WO2012088316A1 - 2-alkyl-5-phenyl oxadiazole-carbazole hosts for guest emitters - Google Patents

Abstract

The various inventions and/or their embodiments disclosed herein relate to and include 2-alkyl-5-phenyl-1,3,4-oxadiazole-carbazole ("2-APOC") small molecules having both hole carrying and electron carrying groups bound thereto, and the use of such ambipolar polymers, copolymers, and/or small molecules as host materials for carrying holes, electrons, and/or excitons into contact with guest light emitters, for use in the emissive layers of electronic devices such as organic light emitting diodes.

Description

2-Alkyl-5-Phenyl Oxadiazole-Carbazole Hosts for Guest Emitters

STATEMENT OF GOVERNMENT LICENSE RIGHTS

[0001 ] The inventors received partial funding support through the STC Program of the National Science Foundation under Agreement Number DMR- 020967 and the Office of Naval Research through a MURI program, Contract Award Number 68A- 1060806. The U.S. Government has certain rights in the invention.

TECHNICAL FIELD OF THE INVENTION

[0002] The inventions disclosed and described herein relate generally to small molecule host compounds comprising both oxadizole and carbazole groups that can be used as semiconductors in electronic devices, such as for example to make compositions for the emission layers of organic light emitting diodes

(OLEDs). The small molecule compounds can transport electrons, holes, and/or excitons into contact with the guest emitter in the compositions and/or the emission layers of the OLEDs.

BACKGROUND OF THE INVENTION

[0003] Considerable research has been directed toward the synthesis of organic light-emitting diodes (OLEDs), in view their potential applications in full- color flat panel displays and solid state lighting. Such OLEDs often contain a light emissive layer comprising a luminescent material as a guest, dispersed and/or dissolved in a mixture of host/carrier materials capable of transporting holes, electrons, and/or excitons into contact with the luminescent guest. The luminescent guest is excited by the electrons, holes, and/or energy transfer from the excitons from the host, and then emits light.

[0004] The light emissive layer is typically disposed between an anode and cathode. Single layer OLED devices are known, but typically exhibit very low quantum efficiencies, for a variety of reasons. Efficiency has been dramatically improved in some cases by employing additional layers of semiconductor organic materials in the OLED devices, such as an additional layer comprising an organic semiconductor material optimized for transporting holes from the anode into contact with the emission layer, and/or an additional electron transport layer comprising an organic semiconductor material optimized for carrying electrons from the cathode into contact with the emission layer.

[0005] For example, compounds comprising carbazoles have been utilized as hole transporter and/or electron blocking materials in OLED applications, and in some cases as hole-transporting hosts for luminescent guests. Examples of known carbazole-based ho -carrying materials are shown below.

9-methyl-9H-carbazole

[0006] Similarly, small-molecule 2,5-diaryl oxadiazoles such as those shown below (PBD and OXD-7) are well known as suitable electron carrying materials for use in making electron carrying layers for OLED devices, and have also been used as electron carrying hosts for luminescent guests.

2,5-oxadiazoles

PBD OXD-7

[0007] Upon application of voltage/current across the OLED devices, holes are injected from the anode and through the hole conducting / electron blocking layer, and electrons are injected from the cathode and transported through the electron conducting /hole blocking layer and into the emissive layer. The holes and electrons are thereby ideally confined to the emissive layer, where the holes and electrons can both be transferred directly to the luminescent guest material, or perhaps more typically, the holes and electrons combine on the host material to form both singlet and triplet state excitons in the host materials, and those singlet and triplet excitons can then transfer their energy to form lower energy excited states on the luminescent guest material.

[0008] Identifying host materials that can efficiently perform all these functions is difficult, especially for use with guest materials that emit relatively high photon energy blue light. In order to maximize energy transfer from the host materials to the guest emitters, the energies of both the singlet and triplet states of the hole and/or electron carrying materials in the host should be at least somewhat higher than the energies of the corresponding singlet and triplet states of the guest emitters. To achieve such high energy excited states, the conjugation of the organic host materials must be limited, in order to provide for singlet and triplet energy levels higher than those of the guest emitters. This can be very challenging for OLEDs employing high energy blue guest emitters like FIr6, see for example Fukagawa et al, App. Phys. Lett. 93, 133312 (2008).

[0009] In a few cases, the use of mixtures of hole carrying and electron carrying materials, to form a mixed host material for phosphorescent guests in the emissions layers of multi-layer OLEDs are known. Nevertheless, devices based on such mixtures of hole carrying and electron carrying materials in their emission layers can undergo undesirable phase separations, partial crystallizations, and/or otherwise degrade upon extended OLED device heating, decreasing OLED device efficiency and/or lifetimes over time.

