organo-metallic materials such as disclosed in U.S. Pat. Nos. 6,303,238 and 6,310,360; U.S. Patent Application Publication Nos. 2002-0034656; 2002-0182441; amd 2003-0072964; and WO-02/074015.
Generally, the excitons in an OLED are believed to be created in a ratio of about 3:1, i.e., approximately 75% triplets and 25% singlets. See, Adachi et al., “Nearly 100% Internal Phosphorescent Efficiency In An Organic Light Emitting Device,” J. Appl. Phys., 90, 5048 (2001), which is incorporated by reference in its entirety. In many cases, singlet excitons may readily transfer their energy to triplet excited states via “intersystem crossing,” whereas triplet excitons may not readily transfer their energy to singlet excited states. As a result, 100% internal quantum efficiency is theoretically possible with phosphorescent OLEDs. In a fluorescent device, the energy of triplet excitons is generally lost to radiationless decay processes that heat-up the device, resulting in much lower internal quantum efficiencies. OLEDs utilizing phosphorescent materials that emit from triplet excited states are disclosed, for example, in U.S. Pat. No. 6,303,238, which is incorporated by reference in its entirety.
Phosphorescence may be preceded by a transition from a triplet excited state to an intermediate non-triplet state from which the emissive decay occurs. For example, organic molecules coordinated to lanthanide elements often phosphoresce from excited states localized on the lanthanide metal. However, such materials do not phosphoresce directly from a triplet excited state but instead emit from an atomic excited state centered on the lanthanide metal ion. The europium diketonate complexes illustrate one group of these types of species.
Phosphorescence from triplets can be enhanced over fluorescence by confining, preferably through bonding, the organic molecule in close proximity to an atom of high atomic number. This phenomenon, called the heavy atom effect, is created by a mechanism known as spin-orbit coupling. Such a phosphorescent transition may be observed from an excited metal-to-ligand charge transfer (MLCT) state of an organometallic molecule such as tris(2-phenylpyridine)iridium(III).
As used herein, the term “triplet energy” refers to an energy corresponding to the highest energy feature discernable in the phosphorescence spectrum of a given material. The highest energy feature is not necessarily the peak having the greatest intensity in the phosphorescence spectrum, and could, for example, be a local maximum of a clear shoulder on the high energy side of such a peak.
FIG. 1 shows an organic light emitting device 100. The figures are not necessarily drawn to scale. Device 100 may include a substrate 110, an anode 115, a hole injection layer 120, a hole transport layer 125, an electron blocking layer 130, an emissive layer 135, a hole blocking layer 140, an electron transport layer 145, an electron injection layer 150, a protective layer 155, and a cathode 160. Cathode 160 is a compound cathode having a first conductive layer 162 and a second conductive layer 164. Device 100 may be fabricated by depositing the layers described, in order.
Substrate 110 may be any suitable substrate that provides desired structural properties. Substrate 110 may be flexible or rigid. Substrate 110 may be transparent, translucent or opaque. Plastic and glass are examples of preferred rigid substrate materials. Plastic and metal foils are examples of preferred flexible substrate materials. Substrate 110 may be a semiconductor material in order to facilitate the fabrication of circuitry. For example, substrate 110 may be a silicon wafer upon which circuits are fabricated, capable of controlling OLEDs subsequently deposited on the substrate. Other substrates may be used. The material and thickness of substrate 110 may be chosen to obtain desired structural and optical properties.
Anode 115 may be any suitable anode that is sufficiently conductive to transport holes to the organic layers. The material of anode 115 preferably has a work function higher than about 4 eV (a “high work function material”). Preferred anode materials include conductive metal oxides, such as indium tin oxide (ITO) and indium zinc oxide (IZO), aluminum zinc oxide (AlZnO), and metals. Anode 115 (and substrate 110) may be sufficiently transparent to create a bottom-emitting device. A preferred transparent substrate and anode combination is commercially available ITO (anode) deposited on glass or plastic (substrate). A flexible and transparent substrate-anode combination is disclosed in U.S. Pat. Nos. 5,844,363 and 6,602,540 B2, which are incorporated by reference in their entirety. Anode 115 may be opaque and/or reflective. A reflective anode 115 may be preferred for some top-emitting devices, to increase the amount of light emitted from the top of the device. The material and thickness of anode 115 may be chosen to obtain desired conductive and optical properties. Where anode 115 is transparent, there may be a range of thickness for a particular material that is thick enough to provide the desired conductivity, yet thin enough to provide the desired degree of transparency. Other anode materials and structures may be used.
Hole transport layer 125 may include a material capable of transporting holes. Hole transport layer 130 may be intrinsic (undoped), or doped. Doping may be used to enhance conductivity. a-NPD and TPD are examples of intrinsic hole transport layers. An example of a p-doped hole transport layer is m-MTDATA doped with F4-TCNQ at a molar ratio of 50:1, as disclosed in U.S. Patent Application Publication No. 2002-0071963 A1 to Forrest et al., which is incorporated by reference in its entirety. Other hole transport layers may be used.
Emissive layer 135 may include an organic material capable of emitting light when a current is passed between anode 115 and cathode 160. Preferably, emissive layer 135 contains a phosphorescent emissive material, although fluorescent emissive materials may also be used. Phosphorescent materials are preferred because of the higher luminescent efficiencies associated with such materials. Emissive layer 135 may also comprise a host material capable of transporting electrons and/or holes, doped with an emissive material that may trap electrons, holes, and/or excitons, such that excitons relax from the emissive material via a photoemissive mechanism. Emissive layer 135 may comprise a single material that combines transport and emissive properties. Whether the emissive material is a dopant or a major constituent, emissive layer 135 may comprise other materials, such as dopants that tune the emission of the emissive material. Emissive layer 135 may include a plurality of emissive materials capable of, in combination, emitting a desired spectrum of light. Examples of phosphorescent emissive materials include Ir(ppy)3. Examples of fluorescent emissive materials include DCM and DMQA. Examples of host materials include Alq3, CBP and mCP. Examples of emissive and host materials are disclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which is incorporated by reference in its entirety. Emissive material may be included in emissive layer 135 in a number of ways. For example, an emissive small molecule may be incorporated into a polymer. This may be accomplished by several ways: by doping the small molecule into the polymer either as a separate and distinct molecular species; or by incorporating the small molecule into the backbone of the polymer, so as to form a co-polymer; or by bonding the small molecule as a pendant group on the polymer. Other emissive layer materials and structures may be used. For example, a small molecule emissive material may be present as the core of a dendrimer.
Electron transport layer 140 may include a material capable of transporting electrons. Electron transport layer 140 may be intrinsic (undoped), or doped. Doping may be used to enhance conductivity. Alq3 is an example of an intrinsic electron transport layer. An example of an n-doped electron transport layer is BPhen doped with Li at a molar ratio of 1:1, as disclosed in U.S. Patent Application Publication No. 2002-0071963 A1 to Forrest et al., which is incorporated by reference in its entirety. Other electron transport layers may be used.
The charge carrying component of the electron transport layer may be selected such that electrons can be efficiently injected from the cathode into the LUMO (Lowest Unoccupied Molecular Orbital) level of the electron transport layer. The “charge carrying component” is the material responsible for the LUMO that actually transports electrons. This component may be the base material, or it may be a dopant. The LUMO level of an organic material may be generally characterized by the electron affinity of that material and the relative electron injection efficiency of a cathode may be generally characterized in terms of the work function of the cathode material. This means that the preferred properties of an electron transport layer and the adjacent cathode may be specified in terms of the electron affinity of the charge carrying component of the ETL and the work function of the cathode material. In particular, so as to achieve high electron injection efficiency, the work function of the cathode material is preferably not greater than the electron affinity of the charge carrying component of the electron transport layer by more than about 0.75 eV, more preferably, by not more than about 0.5 eV. Similar considerations apply to any layer into which electrons are being injected.
Cathode 160 may be any suitable material or combination of materials known to the art, such that cathode 160 is capable of conducting electrons and injecting them into the organic layers of device 100. Cathode 160 may be transparent or opaque, and may be reflective. Metals and metal oxides are examples of suitable cathode materials. Cathode 160 may be a single layer, or may have a compound structure. FIG. 1 shows a compound cathode 160 having a thin metal layer 162 and a thicker conductive metal oxide layer 164. In a compound cathode, preferred materials for the thicker layer 164 include ITO, IZO, and other materials known to the art. U.S. Pat. Nos. 5,703,436, 5,707,745, 6,548,956 B2, and 6,576,134 B2, which are incorporated by reference in their entireties, disclose examples of cathodes including compound cathodes having a thin layer of metal such as Mg:Ag with an overlying transparent, electrically-conductive, sputter-deposited ITO layer. The part of cathode 160 that is in contact with the underlying organic layer, whether it is a single layer cathode 160, the thin metal layer 162 of a compound cathode, or some other part, is preferably made of a material having a work function lower than about 4 eV (a “low work function material”). Other cathode materials and structures may be used.
Blocking layers may be used to reduce the number of charge carriers (electrons or holes) and/or excitons that leave the emissive layer. An electron blocking layer 130 may be disposed between emissive layer 135 and the hole transport layer 125, to block electrons from leaving emissive layer 135 in the direction of hole transport layer 125. Similarly, a hole blocking layer 140 may be disposed between emissive layer 135 and electron transport layer 145, to block holes from leaving emissive layer 135 in the direction of electron transport layer 140. Blocking layers may also be used to block excitons from diffusing out of the emissive layer. The theory and use of blocking layers is described in more detail in U.S. Pat. No. 6,097,147 and U.S. Patent Application Publication No. 2002-0071963 A1 to Forrest et al., which are incorporated by reference in their entireties.
As used herein, the term “blocking layer” means that the layer provides a barrier that significantly inhibits transport of charge carriers and/or excitons through the device, without suggesting that the layer necessarily completely blocks the charge carriers and/or excitons. The presence of such a blocking layer in a device may result in substantially higher efficiencies as compared to a similar device lacking a blocking layer. Also, a blocking layer may be used to confine emission to a desired region of an OLED.