[00010] Small molecules and polymers comprising both hole carrying carbazole and electron carrying 2,5-diphenyl-oxadiazole groups have been reported in the prior art. Guan et al, Chem Commun. 2003, 2708-2709 disclosed a small molecule 2,5-diphenyl-oxadiazole- carbazole compound having the structure below for use in OLEDs. The compounds were used as a direct (but low efficiency) blue fluorescent emitter in OLEDs (no guest triplet emitter was employed).

[0001 1 ] Japanese patent application JP 2008/174661 disclosed similar compounds whose structure is shown below:

[00012] Japanese patent application JP 2002/302251 disclosed the polymerizable styrene monomers whose structure is shown below, and suggested the use of those monomers to make various polymers and copolymers for OLED applications, but again did not suggest the use of the copolymers as hosts for emissive guests for OLED a lications.

[00013] Similar 2,5-diphenyl-oxadiazole- mono-carbazole compound compounds having the structure

were disclosed in EP 1 972 625 (2008). That patent application did suggest the use of the disclosed compounds as hosts for guest triplet emitters, but did not however disclose the actual performance of any OLED devices made from the materials disclosed therein.

[00014] There has also been significant general progress in the art regarding materials that can serve a host for green emitters in OLED applications, some of which can provide External Quantum Efficiencies of 1 5-20%, see for example Yang, Meerholz et al (Adv. Mater. 2006, 1 8, 948-954) which disclosed that an OLED employing an emissive layer comprising a blend of the polymeric carbazole PVK with the PBD small molecule oxadiazole and Ir(mppy)3 guest emitter gave current efficiencies up to 67 cd/A and EQE of 18.8% at 100 cd/m², and 56 cd/A and EQE of 15.7% at 1 000 cd/m². The long term stability of such OLEDs was not however discussed.

[00015] Nevertheless, progress on efficient and long-lived hosts for use with higher photon energy blue emitters has been significantly slower, and the efficiencies of such blue emitting OLEDs remain in need of significant improvement. Accordingly, there remains an unmet need in the art for improved host materials that can efficiently and stably transport holes, electrons, and/or excitons into contact with blue phosphorescent guests in OLED emission layers.

[00016] It is to that end that the various inventions and embodiments related to the 2-alkyl-5-phenyl- l ,3,4-oxadiazole-carbazole ("2-APOC") small molecules described below are directed.

SUMMARY OF THE INVENTION

[00017] The various inventions and/or their embodiments disclosed herein relate to and include 2-alkyl-5-phenyl- l ,3,4-oxadiazole-carbazole ("2-

APOC") small molecules having both hole carrying and electron carrying groups bound therein, and the use of such small molecules as host materials for carrying holes, electrons, and/or excitons into contact with guest emitters, for use in the emissive layers of electronic devices such as organic light emitting diodes.

[00018] Accordingly, in many embodiments, the various inventions disclosed and claimed herein relate to 2-alkyl-5-phenyl- l ,3,4-oxadiazole-carbazole compounds, i.e. 2-APOC compounds, having one or more carbazole groups bound to the 5-phenyl ring of the oxadiazole compound , the compounds having the formula:

wherein

a. at least one of the R¹, R² and R³ groups comprises a monocarbazole group, biscarbazole group, or triscarbazole group optionally substituted with one or more fluoride or organic substituent groups; and the remaining R¹, R² or R³ groups are independently selected from hydrogen, fluoride, or organic substituent groups; and b. R⁴ is selected from a branched, mono-, bi- or tricyclic alkyl group optionally substituted with independently selected alkoxide, fluoroalkoxide, aryl, or heteroaryl groups.

[00019] The inventions described herein also relate to methods of making the 2-APOC compounds and compositions comprising them, especially compositions wherein the 2-APOC compounds are hosts for guest emitter compounds, and can be unexpectedly superior hosts for blue emissive guest compounds, for use in OLED emissive layers, and the OLED devices themselves.

[00020] Further detailed description of preferred embodiments of the various compound disclosed and claimed herein, and methods and materials for their preparation, and preparation of the corresponding compositions and OLED devices will be provided in the Detailed Description section below.

BRIEF DESCRIPTION OF THE FIGURES

[00021 ] Figure la shows the structures of compounds YZ-1I1-257, YZ-III-287 and ΥΖ-ΙΠ-305, and Figures lb, lc, and Id show cyclic voltammograms of each compound in THF. See Example 3.

[00022] Figure 2a shows non-gated emission specta of YZ-III-287 in 2-methyl THF at room temperature solution and in a 77 K glass. Figure 2b shows gated and non-gated emission spectra of YZ-III-287 in 2-methyl THF in a 77 glass. See Example 3.

[00023] Figure 3a shows non-gated emission specta of YZ-III-257 in 2-methyl THF at room temperature solution and in a 77 glass. Figure 3b shows gated and non-gated emission spectra of YZ-III-257 in 2-methyl THF in a 77 K glass. See Example 3.

[00024] Figure 4a shows the schematic structure diagram of OLEDs employing compound YZ-III-287 as a host for Ir(ppy)₃ emitter, Figures 4b and 4c show results of the luminescence testing of the OLEDs. See Example 5.

[00025] Figure 5a shows the schematic structure diagram of alternative OLEDs employing compound YZ-III-287 as a host for Ir(ppy)₃ emitter, Figures 5b and 5c show results of the luminescence testing of the OLEDs. See Example 6.

[00026] Figure 6a shows the schematic structure diagram of alternative OLEDs employing compound YZ-III-287 as a host for Ir(ppy)₃ emitter, Figures 6b and 6c show results of the luminescence testing of the OLEDs. See Example 7.

[00027] Figure 7a shows the schematic structure diagram for OLEDs employing compound YZ-III-287 as a host for FIrpic emitter, Figures 7b and 7c show results of the luminescence testing of the OLEDs. See Example 8.

[00028] Figure 8a shows the schematic structure diagram for alternative OLEDs employing compound YZ-III-287 as a host for FIrpic emitter, Figures 8b and 8c show results of the luminescence testing of the OLEDs. See Example 9. [00029] Figure 9a shows the schematic structure diagram for OLEDs employing compound YZ-III-305 as a host for FIrpic emitter, Figures 9b and 9c show results of the luminescence testing of the OLEDs. See Example 10.

[00030] Figure 10a shows the schematic structure diagram for alternative OLEDs employing compound YZ-III-305 as a host for FIrpic emitter, Figures 10b and 10c show results of the luminescence testing of the OLEDs. See Example 1 1.

[00031 ] Figure 11a shows the schematic structure diagram for alternative OLEDs employing compound YZ-III-305 as a host for FIrpic emitter, Figures lib and 11c show results of the luminescence testing of the OLEDs. See Example 12.

[00032] Figures 12a and 12b show results of the luminescence testing of the OLEDs comprising compound YZ-III-257 as a host for Firpic emitter, see Comparative Example 13.

[00033] Figure 13 shows drawings depicting the frontier molecular orbitals of compound YZ-III-287 as calculated from the results of the molecular orbital calculations described in the specification. ,

DETAILED DESCRIPTION OF THE INVENTION

[00034] The various inventions and/or their embodiments disclosed herein relate to 2-alkyl-5-phenyl-l ,3,4-oxadiazole-carbazole compounds, i.e. 2- APOC compounds, which comprise both hole carrying and electron carrying groups. Those 2-APOC compounds are useful as host materials for luminescent guest emitters, including blue guest emitters, and are capable of carrying holes, electrons, and excitons into efficient contact with such guests. The host/guest compositions comprising the 2-APOC compounds described herein are useful as materials for making the emissive layers of electronic devices such as organic light emitting diodes (OLEDs).

2-Alkyl-5-Phenyl-l,3,4-Oxadiazole-Carbazole Compounds

[00035] Many embodiments of the inventions described and/or claimed herein relate to novel 2-alkyl-5-phenyl- l ,3,4-oxadiazole-carbazole compounds having one or more carbazole groups bound to the 5-phenyl ring, the compound having the formula:

wherein

a. at least one ofthe R'. R² and R³ groups comprises a monocarbazole group, biscarbazole group, or triscarbazole group optionally substituted with one or more fluoride, cyano, or a C 1 -C20 linear or branched alkyl, fluoroalkyl, alkoxide, or fluoroalkoxide groups; and the remaining R¹, R² or R³ groups are independently selected from hydrogen, fluoride, cyano, or a linear or branched alkyl, fluoroalkyl, alkoxide, or fluoroalkoxide group; and

b. R⁴ is selected from normal, branched, mono-, bi- or tricyclic alkyl groups optionally substituted with independently selected alkoxide, fluoroalkoxide, aryl, or heteroaryl groups.

[00036] The 2-alkyl-5-phenyl-l ,3,4-oxadiazole-carbazole compounds can have one or more carbazole groups bound to the 5-phenyl ring at the R¹, R² and R³ positions can be independently selected from monocarbazole groups, biscarbazole groups, or triscarbazole groups, which can optionally substituted with one or more fluoride, cyano, or a C1 -C20, C1 -C12, or C i -C₆ organic groups, such as for example linear or branched alkyl, fluoroalkyl, alkoxide, or fluoroalkoxide groups. The remaining R¹, R² or R³ positions on the 5-phenyl group of the oxadizole can be independently selected from hydrogen, fluoride, cyano, or a C1 -C20 C 1 -C12, or C1-C6 organic groups, such as for example linear or branched alkyl, fluoroalkyl, alkoxide, or fluoroalkoxide groups.