Generally, injection layers are comprised of a material that may improve the injection of charge carriers from one layer, such as an electrode or an organic layer, into an adjacent organic layer. Injection layers may also perform a charge transport function. In device 100, hole injection layer 120 may be any layer that improves the injection of holes from anode 115 into hole transport layer 125. CuPc is an example of a material that may be used as a hole injection layer from an ITO anode 115, and other anodes. In device 100, electron injection layer 150 may be any layer that improves the injection of electrons into electron transport layer 145. LiF/Al is an example of a material that may be used as an electron injection layer into an electron transport layer from an adjacent layer. Other materials or combinations of materials may be used for injection layers. Depending upon the configuration of a particular device, injection layers may be disposed at locations different than those shown in device 100. More examples of injection layers are provided in U.S. patent application Ser. No. 09/931,948 to Lu et al., which is incorporated by reference in its entirety. A hole injection layer may comprise a solution deposited material, such as a spin-coated polymer, e.g., PEDOT:PSS, or it may be a vapor deposited small molecule material, e.g., CuPc or MTDATA.
A hole injection layer (HIL) may planarize or wet the anode surface so as to provide efficient hole injection from the anode into the hole injecting material. A hole injection layer may also have a charge carrying component having HOMO (Highest Occupied Molecular Orbital) energy levels that favorably match up, as defined by their herein-described relative ionization potential (IP) energies, with the adjacent anode layer on one side of the HIL and the hole transporting layer on the opposite side of the HIL. The “charge carrying component” is the material responsible for the HOMO that actually transports holes. This component may be the base material of the HIL, or it may be a dopant. Using a doped HIL allows the dopant to be selected for its electrical properties, and the host to be selected for morphological properties such as wetting, flexibility, toughness, etc. Preferred properties for the HIL material are such that holes can be efficiently injected from the anode into the HIL material. In particular, the charge carrying component of the HIL preferably has an IP not more than about 0.7 eV greater that the IP of the anode material. More preferably, the charge carrying component has an IP not more than about 0.5 eV greater than the anode material. Similar considerations apply to any layer into which holes are being injected. HIL materials are further distinguished from conventional hole transporting materials that are typically used in the hole transporting layer of an OLED in that such HIL materials may have a hole conductivity that is substantially less than the hole conductivity of conventional hole transporting materials. The thickness of the HIL of the present invention may be thick enough to help planarize or wet the surface of the anode layer. For example, an HIL thickness of as little as 10 nm may be acceptable for a very smooth anode surface. However, since anode surfaces tend to be very rough, a thickness for the HIL of up to 50 nm may be desired in some cases.
A protective layer may be used to protect underlying layers during subsequent fabrication processes. For example, the processes used to fabricate metal or metal oxide top electrodes may damage organic layers, and a protective layer may be used to reduce or eliminate such damage. In device 100, protective layer 155 may reduce damage to underlying organic layers during the fabrication of cathode 160. Preferably, a protective layer has a high carrier mobility for the type of carrier that it transports (electrons in device 100), such that it does not significantly increase the operating voltage of device 100. CuPc, BCP, and various metal phthalocyanines are examples of materials that may be used in protective layers. Other materials or combinations of materials may be used. The thickness of protective layer 155 is preferably thick enough that there is little or no damage to underlying layers due to fabrication processes that occur after organic protective layer 160 is deposited, yet not so thick as to significantly increase the operating voltage of device 100. Protective layer 155 may be doped to increase its conductivity. For example, a CuPc or BCP protective layer 160 may be doped with Li. A more detailed description of protective layers may be found in U.S. patent application Ser. No. 09/931,948 to Lu et al., which is incorporated by reference in its entirety.
FIG. 2 shows an inverted OLED 200. The device includes a substrate 210, an cathode 215, an emissive layer 220, a hole transport layer 225, and an anode 230. Device 200 may be fabricated by depositing the layers described, in order. Because the most common OLED configuration has a cathode disposed over the anode, and device 200 has cathode 215 disposed under anode 230, device 200 may be referred to as an “inverted” OLED. Materials similar to those described with respect to device 100 may be used in the corresponding layers of device 200. FIG. 2 provides one example of how some layers may be omitted from the structure of device 100.
The simple layered structure illustrated in FIGS. 1 and 2 is provided by way of non-limiting example, and it is understood that embodiments of the invention may be used in connection with a wide variety of other structures. The specific materials and structures described are exemplary in nature, and other materials and structures may be used. Functional OLEDs may be achieved by combining the various layers described in different ways, or layers may be omitted entirely, based on design, performance, and cost factors. Other layers not specifically described may also be included. Materials other than those specifically described may be used. Although many of the examples provided herein describe various layers as comprising a single material, it is understood that combinations of materials, such as a mixture of host and dopant, or more generally a mixture, may be used. Also, the layers may have various sublayers. The names given to the various layers herein are not intended to be strictly limiting. For example, in device 200, hole transport layer 225 transports holes and injects holes into emissive layer 220, and may be described as a hole transport layer or a hole injection layer. In one embodiment, an OLED may be described as having an “organic layer” disposed between a cathode and an anode. This organic layer may comprise a single layer, or may further comprise multiple layers of different organic materials as described, for example, with respect to FIGS. 1 and 2.
Structures and materials not specifically described may also be used, such as OLEDs comprised of polymeric materials (PLEDs) such as disclosed in U.S. Pat. No. 5,247,190, Friend et al., which is incorporated by reference in its entirety. By way of further example, OLEDs having a single organic layer may be used. OLEDs may be stacked, for example as described in U.S. Pat. No. 5,707,745 to Forrest et al, which is incorporated by reference in its entirety. The OLED structure may deviate from the simple layered structure illustrated in FIGS. 1 and 2. For example, the substrate may include an angled reflective surface to improve out-coupling, such as a mesa structure as described in U.S. Pat. No. 6,091,195 to Forrest et al., and/or a pit structure as described in U.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated by reference in their entireties.
Unless otherwise specified, any of the layers of the various embodiments may be deposited by any suitable method. For the organic layers, preferred methods include thermal evaporation, ink-jet, such as described in U.S. Pat. Nos. 6,013,982 and 6,087,196, which are incorporated by reference in their entireties, organic vapor phase deposition (OVPD), such as described in U.S. Pat. No. 6,337,102 to Forrest et al., which is incorporated by reference in its entirety, and deposition by organic vapor jet printing (OVJP), such as described in U.S. patent application Ser. No. 10/233,470, which is incorporated by reference in its entirety. Other suitable deposition methods include spin coating and other solution based processes. Solution based processes are preferably carried out in nitrogen or an inert atmosphere. For the other layers, preferred methods include thermal evaporation. Preferred patterning methods include deposition through a mask, cold welding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819, which are incorporated by reference in their entireties, and patterning associated with some of the deposition methods such as ink-jet and OVJD. Other methods may also be used. The materials to be deposited may be modified to make them compatible with a particular deposition method. For example, substituents such as alkyl and aryl groups, branched or unbranched, and preferably containing at least 3 carbons, may be used in small molecules to enhance their ability to undergo solution processing. Substituents having 20 carbons or more may be used, and 3-20 carbons is a preferred range. Materials with asymmetric structures may have better solution processibility than those having symmetric structures, because asymmetric materials may have a lower tendency to recrystallize. Dendrimer substituents may be used to enhance the ability of small molecules to undergo solution processing.
Devices fabricated in accordance with embodiments of the invention may be incorporated into a wide variety of consumer products, including flat panel displays, computer monitors, televisions, billboards, lights for interior or exterior illumination and/or signaling, heads up displays, fully transparent displays, flexible displays, laser printers, telephones, cell phones, personal digital assistants (PDAs), laptop computers, digital cameras, camcorders, viewfinders, micro-displays, vehicles, a large area wall, theater or stadium screen, or a sign. Various control mechanisms may be used to control devices fabricated in accordance with the present invention, including passive matrix and active matrix. Many of the devices are intended for use in a temperature range comfortable to humans, such as 18 degrees C. to 30 degrees C., and more preferably at room temperature (20-25 degrees C.).
The materials and structures described herein may have applications in devices other than OLEDs. For example, other optoelectronic devices such as organic solar cells and organic photodetectors may employ the materials and structures. More generally, organic devices, such as organic transistors, may employ the materials and structures.
A compound comprising a carbene ligand bound to a metal center is provided. Carbene compounds include small molecules, dendrimers, and polymers that include a carbene-metal bond. In one embodiment, the compound is a phosphorescent emissive material, preferably a dopant. The compound may also be doped into a wide band gap host material such as disclosed in U.S. patent application Ser. No. 10/680,066, which is incorporated by reference in its entirety, or it may be doped into an inert wide band gap host such as disclosed in WO-074015, which is incorporated by reference in its entirety.
In another embodiment, the metal-carbene compound is a host material in an emissive layer. For example, the metal-carbene compound may be used as a high energy host materials for doped blue devices. The dopant in this case could be a triplet emitter or a singlet emitter (using phosphor sensitized fluorescence). Additionally, the high band gap of metal-carbene compounds may make these materials effective in carrier blocking and transporting layers. It is believed that metal-carbene compounds described herein have improved thermal stability when incorporated into an organic light emitting device due to the carbene-metal bond, as compared to prior art compounds without a carbene-metal bond.
As used herein, the term “carbene” refers to compounds having a divalent carbon atom with only six electrons in its valence shell when not coordinated to a metal. A useful exercise to determine whether a ligand includes a carbene-metal bond is to mentally deconstruct the complex as a metal fragment and a ligand, and to then determine whether a carbon atom in the ligand that was previously bound to the metal is a neutral divalent carbon atom in the deconstructed state. The resonance forms of a preferred embodiment may be shown as:




This definition of carbene is not limited to metal-carbene complexes synthesized from carbenes, but is rather intended to address the orbital structure and electron distribution associated with the carbon atom that is bound to the metal. The definition recognizes that the “carbene” may not technically be divalent when bound to the metal, but it would be divalent if it were detached from the metal. Although many such compounds are synthesized by first synthesizing a carbene and then binding it to a metal, the definition is intended to encompass compounds synthesized by other methods that have a similar orbital structure and electron configuration. Lowry & Richardson, Mechanism and Theory in Organic Chemistry 256 (Harper & Row, 1976) defines “carbene” in a way that is consistent with the way the term is used herein. Some references may define “carbene” as a carbon ligand that forms a double bond to a metal. While this definition is not being used in the present application, there may be some overlap between the two definitions.

The term “organometallic” as used herein is as generally understood by one of ordinary skill in the art and as given, for example, in “Inorganic Chemistry” (2nd Edition) by Gary L. Miessler and Donald A. Tarr, Pentice-Hall (1998). Thus, the term organometallic refers to compounds which have an organic group bonded to a metal through a carbon-metal bond. This class does not include per se coordination compounds, which are substances having only donor bonds from heteroatoms, such as metal complexes of anines, halides, pseudohalides (CN, etc.), and the like. In practice organometallic compounds generally comprise, in addition to one or more carbon-metal bonds to an organic species, one or more donor bonds from a heteroatom. The carbon-metal bond to an organic species refers to a direct bond between a metal and a carbon atom of an organic group, such as phenyl, alkyl, alkenyl, etc., but does not refer to a metal bond to an “inorganic carbon,” such as the carbon of CN.
Carbene ligands are especially desirable in OLED applications due to the high thermal stability exhibited by metal-carbene complexes. It is believed that the carbene, which behaves much as an electron donative group, generally bonds strongly to the metals, thus forming a more thermally stable complex than, for example, previous cyclometallated complexes used as phosphorescent emitters. It is also believed that carbene analogs of ligands employed in prior phosphorescent emissive materials (for example the phenylpyridine or Irppy, etc.) may exhibit greater stability and emit at substantially higher energy than their prior art analogs.
As used herein, a “non-carbene analog” of a metal carbene compound refers to ligands in the prior art having a substantially similar chemical structure to the metal-carbene compound, but unlike the carbene compounds of the present invention, which features a carbene-metal bond, the analog has some other bond, such as a carbon-metal or a nitrogen-metal bond, in place of the carbene-metal bond. For example, Ir(ppz)3 has a nitrogen in each ligand bound to the Ir. Ir(1-phenylimidazolin-2-ylidene) is analogous to Ir(ppz)3 where the nitrogen bound to the Ir has been replaced with a carbene bound to the Ir, and where the atoms surrounding the carbene have been changed to make the carbon a carbene. Thus, embodiments of the present invention include metal-carbene complexes (e.g. Ir(1-phenylimidazolin-2-ylidene) with similar structures to prior art emissive compounds (e.g. Ir(ppz)3).
Examples of prior art emissive compounds include Ir(ppy)3 and Ir(ppz)3, discussed above. Other examples are disclosed in the references below, which are incorporated herein by reference in their entirety. In preferred embodiments, the carbene ligands are imidazoles, pyrazoles, benzimidazoles, and pyrroles.
It is believed that the carbene-metal bond in Ir(1-Ph-3-Me-imid)3 is stronger than the N-metal bond in Irppz. Moreover, due to the nature of a carbene-metal bond, it is believed that replacing a carbon-metal bond or nitrogen-metal bond in existing emissive organometallic molecules with a carbene-metal bond (making other changes as needed to make the carbon atom a carbene) may result in an emissive molecule that is more stable than the non-carbene analog, and that has stronger spin-orbit coupling. It is further believed that the emissive spectra of the molecule including a carbene may be different from the emissive spectra of the analog without a carbene.
Metal-carbene complexes may be tuned to emit a wide variety of spectra from the near-ultraviolet across the entire visible spectra by the selection of substituents and/or chemical groups on the ligand(s). More significantly, it may now be possible to obtain saturated blue color emissions with peak wavelengths at about 450 nm. Because it is believed to be materially easier to reduce than to increase the triplet energy by tuning an emissive compound, the ability to make stable blue emitters at such high energies would also allow for the possibility of obtaining any color by reducing the energy so as to red-shift the emission. For example, FIG. 18 shows that Ir(1-Ph-3-Me-imid)3, which is a preferred embodiment of this invention, in a 2-MeTHF solution emits in the near-UV spectra at a wavelength of about 380 nm at 77 K and at room temperature. The substitution of a fluorenyl group for the phenyl group attached to the methylimidazole results in a red-shift in the emission as shown in FIG. 26. Thus, FIG. 26 shows Ir-(FlMeImidazole)3, which is another embodiment of this invention, to emit at the visible part of the spectra at a wavelength of 462 nm at 77 K and at 466 nm at room temperature.
The appropriate selection of substituents and/or chemical groups attached to carbene ligands may also minimize quantum efficiency losses associated with increasing temperatures. The observable difference in lifetime measurements between emission at room temperature and at low temperatures (e.g. 77 K) is believed to be attributed to non-radiative quenching mechanisms that compete with phosphorescent emission. Such quenching mechanisms are further believed to be thermally activated, and consequently, at cooler temperatures of about 77 K, where energy loss due to quenching is not an issue, quantum efficiency is about 100%. For example, FIG. 21 shows the emission spectra of fac-Ir(1-Ph-3-Me-imid)3 in 2-MeTHF. The compound exhibits a lifetime of 6.8 μs at 77 K and 0.50 μs at room temperature, and the difference may be attributed to quenching mechanisms. It is believed that appropriate substituents on the carbene ligand may increase quantum efficiency at room temperature and correspondingly show longer lifetimes.
Due to the nature of the carbene-metal bond, the emission of a carbene analog may be substantially different from that of its non-carbene analog, and the emission of the carbene analog may be stable and at a higher energy than previously obtainable with stable non-carbene compounds. Embodiments of the present invention shown in FIGS. 18, 21, 25, and 26, show higher energy emissions than have previously been obtained with other phosphorescent organometallic emissive materials.
The strong metal-carbon bond is also believed to lead to greater spin-orbit coupling in metal carbene complexes. Moreover, the triplet energy of coordinated carbenes are shown to be significantly higher than pyridine analogs. FIG. 18 shows the emission spectra of mer-Ir(1-Ph-3-Me-imid)3, which is one of the embodiments of the invention. The emission is shown to be in the near-ultraviolet range of the spectrum even at room temperature. It is believed herein that other metal carbene complexes may be capable of emitting at similarly high energies due to the strong metal-ligand bond associated with carbene ligands.
The stability of metal-carbene complexes may also allow increased versatility in the types of ligands and metals that may be used as phosphorescent emitters in OLEDs. The strong metal carbene bond may allow a variety of metals to form useful phosphorescent complexes with carbene ligands to give novel emissive compounds. For example, one embodiment includes gold bonded to a carbene ligand. Additionally, although cyclometallated complexes are preferred embodiments, the present invention is not limited to such embodiments. The increased strength of a metal-carbene bond, as compared to other types of bonds with metal, may make monodentate ligands feasible for use as emissive materials. Until recently, bidentate ligands were strongly preferred due to stability concerns. Thus, embodiments include monodentate carbene ligands as well as bidentate. Embodiments also include tridentate carbene ligands, which may be quite stable, and many examples are found in the art, such as those disclosed in Koizumi et al., Organometallics 2003, 22, 970-975. Other embodiments may also feature a tetradentate ligand, such as porphyrin analogs in which one or more nitrogens are replaced by a carbene, which is disclosed in Bourissou et al. Chem Rev. 2000, 100, 39-91. Still other embodiments may include metallaquinone carbenes, which are compounds in which one of the oxygen atoms of a quinone has been replaced by a metal, such as those disclosed in Ashekenazi et al., J. Am. Chem. Soc. 2000, 122, 8797-8798. In addition, The metal-carbene compound may be present as part of a multi-dentate group such as disclosed in U.S. patent application Ser. No. 10/771,423 to Ma et al., which is incorporated by reference in its entirety.
It is believed that many of the (C,C) or (C,N) ligands of many existing electroluminescent compounds may be modified to create an analogous (C,C) ligand including a carbene. Specific non limiting examples of such modification include:

    
    
        (1) the substituents on the carbene-bonded branch of the (C,C)-ligand and the substituents on the mono-anionic-carbon-bonded branch of the (C,C)-ligand may be independently selected from the group consisting of
        
            (a) the substituents on the N-bonded branch of the prior art (C,N)-ligands, such as disclosed in the references listed below, which is typically but not necessarily a pyridine group; and
            (b) the substituents on the mono-anionic-carbon-bonded branch of the prior art (C,N)-ligands, such as disclosed in the references listed below, which is typically but not necessarily a phenyl group;
            (c) and/or a combination thereof; and
        
        
        (2) the compounds including the metal-carbene bonds may further include ancillary ligands selected from the group consisting of the ancillary ligands such as disclosed in the following references:

U.S. Pat. Application Publ. No. 2002-0034656 (K&K 10020/15303), FIGS. 11-50, U.S. Pat. Application Publ. No. 2003-0072964 (Thompson et al.), paragraphs 7-132; and FIGS. 1-8; U.S. Pat. Application Publ. No. 2002-0182441 (Lamansky et al.), paragraphs 13-165, including FIGS. 1-9(g); U.S. Pat. No. 6,420,057 B1 (Ueda et al.), col. 1, line 57, through col. 88, line 17, including each compound I-1 through XXIV-12; U.S. Pat. No. 6,383,666 B1 (Kim et al.), col. 2, line 9, through col. 21, line 67; U.S. Pat. Application Publ. No. 2001-0015432 A1 (Igarashi et al.), paragraphs 2-57, including compounds (1-1) through (1-30); U.S. Pat. Application Publ. No. 2001-0019782 A1 (Igarashi et al.), paragraphs 13- 126, including compounds (1-1) through (1-70), and (2-1) through (2-20); U.S. Pat. Application Publ. No. 2002-0024293 (Igarashi et al.), paragraphs 7-95, including general formulas K-I through K-VI, and example compounds (K-1) through (K-25); U.S. Pat. Application Publ. No. 2002-0048689 A1 (Igarashi et al.), paragraphs 5-134, including compounds 1-81, and example compounds (1-1) through (1-81); U.S. Pat. Application Publ. No. 2002-0063516 (Tsuboyama et al.), paragraphs 31-161, including each compound 1-16; U.S. Pat. Application Publ. No. 2003-0068536 (Tsuboyama et al.), paragraphs 31-168, including each compound in Tables 1-17, corresponds to EP-1-239-526-A2; U.S. Pat. Application Publ. No. 2003-0091862 (Tokito et al.), paragraphs 10-190, including each compound in Tables 1-17, corresponds to EP-1-239-526-A2; U.S. Pat. Application Publ. No. 2003-0096138 (Lecloux et al.), paragraphs 8-124, including FIGS. 1-5; U.S. Pat. Application Publ. No. 2002-0190250 (Grushin et al.), paragraphs 9-191; U.S. Pat. Application Publ. No. 2002-0121638 (Grushin et al.), paragraphs 8-125; U.S. Pat. Application Publ. No. 2003-0068526 (Kamatani et al.), paragraphs 33-572, including each compound in Tables 1-23; U.S. Pat. Application Publ. No. 2003-0141809 (Furugori et al.), paragraphs 29-207; U.S. Pat. Application Publ. No. 2003-0162299 A1 (Hsieh et al.), paragraphs 8-42; WO 03/084972, (Stossel et al.), Examples 1-33; WO 02/02714 A2 (Petrov et al.), pages 2-30, including each compound in Tables 1-5; EP 1-191-613 A1 (Takiguchi et al.), paragraphs 26-87, including each compound in Tables 1-8, (corresponding to U.S. Pat. Application Publ. No. 2002-0064681); and EP 1-191-614 A2 (Tsuboyama et al.), paragraphs 25-86, including each compound in Tables 1-7; which are incorporated herein by reference in their entirety.

    
    


Carbene ligands may be synthesized using methods known in the art, such as those disclosed in Cattoën, et al., J. Am. Chem. Soc., 2004, 126; 1342-1343; Chiu-Yuen Wong, et al, Organometallics 2004, 23, 2263-2272; Klapars, et al, J. Am. Chem. Soc., 2001, 123; 7727-7729; Bourissou et al. Chem Rev. 2000, 100, 39-91; Siu-Wai Lai, et al, Organometallics 1999, 18, 3327-3336; Wen-Mei Xue et al., Organometallics 1998, 17, 1622-1630; Wang & Lin, Organometallics 1998, 17, 972-975; Cardin, et al., Chem Rev. 1972, 5, 545-574; and other references discussed herein.
In one embodiment, a phosphorescent emissive compound having the following formula is provided:




wherein Z1 and Z2 may be a carbon containing moiety, an amine containing moiety, oxygen containing moiety, a phosphine containing moiety, and a sulfur containing moiety.

In another embodiment, the compound has the structure:




in which the ligands have the structure:





in which

    M is a metal;
    the dotted lines represent optional double bonds;
    each Z1, A, and A′ is independently selected from C, N, O, P, or S; R1, R2, and R3 are independently selected from H, alkyl, aryl or heteroaryl; and additionally or alternatively, one or more of R1 and R2 and R2 and R3 together form independently a 5 or 6-member cyclic group, wherein said cyclic group is cycloalkyl, cycloheteroalkyl, aryl or heteroaryl; and wherein said cyclic group is optionally substituted by one or more substituents J; each substituent J is independently selected from the group consisting of R′, O—R′, N(R′)2, SR′, C(O)R′, C(O)OR′, C(O)NR′2, CN, NO2, SO2, SOR′, or SO3R′, and additionally, or alternatively, two J groups on adjacent ring atoms form a fused 5- or 6-membered aromatic group; each R′ is independently selected from H, alkyl, alkenyl, alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl;
    (X—Y) is selected from a photoactive ligand or an ancillary ligand,
    a is 0, 1, or 2.
    m is a value from 1 to the maximum number of ligands that may be attached to the metal;
    m+n is the maximum number of ligands that may be attached to metal M.


The term “halo” or “halogen” as used herein includes fluorine, chlorine, bromine and iodine.
The term “alkyl” as used herein contemplates both straight and branched chain alkyl radicals. Preferred alkyl groups are those containing from one to fifteen carbon atoms and includes methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, and the like. Additionally, the alkyl group may be optionally substituted with one or more substituents selected from halo, CN, CO2R, C(O)R, NR2, cyclic-amino, NO2, and OR.
The term “cycloalkyl” as used herein contemplates cyclic alkyl radicals. Preferred cycloalkyl groups are those containing 3 to 7 carbon atoms and includes cyclopropyl, cyclopentyl, cyclohexyl, and the like. Additionally, the cycloalkyl group may be optionally substituted with one or more substituents selected from halo, CN, CO2R, C(O)R, NR2, cyclic-amino, NO2, and OR.
The term “alkenyl” as used herein contemplates both straight and branched chain alkene radicals. Preferred alkenyl groups are those containing two to fifteen carbon atoms. Additionally, the alkenyl group may be optionally substituted with one or more substituents selected from halo, CN, CO2R, C(O)R, NR2, cyclic-amino, NO2, and OR.
The term “alkynyl” as used herein contemplates both straight and branched chain alkyne radicals. Preferred alkyl groups are those containing two to fifteen carbon atoms. Additionally, the alkynyl group may be optionally substituted with one or more substituents selected from halo, CN, CO2R, C(O)R, NR2, cyclic-amino, NO2, and OR.
The terms “alkylaryl” as used herein contemplates an alkyl group that has as a substituent an aromatic group. Additionally, the alkylaryl group may be optionally substituted on the aryl with one or more substituents selected from halo, CN, CO2R, C(O)R, NR2, cyclic-amino, NO2, and OR.
The term “heterocyclic group” as used herein contemplates non-aromatic cyclic radicals. Preferred heterocyclic groups are those containing 3 or 7 ring atoms which includes at least one hetero atom, and includes cyclic amines such as morpholino, piperdino, pyrrolidino, and the like, and cyclic ethers, such as tetrahydrofuran, tetrahydropyran, and the like.
The term “aryl” or “aromatic group” as used herein contemplates single-ring groups and polycyclic ring systems. The polycyclic rings may have two or more rings in which two carbons are common by two adjoining rings (the rings are “fused”) wherein at least one of the rings is aromatic, e.g., the other rings can be cycloalkyls, cycloalkenyls, aryl, heterocycles and/or heteroaryls.
The term “heteroaryl” as used herein contemplates single-ring hetero-aromatic groups that may include from one to three heteroatoms, for example, pyrrole, furan, thiophene, imidazole, oxazole, thiazole, triazole, pyrazole, pyridine, pyrazine and pyrimidine, and the like. The term heteroaryl also includes polycyclic hetero-aromatic systems having two or more rings in which two atoms are common to two adjoining rings (the rings are “fused”) wherein at least one of the rings is a heteroaryl, e.g., the other rings can be cycloalkyls, cycloalkenyls, aryl, heterocycles and/or heteroaryls.
All value ranges, for example those given for n and m, are inclusive over the entire range. Thus, for example, a range between 0-4 would include the values 0, 1, 2, 3 and 4.
Embodiments include photoactive carbene ligands. A ligand is referred to as “photoactive” because it is believed that it contributes to the photoactive properties of the emissive material. m represents the number of photoactive ligands. For example, for Ir, m may be 1, 2 or 3. n, the number of “ancillary” ligands of a particular type, may be any integer from zero to one less than the maximum number of ligands that may be attached to the metal. (X—Y) represents an ancillary ligand. These ligands are referred to as “ancillary” because it is believed that they may modify the photoactive properties of the molecule, as opposed to directly contributing to the photoactive properties. The definitions of photoactive and ancillary are intended as non-limiting theories. For example, for Ir, n may be 0, 1 or 2 for bidentate ligands. Ancillary ligands for use in the emissive material may be selected from those known in the art. Non-limiting examples of ancillary ligands may be found in PCT Application Publication WO 02/15645 A1 to Lamansky et al. at pages 89-90, which is incorporated herein by reference.
The metal forming the metal-carbene bond may be selected from a wide range of metals. Preferred metals include main group metals, 1st row transition metals, 2nd row transition metals, 3rd row transition metals, and lanthanides. Although one skilled in the art typically expects room temperature phosphorescence only from metal atoms that exert a strong heavy atom effect, phosphorescent emission has been observed in Kunkley, et al. J. Organometallic Chem. 2003, 684, 113-116 for a compound with a Nickel (Ni) metal, which is typically not expected to exert a strong heavy atom effect. Thus, embodiments also include first row transition metal, such as Ni, and other metals that do not normally exert a strong heavy atom effect but exhibits phosphorescent emission when coordinated to one or more carbene ligands. More preferred metals include 3rd row transition metals. The following are also preferred metals: Ir, Pt, Pd, Rh, Re, Ru, Os, Tl, Pb, Bi, In, Sn, Sb, Te, Au, and Ag. Most preferably, the metal is Iridium.
The most preferred embodiments are N-heterocyclic carbenes, which Bourissou has also reported as having “remarkable stability” as free compounds in Bourissou et al. Chem Rev. 2000, 100, 39-91.
In one embodiment, the metal-carbene compound has the structure