[00037] In many preferred embodiments, the one or more carbazole groups are bound to the 5-phenyl ring of the oxadizole at the "meta" R¹ and R³ positions, rather than the "para" R² position. Without wishing to be bound by theory, it is believed (based on the results of molecular orbital calculations described below) that electrons injected from the OLED cathode tend to localize on LUMO orbitals on the oxadiazole and 5-phenyl rings, and that holes from the OLED anodes tend to localize in HOMO orbitals on the carbazole rings, and that due to molecular orbital and geometric effects, the "meta" R¹ and/or R³ positions of the 5-phenyl ring provide for less overlap and/or conjugation between the orbitals on the carbazole and oxadiazole groups, with the result that at least some non-radiative charge transfer decay pathways are partially blocked or slowed down, so as to inhibit the decay of excitons formed on the 2-alkyl-5-phenyl-l ,3,4-oxadiazole-carbazole compounds. The result of these electronic effects are that the excitons may have longer lifetimes, and can therefore be more likely to transfer their energy to the emissive guests.

[00038] In many embodiments, wherein the optionally substituted monocarbazole groups, biscarbazole groups, or triscarbazole groups can have the structures

wherein Ar is a C1-C12 aryl or heteroaryl ring such as phenyl, biphenyl, pyridyl, and the like, and R⁵, R⁵ R⁶, and R⁶ can be independently selected from hydrogen, fluoride, cyano , and a C1-C6 organic group selected from linear and branched alkyls, fluoroalkyls, alkoxides, and fluoroalkoxides, and R is a C1-C30 linear, branched mono-, bi- or tricyclic alkyl. In such embodiments, R⁵, R⁵ , R⁶, and R⁶ can also be independently selected from hydrogen and t-butyl, or are all hydrogen.

[00039] As can be readily seen, the monocarbazole, biscarbazole, and triscarbazole groups can be bonded to the 5-phenyl ring of the oxadiazole at any position on the carbazole phenyl rings, or to the nitrogen atom of the carbazole. However, the monocarbazole, biscarbazole, and triscarbazole groups must be bound to the R¹, R², or R³ positions of the 5-phenyl ring of the oxadiazole. In many embodiments, it is preferred that the monocarbazole, biscarbazole, and triscarbazole groups be bound to the R¹ or R³ "meta" positions of the 5-phenyl ring of the oxadiazole, since binding at the R¹ or R³ "meta" positions of the 5-phenyl ring is (without wishing to be bound by theory) to significantly weaken or effectively prevent the introduction of undesirable low energy charge transfer absorptions from the carbazole -centered HOMO orbitals to the oxadiazole centered LUMO that could result in the presence of low energy triplet states resulting from such low energy charge transfer absorptions.

[00040] In some embodiments of the 2-alkyl-5-phenyl- 1 ,3,4- oxadiazole-carbazole compounds, one of the R¹, R² and R³ groups is an optionally substituted monocarbazole or tricarbazole group, and the remaining R , R or R groups are hydrogen, resulting in compounds having structures such as

wherein R⁵, R⁵ , R⁶, and R⁶ can be independently selected from hydrogen, fluoride, cyano , and a Ci-C₆ organic group preferably selected from linear and branched alkyls, fluoroalkyls, alkoxides, and fluoroalkoxides. In such embodiments, R⁵, R⁵ ,

6 6' '

R°, and R° can also be independently selected from hydrogen and t-butyl, to give compounds such as the one shown below:

[00041 ] In some embodiments of the 2-alkyl-5-phenyl- l ,3,4- oxadiazole-carbazole compounds the R¹ and R³ groups are an optionally substituted monocarbazole group and R² is hydrogen, resulting in compounds having structures such as

wherein R⁵ and R⁶ are independently selected from hydrogen, fluoride, cyano , and a C1-C6 organic group preferably selected from linear and branched alkyls, fluoroalkyls, alkoxides, and fluoroalkoxides. In such embodiments, R⁵, R⁵ , R⁶, and R⁶ can also be independently selected from hydrogen and t-butyl., or R⁵, R⁵ , R⁶, and R⁶ are all hydrogen, such as the compounds shown below:

[00042] In the 2-alkyl-5-phenyl- 1 ,3,4-oxadiazole-carbazole compounds, R⁴ is selected from a C1-C30, C1-C20, or C1-C12 normal, branched, mono-, bi- or tricyclic alkyl group optionally substituted with one to five independently selected alkoxide, fluoroalkoxide, aryl, or heteroaryl groups.

[00043] As already noted above, certain 2, 5-diphenyl-l ,3,4- oxadiazole-carbazole compounds are known in the prior art as ambipolar host materials for guest emitters in OLED devices. Without wishing to be bound by theories, it is believed that removing the 2-phenyl groups from such compounds and replacing them with alkyl groups reduces the degree of electronic conjugation in the LUMO of the molecules that are largely localized on the 5-phenyl oxadiazole electron carrying groups of molecules and raises their LUMO energy, with the result that the optical bandgaps and/or lowest triplet energy states of the 2-alkyl-5-phenyl- 1 ,3,4-oxadiazole-carbazole compounds, are at least somewhat higher than those of equivalent 2, 5-diphenyl- l ,3,4-oxadiazole-carbazole compounds known in the prior art.

[00044] As detailed below in Example 3 and in Figures , cyclic voltammetry measurement of YZ-IlI-287, with a methyl group at R⁴, confirm that YZ-III-287 has a significantly more negative solution reduction potential, by about 0.15 eV, than that of YZ-1I1-257 with a 3-methoxyphenyl group at R⁴. Additionally, the emission spectroscopic measurements of YZ-III-287 and YZ-III-257 at 77 K in 2-methyl THF indicate that the lowest energy triplet excited state of YZ-III-287 is at about 2.88 eV, which is at about 0.16 eV higher energy of the comparable lowest triplet energy of YZ-III-257 (2.72 eV).

[00045] As will be further elaborated below, it appears that because the compounds of the present inventions with alkyl groups at R⁴ have higher energy triplet excited states than prior art compounds with phenyl groups at R⁴, that the 2- APOC compounds described and claimed herein may be unexpectedly superior hosts for higher photon energy blue guest emitters than the prior art 2,5-diphenyl- oxadiazole-carbazole compounds.

[00046] Also, use of varying the alkyl groups at R⁴ also provides a ready opportunity and mechanism for "fine-tuning" both the lowest triplet state energies and/or the solubility and/or solid state properties of the 2-APOC compounds, so modify their processability, degree of crystallinity and/or amorphous properties, physical interactions with the guest emitters, etc.

[00047] In many embodiments of the 2-alkyl-5-phenyl- 1 ,3,4- oxadiazole-carbazole compounds, R⁴ is selected from a C1-C30, C1-C20, or C1-C12 normal, branched, mono-, bi- or tricyclic alkyl group. In some embodiments, R⁴ is a C1-C12 normal or branched alkyl group. In some embodiments, R⁴ is a CH3 group.

[00048] In some embodiments, R⁴ comprises or is a C1-C12

monocyclic, bicyclic or tricyclic alkyl group. In some embodiments, R⁴ comprises or is a cyclopentane, a cyclohexane, a bicyclo[2.2.1 ]heptane, a bicyclo[2.2.2]octane or adamantane group. In some embodiments, R is a group having the structures shown below:

Comparative Calculated Electronic Properties of the 2-Alkyl-5-Phenyl-l,3,4- Oxadiazole-Carbazole Compounds

[00049] Density Functional Theory (DFT) molecular orbital calculations of the ionization potentials (IP), electron affinities (EA), and lowest triplet state energies (corresponding to S0"->T1 transitions) for the a compound of the invention (YZ-III-287) as compared to the compound YZ-III-305 having a CF3 group at R⁴, were the subject of molecular orbital calculations at the B3LYP/6- 31 G** level of theory.

YZ-III-287 _and YZ-lll-305

[00050] The results of the molecular orbital calculations carried out are shown below in Table 1, and a drawing of the calculated frontier orbitals of YZ- III-287 is shown in Figure 13.

[00051 ] A general result of the molecular orbital calculations, as illustrated in the drawings of Figure 13, was that that the highest occupied molecular orbital (HOMO) of YZ-III-287 is largely localized on the carbazoles, and extends to some carbon atom positions on the 5-phenyl ring of the oxadizole (at least when the carbazole is attached at a "meta" position on the 5-phenyl ring of the compound).

[00052] The highest unoccupied molecular orbital (LUMOs) of YZ- 287 is localized on the oxadiazole ring and some positions on the attached 5-phenyl ring. See Figure 13. According to the calculations, YZ-III-305, with a CF3 group at R⁴, has similar localizations, but the details of the calculated energetics are significantly different.