and a ligand with the structure





in which R4 is either an aromatic or an axnine group; and R3 and R4 together form independently a 5 or 6-member cyclic group, which may be cycloalkyl, cycloheteroalkyl, aryl or heteroaryl, and which may optionally be substituted by one or more substituents J.

In other embodiments, the metal-carbene compound may have one of the following structures




in which the ligand has the corresponding structure selected from:





in which R5 and R6 may be alkyl, alkenyl, alkynyl, aralkyl, R′, O—R′, N(R′)2, SR′, C(O)R′, C(O)OR′, C(O)NR′2, CN, CF3, NO2, SO2, SOR′, SO3R′, halo, aryl, and heteroaryl; and each R′ is independently selected from H, alkyl, alkenyl, alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl; and additionally or alternatively, one or more of R1 and R2, R2 and R3, R3 and R5 and R5 and R6 together form independently a 5 or 6-member cyclic group, wherein said cyclic group is cycloalkyl, cycloheteroalkyl, aryl or heteroaryl; and wherein said cyclic group is optionally substituted by one or more substituents J.

In another embodiment the metal carbene compound has the structure:




and the carbene ligand has the structure





in which R8, R9, R10, and R11 may be alkyl, alkenyl, alkynyl, aralkyl, R′, O—R′, N(R′)2, SR′, C(O)R′, C(O)OR′, C(O)NR′2, CN, CF3, NO2, SO2, SOR′, SO3R′, aryl, and heteroaryl; each R′ is independently selected from H, alkyl, alkenyl, alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl; and additionally or alternatively, one or more of R1 and R2, R2 and R8, R8 and R10, and R6 and R10 together form independently a 5 or 6-member cyclic group, wherein said cyclic group is cycloalkyl, cycloheteroalkyl, aryl or heteroaryl; and wherein said cyclic group is optionally substituted by one or more substituents J.

In another embodiment, the carbene-metal compound may have one of the structures below:




in which the ligand has the structure selected from





in which each R12 may be an alkyl, alkenyl, alkynyl, aralkyl, R′, O—R′, N(R′)2, SR′, C(O)R′, C(O)OR′, C(O)NR′2, CN, CF3, NO2, SO2, SOR′, SO3R′, halo, aryl, and heteroaryl; each R′ is independently selected from H, alkyl, alkenyl, alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl; or alternatively, two R12 groups on adjacent ring atoms may form a fused 5- or 6-membered cyclic group, wherein said cyclic group is cycloalkyl, cycloheteroalkyl, aryl or heteroaryl; and wherein said cyclic group is optionally substituted by one or more substituents J; and d is 0, 1, 2, 3 , or 4.

Another embodiment has a metal-carbene structure:




with a ligand having the structure





in which each R13 may be an alkyl, alkenyl, alkynyl, aralkyl, R′, O—R′, N(R′)2, SR′, C(O)R′, C(O)OR′, C(O)NR′2, CN, CF3, NO2, SO2, SOR′, SO3R′, halo, aryl, and heteroaryl; each R′ is independently selected from H, alkyl, alkenyl, alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl; or alternatively, two R13 groups on adjacent ring atoms may form a fused 5- or 6-membered cyclic group, in which the cyclic group is cycloalkyl, cycloheteroalkyl, aryl or heteroaryl; and which is optionally substituted by one or more substituents J; and c may be 0, 1, 2, or 3.

Preferred embodiments include metal-carbene compounds having the structure selected from:




with corresponding ligands having the structures selected from





in which Z2 and Z3 may be O, S, N—R6, or P—R6 and ring B is independently an aromatic cyclic, heterocyclic, fused cyclic, or fused heterocyclic ring with at least one carbon atom coordinated to metal M, in which ring B may be optionally substituted with one or more substituents R14; and ring D is independently a cyclic, heterocyclic, fused cyclic, or fused heterocyclic ring with at least one carbon atom coordinated to metal M, in which ring B may be optionally substituted with one or more substituents R15; and R14 and R15 are independently selected from alkyl, alkenyl, alkynyl, aralkyl, R′, O—R′, N(R′)2, SR′, C(O)R′, C(O)OR′, C(O)NR′2, CN, CF3, NO2, SO2, SOR′, SO3R′, halo, aryl, and heteroaryl; each R′ is independently selected from H, alkyl, alkenyl, alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl; or alternatively, two R14 groups on adjacent ring atoms and R15 groups on adjacent ring atoms form a fused 5- or 6-membered cyclic group, in which the cyclic group is cycloalkyl, cycloheteroalkyl, aryl or heteroaryl; and which is optionally substituted by one or more substituents J; b may be 0, 1, 2, 3, or 4; and e may be 0, 1, 2, or 3.

In one embodiment the metal-carbene compound has the structure:




in which the ligand has the structure





Preferably, the compound has the structure:




and the ligand has the structure:





More preferably the metal-carbene has a structure selected from:







Another preferred embodiment has the structure:




in which the ligand has the structure





in which R6 is an alkyl or aryl group. In a most preferred embodiment, the metal is Ir. Preferably, m is 3 and n is 0. In one embodiment, R6 is methyl. In another embodiment m is 2 and n is one. The ancillary ligand X—Y may be have one of the following structures:





Other preferred ancillary ligands are acetylacetonate, picolinate, and their derivatives.
Other preferred embodiments have the following general structures:







More preferred embodiments have the following structures:














and more preferred ligands have the following corresponding structures











Other embodiments may have the general structure:




and the ligand may have the corresponding structure





Preferably, the metal-carbene compound has the structure:





and the carbene ligand has the structure





Other preferred embodiments include:







in which the ligands have the structure:





It is understood that the various embodiments described herein are by way of example only, and are not intended to limit the scope of the invention. For example, many of the materials and structures described herein may be substituted with other materials and structures without deviating from the spirit of the invention. It is understood that various theories as to why the invention works are not intended to be limiting. For example, theories relating to charge transfer are not intended to be limiting.
MATERIAL DEFINITIONS
As used herein, abbreviations refer to materials as follows:













CBP:
4,4′-N,N-dicarbazole-biphenyl


m-MTDATA
4,4′,4′′-tris(3-methylphenylphenly-



amino)triphenylamine


Alq3:
8-tris-hydroxyquinoline aluminum


Bphen:
4,7-diphenyl-1,10-phenanthroline


n-BPhen:
n-doped BPhen (doped with lithium)


F4-TCNQ:
tetrafluoro-tetracyano-quinodimethane


p-MTDATA:
p-doped m-MTDATA (doped with



F4-TCNQ)


Ir(ppy)3:
tris(2-phenylpyridine)-iridium


Ir(ppz)3:
tris(1-phenylpyrazoloto,N,C(2′)iridi-



um(III)


BCP:
2,9-dimethyl-4,7-diphenyl-1,10-



phenanthroline


TAZ:
3-phenyl-4-(1′-naphthyl)-5-phenyl-



1,2,4-triazole


CuPc:
copper phthalocyanine.