[00053] As seen in Table 1 the LUMO and lowest triplet excited state energies of YZ-III-287, - 1.73 and 3.22 eV respectively, are significantly higher than those of YZ-III-305, at -2.19 and 3.09 eV, see Table 1. It seems that the strong electron withdrawing inductive effect of the trifluoromethyl group of YZ-III-305 somewhat selectively lowers the energy of the LUMO.

Table 1

Compound HOMO LUMO S0"^T1

(eV) (eV) ASCF (eV)

YZ-III-287 R" = CH₃ -5.53 - 1.73 3.22

YZ-III-305 R⁴ = CF₃ -5.68 -2.19 3.09

[00054] As a result of all of the above, the 2-aIkyl-5-phenyl- 1 ,3,4- oxadiazole-carbazole compounds described and claimed herein, with their relatively high energy LUMOs and/or lowest triplet excited states, should have the unexpected advantage of being capable of serving as an efficient host for a wider range of higher energy blue emitting guests than the otherwise similar compounds with

trifluoroalkyl groups at R⁴, such as YZ-III-305.

Methods for Making The Compounds

[00055] Several generic methods for making many of the 2-alkyl-5- phenyl- l ,3,4-oxadiazole-carbazole compounds of the invention, wherein R⁴ can be either an alkyl, fluoroalkyl, or optionally substituted version thereof are indicated in

C11/K2CO3

DMF

[00056] Specific examples of two such compounds, one wherein R⁴ is CH3, and one wherein R⁴ is CF3 are provided in Examples 1 and 2. Synthesis of compounds wherein the carbazoles are attached to the 5-phenyl ring of the oxadiazole via a bond to a phenyl ring atom of the carbazole rather than the nitrogen atom of the carbazole can be readily prepared by well known palladium catalyzed cross couplings of appropriate carbazole borates or stanane derivatives with 2-alkyl- 5-bromophenyl-l ,3,4-oxadiazoles.

OLEDs Comprising the Polymers and Copolymer Blends

[00057] Some aspects of the present inventions relate to novel organic electronic devices, especially organic light emitting diodes (OLED) devices that comprise the 2-alkyl-5-phenyl-l ,3,4-oxadiazole-carbazole compounds described herein as components of host blend compositions for making the emission layers of OLEDs.

[00058] Although other alternatives are known in the art, in many embodiments, the OLED devices comprise at least an anode layer, a hole transporting layer, an emission layer, an electron transporting layer, and a cathode layer. Such devices are illustrated in the diagram below:

^■ Cathode Layer

Electron Transporting Layer

Emission Layer

Hole Transporting Layer

- Anode Layer

- Glass

OLED Device

[00059] Accordingly, in many embodiments of the OLED devices disclosed herein, the OLEDs comprise the following layers:

a. an anode layer,

b. a hole transporting layer,

c. an emissive layer,

d. an electron transporting layer, and

e. a cathode layer. '

[00060] In many embodiments of the OLED devices disclosed herein, the emissive layer employ one or. more of the 2-alkyl-5-phenyl- l ,3,4-oxadiazole compounds described and/or claimed herein to form unexpectedly superior hosts for guest emitters, as compared to the known prior art, especially for use with high energy blue emitters.

[00061 ] Indium tin oxide (ITO) is a well known example of a suitable transparent semiconducting material for making the anode layers of OLEDs, although others are known to those of ordinary skill in the art, and can be employed within the scope of the current inventions.

[00062] ITO is often applied by sputtering in a layer over an inert and transparent substrate such as glass. Suitable ITO coated glass plates are available from Colorado Concept Coatings LLC, with a sheet resistivity of ~15 Ω/sq, which was used as the substrate for the OLEDs fabrications described herein. The commercially ITO coated substrates were prepared for use in the example devices described herein by patterning them with kapton tape and were then etched in acid vapor ( 1 :3 by volume, HNO3: HC1) for 5 min at 60 °C. The coated and treated substrates were cleaned in an ultrasonic bath of detergent water, rinsed with deionized water, and then cleaned in sequential ultrasonic baths of deionized water, acetone, and isopropanol. Each ultrasonic bath lasted for 20 minutes. Nitrogen was used to dry the substrates after each of the last three baths.

[00063] Many materials are potentially useful as hole transporting layers, including both monomeric or polymeric carbazole compounds. Well known small molecule hole carrying materials that are typically applied by vacuum evaporation to form hole carrying layers for OLEDs include a-NPD (commercially available from Lumtec of Hsin-ChuTaiwan), and mCP, which was made via well known literature methods.

a-NPD mCP

[00064] Polymeric hole carrying materials for use in the devices of the inventions described herein include for example polyvinyl carbazole (PVK, commercially available from Sigma Aldrich ) which can be dissolved in a solvent such as toluene, and spun-coated onto the ITO substrates. Disclosed and claimed herein for the first time in Example 4 is a somewhat analogous new polyvinyltriscarbazole compound, YZ-IV-17 whose structure is shown below. As compared with PVK, YZ-IV-17 is believed to have higher lowest triplet energy levels, and therefore may be more compatible with higher energy blue emitters than PVK.

YZ-IV-17

Poly(6-(9H-carbazol-9-yl)-9-(4- vinylbenzyl)-9H-3,9'-bicarbazole)

[00065] PEDOT: PSS A14083, commercially available from Heraeus of Hanau Germany is an aqueous dispersion of Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate), structure shown below. PEDOT: PSS is typically spin coated

(60s@1500 rpm, acceleration 10,000 rpm/s) onto ITO coated glass substrates, in a

N₂ filled wet glove box, to form a hole-transporting layer with a thickness of about

40 nm.

PDOT: PSS

[00066] The 2-alkyl-5-phenyl- l ,3,4-oxadiazole compounds described and claimed herein are typically employed as host materials for forming the emissive layers of OLEDs. The emissive layers of OLEDs can be formed from these materials by co-depositing them (as hosts) with luminescent guest emitters, under vacuum. Alternatively, the emissive layers can be formed by dissolving the 2- alkyl-5-phenyl-l ,3,4-oxadiazole compounds in common organic solvents such as toluene, chlorobenzene, and the like, and the guest emitters, and spin coating the solutions over the hole carrying layers.

[00067] The guest emitters potentially suitable for use with the 2- APOC compounds described herein as a host are most typically a metal complex wherein the metal is selected from Re, Ru, Os, Rh, Ir, Pd, Pt, Cu and Au, and in some embodiments, the guest emitters are complexes of Iridium, Platinum, and other 3d row transition metals, see for example US 2006/0127696, or WO 2009/026235, the teachings of both of which are hereby incorporated by reference herein . Commonly used green emitters include Ir(ppy)3 (Y. Kawamura et al. Appl. Phys. Lett. 2005, 86, 071 104/1 ), Ir(pppy)₃ (US 2006/127696), and Ir(mppy)₃ (H. Wu et al. Adv. Mater. 200

Ir(PPy)3, Firpic

[00068] A well-known and commercially available blue-green emitter often employed as a "representative" guest emitter in studies of OLED devices in the literature is Firpic (Y. Kawamura et al. Appl. Phys. Lett. 2005, 86, 071 104/1 ). It is however known that Firpic is actually however only has a lowest triplet state energy of around 2.65-2.70 eV, and emits in the "greenish blue" region of the color spectrum (CIE coordinates 0.17, 0.34), and is not ideally suitable as a higher energy "deep blue" emitter that would be best suited for applications in flat panel displays, see Eom et al, App. Phys. Lett. 93, 133309 (2008). Several of the Examples below employ Firpic as a "blue" guest emitter to produce highly efficient OLED devices.

[00069] However, it appears, based on the evidence discussed in Example 3 and in Example 13 that at least some of the 2,5-diphenyl-oxadiazole- carbazoles also have lowest triplet energies that may be barely adequate for use with Firpic. However, unlike the 2-APOC compounds described and claimed herein, the 2,5-diphenyl-oxadiazoles likely do not have sufficiently energetic lowest excited states to serve as hosts for higher energy "deep blue" guest emitters.

[00070] A number of such higher energy "deep blue" emitters are known in the art, see for example, FIr₆ (T. Sajoto et al. Inorg. Chem. 2005, 44, 7992- 8003, and Eom et al cited above), "FIrtaz" and "FIrN4" (Yun Chi in Adv Mater 2005, 17, 285), and "Irdbfmi" ( Sasabe, Kido,et al, Adv Mater 2010, 22, 5003). The 2-APOC compounds claimed herein can be suitable hosts for such high energy blue emitters, and show unexpectedly improved results as compared to 2,5-diphenyl- oxadiazole-carbazoles known in the prior art.

[00071 ] Many organic materials are suitable as electron transporting and/or hole blocking materials, such as a variety of substituted phenanthrolines, such as bathocuproine (BCP = 2,9-dimethyl-4,7-diphenyl- l , 10-phenanthroline, BCP, or various oxadiazoles, such as PBD, which are commercially available and can be readily applied to the^'devices via vacuum/thermal deposition techniques well known in the art.

[00072] Many materials can be suitable as cathode layers, one example being a combination of lithium fluoride (LiF) as an electron injecting material coated with a vacuum deposited layer of Aluminum, and optionally an additional layer of silver.