ITO:
indium tin oxide


NPD:
N,N′-diphenyl-N-N′-di(1-naphthyl)-



benzidine


TPD:
N,N′-diphenyl-N-N′-di(3-toly)-benzidine


BAlq:
aluminum(III)bis(2-methyl-8-hydroxy-



quinolinato)4-phenylphenolate


mCP:
1,3-N,N-dicarbazole-benzene


DCM:
4-(dicyanoethylene)-6-(4-dimethyl-



aminostyryl-2-methyl)-4H-pyran


DMQA:
N,N′-dimethylquinacridone


PEDOT:PSS:
an aqueous dispersion of poly(3,4-



ethylenedioxythiophene) with



polystyrenesulfonate (PSS)


1-Ph-3-Me-imid
1-phenyl-3-methyl-imidazolin-2-



ylidene-C,C2′


1-Ph-3-Me-benzimid
fac-iridium(III)tris(1-phenyl-3-methyl-



benzimidazolin-2-ylidene-C,C2′)


mer-(F2ppz)2Ir(1-Ph-3-Me-imid)
mer-iridium(III)bis[(2-(4′,6′-difluoro-



phenyl)-2-pyrazolinato-N,C2′)](1-



phenyl-3-methyl-imidazolin-2-ylidene-



C,C2′)


mer-(2-(tpy)2Ir(1-Ph-3-Me-imid)
mer-iridium(III)bis[(2-(4′-



methylphenyl)-2-pyridinato-N,C2)](1-



phenyl-3-methyl-imidazolin-2-ylidene-



C,C2


fac-(2-(tpy)2Ir(1-Ph-3-Me-imid)
fac-iridium(III)bis[(2-(4′-methylphenyl)-



2-pyridinato-N,C2′)](1-phenyl-3-methyl-



imidazolin-2-ylidene-C,C2′)


[(1-Ph-3-Me-imid)2IrCl]2
Iridium(III)bis(1-phenyl-3-methyl-



imidazolin-2-ylidene-C,C2′) chloride


(1-Ph-3-Me-imid)2Ir(t-Bu-bpy)+
Iridium(III)bis[(1-phenyl-3-methyl-



imidazolin-2-ylidene-C,C2′)](4,4′-di-tert-



butyl-(2,2′)bipyridinyl)


mer-Ir(1-Ph-3-Me-imid)3
mer-iridium(III)tris(1-phenyl-3-methyl-



imidazolin-2-ylidene-CC2′)


(Ir-Fl-Me-imid)3
tris(1-(2′-(9′,9′-dimethyl)fluorenyl)-3-



methyl-imidazolin-2-ylidene-C,C3′)



iridium(III)









EXPERIMENTAL
Specific representative embodiments of the invention will now be described, including how such embodiments may be made. It is understood that the specific methods, materials, conditions, process parameters, apparatus and the like do not necessarily limit the scope of the invention.
Synthesis of Imidazolate Carbene Precursors
1-Phenylimidazole was purchased from Aldrich. All other aryl imidazoles were prepared by a modified Ullmann coupling reaction between imidazole or benzimidazole and the appropriate aryl iodide in anhydrous N,N-dimethylformamide using a CuI/1,10-phenanthroline catalyst and Cs2CO3 base, as described in Klapars, et al, J. Am. Chem. Soc., 2001, 123; 7727-7729. The carbene precursor imidazolates were prepared by methylating the corresponding imidazoles with excess methyl iodide in toluene.
Example 1
Synthesis of 1-phenyl-3-methylimidazolate iodide
1-phenyl-3-methylimidazolate iodide was synthesized using the modified Ullmann coupling reaction described above. 1H NMR (250MHz, CDCl3), ppm: 10.28 (s, 1H), 7.77-7.70 (m, 4H), 7.56-7.46 (m, 3H), 4.21 (s, 3H).
Example 2
Synthesis of 1-Phenyl-3-methyl-benzimidazolate iodide
In the dark, an oven-dried 50 ml round-bottomed flask containing a stir bar was charged with CuI (0.171 g, 0.1 eq.), benzimidazole (1.273 g, 1.2 eq.), and cesium carbonate (6.138 g, 2.1 eq.) respectively. The round-bottomed flask with the contents was sealed with septa and degassed with argon for 15 minutes. Iodobenzene (1 ml, 1 eq.), 1,10-Phenanthroline (0.323 g, 0.2 eq.), and dimethylformamide (25 ml) were then successively added into the round-bottomed flask under a continuous flow of argon. The reaction mixture was degassed with argon for 30 minutes. The reaction was stirred with heating via an oil bath at 110° C. for 24 hours in the dark under nitrogen. The reaction mixture was cooled to ambient temperature and concentrated in vacuo. 10 ml of ethyl acetate was added into the concentrated reaction mixture. It was then filtered and washed with 30 ml of ethyl acetate. The filtrate was concentrated under vacuo to give the crude product. The crude product was purified by column chromatography on silica gel (40% ethyl acetate: 60% hexane as the eluent) providing 0.780 g of 1-Phenyl benzoimidazole (45% yield) as yellow liquid.
Methyl iodide (0.550 ml, 2.2 eq.) was syringed into a 25 ml round-bottomed flask charged with 1-phenyl benzoimidazole (0.780 g, 1 eq.) and toluene (15 ml). The reaction was stirred and heated at 30° C. for 24 hours. The white precipitate was filtered and washed with 20 ml of toluene. The white precipitate was air-dried and weighed to give 0.725 g of 1-phenyl-3-methyl-benzimidizolate iodide (54% yield).
Synthesis of Iridium Imidazole Carbene Complexes
Example 3
Synthesis of mer-iridium(III) bis[(2-(4′,6′-difluorophenyl)-2-pyrazolinato-N,C2′)](1-phenyl-3-methyl-imidazolin-2-ylidene-C,C2′)
A 25 ml round-bottomed flask was charged with 0.014 g of silver(I) oxide, 0.030 g of 1-phenyl-3-methyl-imidazolate iodide, 0.062 g of [(F2ppz)2IrCl]2, and 15 ml of 1,2-dichloroethane. The reaction was stirred and heated with an oil bath at 77° C. for 15 hours in the dark under nitrogen while protected from light with aluminum foil. The reaction mixture was cooled to ambient temperature and concentrated under reduced pressure. Filtration through Celite using dichloromethane as the eluent was performed to remove the silver(I) salts. A light yellow solution was obtained and addition of methanol gave 0.025 g (30% yield) of iridium complex as a colorless solid.
1H NMR (500MHz, CDCl3), ppm: 8.24 (d, 1H, J=2.8 Hz), 8.16 (d, 1H, J=2.8 Hz), 7.43 (d, 1H, J=1.9 Hz), 7.15 (d, 1H, J=7.5 Hz), 6.96 (ddd, 1H, J=7.5, 7.0, 1.9 Hz), 6.93 (dd, 1H, J=7.0, 1.9 Hz), 6.82 (m, 2H), 6.78 (d, 1H, J=1.9 Hz), 6.47 (ddd, 1H, J=11.7, 8.4, 2.3 Hz), 6.43 (ddd, 1H, J=11.7, 8.4, 2.3 Hz), 6.29 (t, 1H, J=2.3 Hz), 6.28 (t, 1H, J=2.3 Hz), 6.14 (dd, 1H, J=7.5, 2.3 Hz), 5.85 (dd, 1H, J=8.0, 2.3 Hz), 3.29 (s, 3H).
FIG. 3 shows the 1H NMR spectra of mer-(F2ppz)2Ir(1-Ph-3-Me-imid) in CDCl3.
Example 4
Synthesis of mer-iridium(III) bis[(2-(4′-methylphenyl)-2-pyridinato-N,C2′)](1-phenyl-3-methyl-imidazolin-2-ylidene-C,C2′)
A 50 ml round-bottomed flask was charged with 0.103 g of silver(I) oxide, 0.118 g of 1-phenyl-3-methyl-imidazolate iodide, 0.168 g of [(tpy)2IrCl]2, and 25 ml of 1,2-dichloroethane. The reaction was stirred and heated with an oil bath at 77° C. for 15 hours in the dark under nitrogen while protected from light with aluminum foil. The reaction mixture was cooled to ambient temperature and concentrated under reduced pressure. Filtration through Celite using dichloromethane as the eluent was performed to remove the silver(I) salts. A yellow solution was obtained and further purified by flash column chromatography on silica gel using dichloromethane as the eluent that was reduced in volume to ca. 2 ml. Addition of methanol gave 0.121 g (59% yield) of iridium complex as a bright yellow solid.
FIG. 4 shows the 1H NMR spectra of mer-(tpy)2Ir(1-Ph-3-Me-imid) in CDCl3. FIG. 6 shows the plot of current (μA) vs. voltage (V) of a mer-(tpy)2Ir(1-Ph-3-Me-imid) compound with ferrocene as an internal reference. A solvent of DMF with 0.1M Bu4N+PF6− is used. FIG. 9 shows the emission spectra of mer-(tpy)2Ir(1-Ph-3-Me-imid) in 2-MeTHF at room temperature and at 77K. The compound exhibits lifetimes of 1.7 μs at room temperature and 3.3 μs at 77K.
Example 5
Synthesis of fac-iridium(III) bis[(2-(4′-methylphenyl)-2-pyridinato-N,C2′)](1-phenyl-3-methyl-imidazolin-2-ylidene-C,C2′)
A 200 ml quartz flask was charged with 0.0.059 g of mer-(tpy)2Ir(1-Ph-3-Me-imid) and 50 ml of acetonitrile and sparged with nitrogen for five minutes. The mixture was photolyzed for 63 hours using 254 nm light. After photolysis the solvent was removed under reduced pressure and the yellow solid was taken up in 2 ml dichloromethane. Addition of methanol gave 0.045 g (75% yield) of iridium complex as a bright yellow solid that was collected by centrifuge.
FIG. 5 shows the 1H NMR spectra of fac-(tpy)2Ir(1-Ph-3-Me-imid) in CDCl3. FIG. 7 shows the plot of current (μA) vs. voltage (V) of a fac-(tpy)2Ir(1-Ph-3-Me-imid) compound with ferrocene as an internal reference. A solvent of DMF with 0.1M Bu4N+PF6− is used. FIG. 8 shows the absorption spectra of fac-(tpy)2Ir(1-Ph-3-Me-imid) and mer-(tpy)2Ir(1-Ph-3-Me-imid) in CH2Cl2. FIG. 10 shows the emission spectra of fac-(tpy)2Ir(1-Ph-3-Me-imid) in 2-MeTHF at room temperature and at 77K. The compound exhibits lifetimes of 1.7 μs at room temperature and 3.3 μs at 77K.
Example 6
Synthesis of Iridium(III) bis(1-phenyl-3-methyl-imidazolin-2-ylidene-C,C2′) chloride dimer
A 100 ml round-bottomed flask was charged with 0.428 g of silver(I) oxide, 0.946 g of 1-phenyl-3-methyl-imidazolate iodide, 0.301 g of iridium trichloride hydrate, and 60 ml of 2-ethoxyethanol. The reaction was stirred and heated with an oil bath at 120° C. for 15 hours under nitrogen while protected from light with aluminum foil. The reaction mixture was cooled to ambient temperature and the solvent was removed under reduced pressure. The black mixture was extracted with ca. 20 ml dichloromethane and the extract was reduced to ca. 2 ml volume. Addition of methanol gave 0.0160 g (30% yield) of the iridium dimer complex as an off-white solid.
FIG. 11 shows the 1H NMR spectra of [(1-Ph-3-Me-imid)2IrCl]2 in CDCl3.
Example 7
Synthesis of mer-iridium(III) tris(1-phenyl-3-methyl-imidazolin-2-ylidene-C,C2′)
A 50 ml round-bottomed flask was charged with 0.076 g of silver(I) oxide, 0.109 g of 1-phenyl-3-methyl-imidazolate iodide, 0.029 g of iridium trichloride hydrate, and 20 ml of 2-ethoxyethanol. The reaction was stirred and heated with an oil bath at 120° C. for 15 hours under nitrogen while protected from light with aluminum foil. The reaction mixture was cooled to ambient temperature and concentrated under reduced pressure. Filtration through Celite using dichloromethane as the eluent was performed to remove the silver(I) salts. A white solid was obtained after removing the solvent in vacuo and was washed with methanol to give 0.016 g (24% yield) of meridional tris-iridium complex as a white solid.
FIG. 15 shows the 1H NMR spectra of mer-Ir(1-Ph-3-Me-imid)3 in CDCl3. FIG. 16 shows the 13C NMR spectra of mer-Ir(1-Ph-3-Me-imid)3 in CDCl3. FIG. 17 shows the plot of current (μA) vs. voltage (V) of a mer-Ir(1-Ph-3-Me-imid)3 compound with ferrocene as an internal reference. A solvent of DMF with 0.1M Bu4N+PF6− is used. FIG. 18 shows the emission spectra of mer-Ir(1-Ph-3-Me-imid)3 in 2-MeTHF at room temperature and at 77K.
Example 8
Synthesis of fac-iridium(III) tris(1-phenyl-3-methyl-imidazolin-2-ylidene-C,C2′)
A 50 ml round-bottomed flask was charged with 0.278 g of silver(I) oxide, 0.080 g of 1-phenyl-3-methyl-imidazolate iodide, 0.108 g of [(1-Ph-3-Me-imid)2IrCl]2, and 25 ml of 1,2-dichloroethane. The reaction was stirred and heated with an oil bath at 77° C. for 15 hours under nitrogen while protected from light with aluminum foil. The reaction mixture was cooled to ambient temperature and concentrated under reduced pressure. Filtration through Celite using dichloromethane as the eluent was performed to remove the silver(I) salts. A light brown solution was obtained and further purified by flash column chromatography on silica gel using dichloromethane as the eluent and was then reduced in volume to ca. 2 ml. Addition of methanol gave 0.010 g (8% yield) of iridium complex as a colorless solid.
FIG. 19 shows the 1H NMR spectra of fac-Ir(1-Ph-3-Me-imid)3 in CDCl3. FIG. 20 shows the absorption spectra of fac-Ir(1-Ph-3-Me-imid)3 in CH2Cl2. FIG. 21 shows the emission spectra of fac-Ir(1-Ph-3-Me-imid)3 in 2-MeTHF at room temperature and at 77K. The compound exhibits lifetimes of 0.50 μs at room temperature and 6.8 μs at 77K.
Example 9
Synthesis of fac-iridium(III) tris(1-phenyl-3-methyl-benzimidazolin-2-ylidene-C,C2′)
A 25 ml round-bottomed flask was charged with 0.165 g of silver(I) oxide, 0.200 g of 1-phenyl-3-methyl-benzimidazolate iodide, 0.0592 g of iridium trichloride hydrate, and 15 ml of 2-ethoxyethanol. The reaction was stirred and heated with an oil bath at 120° C. for 24 hours under nitrogen while protected from light with aluminum foil. The reaction mixture was cooled to ambient temperature and concentrated under reduced pressure. Flash column chromatography on Celite using dichloromethane as the eluent was performed to remove the silver(I) salts. A brown oil was obtained and further purified by flash column chromatography on silica gel using dichloromethane as the eluent to give 0.050 g of facial tris-iridium complex (33% yield) as an off-white solid.
FIG. 22 shows the 1H NMR spectra of 1-Ph-3-Me-benzimid in CDCl3. FIG. 23 shows the 1H NMR spectra of fac-Ir(1-Ph-3-Me-benzimid)3 in CDCl3. FIG. 24 shows the plot of current (mA) vs. voltage (V) of a fac-Ir(1-Ph-3-Me-benzimid)3 compound with ferrocene as an internal reference. A solvent of anhydrous DMF is used. FIG. 25 shows the emission spectra of fac-Ir(1-Ph-3-Me-benzimid)3 in 2-MeTHF at room temperature and at 77K. The compound emits a spectrum at CIE 0.17, 0.04. The lifetime measurements of an Ir(1-Ph-3-Me-benzimid)3 compound is shown on Table I.









TABLE I





Temperature
Peak wavelength
Lifetime, t


















Room temperature
402 nm
0.32
μs


Room temperature
420 nm
0.29
μs


77 K
400 nm
2.6
μs


77 K
420 nm
2.7
μs









Example 9
Synthesis of iridium(III) bis(1-phenyl-3-methyl-imidazolin-2-ylidene-C,C2′) (4,4′-di-tert-butylbipyidyl)hexafluorophosphate
A 25 ml round-bottomed flask was charged with 0.010 g of [(1-Ph-3-Me-imid)2IrCl]2, 0.005 g of 4′4′-di-tert-butyl-bipyridine and 15 ml of dichloromethane. The reaction was stirred at room temperature for 16 hours. The solvent was removed under reduced pressure and the resultant yellow solid was dissolved in ca. 2 ml methanol. Addition of an aqueous ammonium hexafluorophosphate solution produced a yellow precipitate. The precipitate was collected by filtration, washed with water and dried. Chromatography on silica addition of hexanes gave 0.015 g (82% yield) of iridium complex as an orange solid.
FIG. 12 shows the 1H NMR spectra of (1-Ph-3-Me-imid)2Ir(t-Bu-bpy)+ in CDCl3. FIG. 13 shows the absorption spectra of (1-Ph-3-Me-imid)2Ir(t-Bu-bpy)+ in CH2Cl2. FIG. 14 shows the emission spectra of (1-Ph-3-Me-imid)2Ir(t-Bu-bpy)+ in 2-MeTHF at 77K and (1-Ph-3-Me-imid)2Ir(t-Bu-bpy)+ in CH2Cl2 at room temperature. The compound exhibits lifetimes of 0.70 μs at room temperature and 6.0 μs at 77K.
While the present invention is described with respect to particular examples and preferred embodiments, it is understood that the present invention is not limited to these examples and embodiments. The present invention as claimed therefore includes variations from the particular examples and preferred embodiments described herein, as will be apparent to one of skill in the art.

## Claims

1. A compound selected from the group consisting of:



wherein
Z3 is selected from the group consisting of O, S, N—R6, or P—R6, wherein R6 is independently selected from the group consisting of alkyl, alkenyl, alkynyl, aralkyl, O—R′, N(R′)2, SR′, C(O)R′, C(O)OR′, C(O)NR′2, CN, CF3, NO2, SO2, SOR′, SO3R′, halo, and heteroaryl; each R′ is independently selected from H, alkyl, alkenyl, alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl; and
A is independently selected from C, N, O, P, or S;
(X—Y) is a bidentate photoactive ligand or a bidentate ancillary ligand;
ring B is independently an aromatic cyclic, heterocyclic, fused cyclic, or fused heterocyclic ring, wherein ring B can be optionally substituted with one or more substituents R14; and
ring D is independently a cyclic, heterocyclic, fused cyclic, or fused heterocyclic ring with at least one carbon atom coordinated to metal M, wherein ring D can be optionally substituted with one or more substituents R15; and
R14 and R15 are independently selected from alkyl, alkenyl, alkynyl, aralkyl, R′, O—R′, N(R′)2, SR′, C(O)R′, C(O)OR′, C(O)NR′2, CN, CF3, NO2, SO2, SOR′, SO3R′, halo, aryl, and heteroaryl; each R′ is independently selected from H, alkyl, alkenyl, alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl; or
alternatively, two R14 groups on adjacent ring atoms and R15 groups on adjacent ring atoms form a fused 5- or 6-membered cyclic group, wherein said cyclic group is cycloalkyl, cycloheteroalkyl, aryl or heteroaryl; and wherein said cyclic group is optionally substituted by one or more substituents J;
b is 0, 1, 2, 3, or 4;
e is 0, 1, 2, or 3;
m has a value from 1 to the maximum number of ligands that may be attached to the metal; and m+n is the maximum number of ligands that may be attached to metal M.

2. The compound of claim 1, wherein the compound is selected from the group consisting of:

3. The compound of claim 2, wherein the compound has the structure:

4. The compound of claim 2, wherein the compound has the structure:




R8 and R10 are independently selected from the group consisting of H, alkyl, alkenyl, alkynyl, aralkyl, R′, O—R′, N(R′)2, SR′, C(O)R′, C(O)OR′, C(O)NR′2, CN, CF3, NO2, SO2, SOR′, SO3R′, halo, aryl, and heteroaryl; each R′ is independently selected from H, alkyl, alkenyl, alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl;
and additionally or alternatively, R8 and R10 together form a 5 or 6-member cyclic group,
wherein said cyclic group is cycloalkyl, cycloheteroalkyl, aryl, or heteroaryl; and wherein
said cyclic group is optionally substituted by one or more substituents J.

5. The compound of claim 4, wherein the compound is selected from the group consisting of:

6. The compound of claim 5, wherein the compound has the structure:



wherein R6 is an alkyl.

7. The compound of claim 6, wherein M is selected from a group consisting of main group metals, 1st row transition metals, 2nd row transition metals, 3rd row transition metals, and lanthanides.

8. The compound of claim 7, wherein M is selected from the group consisting of Ir, Pt, Pd, Rh, Re, Ru, Os, Tl, Pb, Bi, In, Sn, Sb, Te, Au, and Ag.

9. The compound of claim 8, wherein M is Ir.

10. The compound of claim 9, wherein m is 3 and n is 0.

11. The compound of claim 10, wherein R6 is methyl.

12. The compound of claim 9, wherein m is 2.

13. The compound of claim 12, wherein X—Y is selected from the group consisting of:




acetylacetonate, and picolinate.

14. The compound of claim 5, wherein the compound is selected from the group consisting of:

15. The compound of claim 14, wherein M is selected from a group consisting of main group metals, 1st row transition metals, 2nd row transition metals, 3rd row transition metals, and lanthanides.

16. The compound of claim 15, wherein M is selected from the group consisting of Ir, Pt, Pd, Rh, Re, Ru, Os, Tl, Pb, Bi, In, Sn, Sb, Te, Au, and Ag.

17. The compound of claim 16, wherein M is Ir.

18. The compound of claim 17, wherein m is 3 and n is 0.

19. The compound of claim 17, wherein m is 2.

20. The compound of claim 5, wherein the compound has the structure



wherein R6 is an alkyl group.

21. The compound of claim 20, wherein M is selected from a group consisting of main group metals, 1st row transition metals, 2nd row transition metals, 3rd row transition metals, and lanthanides.

22. The compound of claim 21, wherein M is selected from the group consisting of Ir, Pt, Pd, Rh, Re, Ru, Os, Tl, Pb, Bi, In, Sn, Sb, Te, Au, and Ag.

23. The compound of claim 22, wherein M is Ir.

24. The compound of claim 23, wherein m is 3 and n is 0.

25. The compound of claim 24, wherein R6 is methyl.

26. The compound of claim 23, wherein m is 2.

27. The compound of claim 2, wherein the compound is selected from the group consisting of:



wherein ring B is an aromatic cyclic, heterocyclic, fused cyclic, or fused heterocyclic ring with at least one carbon atom coordinated to metal M; and
R8 and R10 are independently selected from the group consisting of H, alkyl, alkenyl, alkynyl, aralkyl, R′, O—R′, N(R′)2, SR′, C(O)R′, C(O)OR′, C(O)NR′2, CN, CF3, SO2, SOR′, SO3R′, halo, aryl, and heteroaryl; each R′ is independently selected from H, alkyl, alkenyl, alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl;
each R14 is independently selected from alkyl, alkenyl, alkynyl, aralkyl, R′, O—R′, N(R′)2, SR′, C(O)R′, C(O)OR′, C(O)NR′2, CN, CF3, NO2, SO2, SOR′, or SO3R′ halo, aryl, and heteroaryl; each R′ is independently selected from H, alkyl, alkenyl, alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl; or
alternatively, two R14 groups on adjacent ring atoms form a fused 5- or 6-membered cyclic group, wherein said cyclic group is cycloalkyl, cycloheteroalkyl, aryl or heteroaryl; and wherein said cyclic group is optionally substituted by one or more substituents J;
b is 0, 1, 2, 3, or 4.

28. The compound of claim 2, wherein the compound is selected from the group consisting of:




wherein R8 and R10 are independently selected from the group consisting of H, alkyl, alkenyl, alkynyl, aralkyl, R′, O—R′, N(R′)2, SR′, C(O)R′, C(O)OR′, C(O)NR′2, CN, CF3, NO2, SO2, SOR′, SO3R′, halo, aryl, and heteroaryl: each R′ is independently selected from H, alkyl, alkenyl, alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl.

29. The compound of claim 1, wherein the compound is selected from the group consisting of:







wherein
R8 and R10 are independently selected from the group consisting of H, alkyl, alkenyl, alkynyl, aralkyl, R′, O—R′, N(R′)2, SR′, C(O)R′, C(O)R′, C(O)NR′2, CN, CF3, NO2, SO2, SOR′, SO3R′, halo, aryl, and heteroaryl; each R′ is independently selected from H, alkyl, alkenyl, alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl;
and additionally or alternatively, R8 and R10 together form a 5 or 6-member cyclic group, wherein said cyclic group is cycloalkyl, cycloheteroalkyl, aryl, or heteroaryl; and wherein said cyclic group is optionally substituted by one or more substituents J:
each R12 is independently selected from alkyl, alkenyl, alkynyl, aralkyl, R′, O—R′, N(R′)2, SR′, C(O)R′, C(O)OR′, C(O)NR′2, CN, CF3, NO2, SO2, SOR′, SO3R′, halo, aryl, and heteroaryl; each R′ is independently selected from H, alkyl, alkenyl, alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl; or
alternatively, two R12 groups on adjacent ring atoms form a fused 5- or 6-membered cyclic group, wherein said cyclic group is cycloalkyl, cycloheteroalkyl, aryl or heteroaryl; and wherein said cyclic group is optionally substituted by one or more substituents J; and d is 0, 1, 2, 3, or 4.

30. The compound of claim 1, wherein the compound is selected from the group consisting of:






wherein each R12 is independently selected from alkyl, alkenyl, alkynyl, aralkyl, R′, O—R′, N(R′)2, SR′, C(O)R′, C(O)OR′, C(O)NR′2, CN, CF3, NO2, SO2, SOR′, SO3R′, halo, aryl, and heteroaryl; each R′ is independently selected from H, alkyl, alkenyl, alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl; or
alternatively, two R12 groups on adjacent ring atoms form a fused 5- or 6-membered cyclic group, wherein said cyclic group is cycloalkyl, cycloheteroalkyl, aryl or heteroaryl; and wherein said cyclic group is optionally substituted by one or more substituents J; and d is 0, 1, 2, 3, or 4.

31. The compound of claim 1, wherein M is selected from a group consisting of main group metals, 1st row transition metals, 2nd row transition metals, 3rd row transition metals, and lanthanides.

32. The compound of claim 31, wherein M is selected from the group consisting of Ir, Pt, Pd, Rh, Re, Ru, Os, Tl, Pb, Bi, In, Sn, Sb, Te, Au, and Ag.

33. The compound of claim 32, wherein n is zero and m is the maximum number of ligands that may be attached to metal M.

34. The compound of claim 33, wherein M is Ir.