Electroluminescent Properties of the PLED Devices

[00073] Results of the electrolum inescent testing of a number of exemplary OLED devices comprising the 2-alkyl-5-phenyl- l ,3,4-oxadiazole- carbazole compound YZ-1II-287 as host for both green emitting lr(ppy)3 and blue- green emitting FIrpic are described in the Examples 2-6 below. In most of the examples, devices comprising YZ-III-287 as host result in potentially very bright OLED devices with peak brightness often above 10⁴ cd/m², and relatively low turn- on voltages, in the range of 3-6 volts. External Quantum Efficiencies to rival the best results known in the prior art for any OLEDs, in a practical range of 16-12% were obtained with both green emitting Ir(ppy)3 and blue-green emitting Firpic, and the EQE numbers (see especially Example 8 and Figure 7) are believed to at least equal to, and potentially be unexpectedly superior to the prior art known to

Applicants in connection with the use of deeper blue emitters.

[00074] Furthermore, although the comparative results discussed immediately below do constitute prior art to the current Application, the 2-alkyl-5- phenyl-l ,3,4-oxadiazole-carbazole compounds described and claimed herein, such as YZ-III-287, are unexpectedly superior to the very similar trifluoromethyl compound YZ-III-305. See Examples 11 and 12, and Figures 10c and 11c, which show the External Quantum Efficiencies obtained when YZ-III-305 is used with the blue-green emitter Firpic are much lower than those obtained using YZ-III-287.

[00075] Furthermore, the results obtained when using the 2-alkyl-5- phenyl-l ,3,4-oxadiazole-carbazole compounds described and claimed herein, such as YZ-III-287, are at least equal to those obtained with the 2,5-diphenyl-oxadizole- carbazole YZ-III-257 when it is used with the blue-green emitter Firpic (see Comparative Example 13 and Figure 1 l c), which results are believed to be unexpectedly superior to the prior art results known to Applicants that employ Firpic. However, as noted and discussed above, the 2-alkyl-5-phenyl- 1 ,3,4- oxadiazole-carbazole compounds described and claimed herein, such as YZ-III-287, have lowest triplet energy states that are believed to be significantly higher than those of the 2,5-diphenyl-oxadizole-carbazoles such as YZ-III-257. Accordingly, it is believed that the 2-alkyl-5-phenyl-l ,3,4-oxadiazole-carbazole compounds described and claimed herein, such as YZ-III-287 can be compatible with and serve as hosts for a wider and higher photon energy range of guest blue emitters than can 2,5-diphenyl-oxadiazole-carbazo|es such as YZ-III-307, or many or all alternative host materials known in the prior art. EXAMPLES

[00076] The various inventions described above are further illustrated by the following specific examples, which are not intended to be construed in any way as imposing limitations upon the scope of the invention disclosures or claims attached herewith. On the contrary, it is to be clearly understood that resort may be had to various other embodiments, modifications, and equivalents thereof which, after reading the description herein, may suggest themselves to one of ordinary skill in the art without departing from the spirit of the present invention or the scope of the appended claims.

[00077] General - All experiments with air- and moisture-sensitive intermediates and compounds were carried out under an inert atmosphere using standard Schlenk techniques. NMR spectra were recorded on either a 400 MHz Varian Mercury spectrometer or a 400 MHz Bruker AMX 400 and referenced to residual proton solvent. UV-vis absorption spectra were recorded on a Varian Cary 5E UV-vis-NIR spectrophotometer, while solution and thin-film PL spectra were recorded on a Fluorolog III ISA spectrofluorometer. Lifetime measurements were taken using a PTI model C-72 fluorescence laser spectrophotometer with a PTI GL- 3300 nitrogen laser. Cyclic voltammograms were obtained on a computer controlled BAS 100B electrochemical analyzer, and measurements were carried out under a nitrogen flow in deoxygenated DMF solutions of tetra-«-butylammonium hexafluorophosphate (0.1 M). Glassy carbon was used as the working electrode, a Pt wire as the counter electrode, and an Ag wire anodized with AgCl as the pseudo- reference electrode. Potentials were referenced to the ferrocenium/ferrocene (FeCp2^{+ 0}) couple by using ferrocene as an internal standard. Gel-permeation chromatography (GPC) analyses were carried out using a Waters 1525 binary pump coupled to a Waters 2414 refractive index detector with methylene chloride as an eluent on American Polymer Standards 10 μιη particle size, linear mixed bed packing columns. The flow rate used for all measurements was 1 ml/min, and the GPCs were calibrated using poly(styrene) standards. Differential scanning calorimetry (DSC) data were collected using a Seiko model DSC 220C. Thermal gravimetric analysis (TGA) data were collected using a Seiko model TG DTA 320. Inductively coupled plasma-mass spectrometry (ICP-MS) for platinum and ruthenium was provided by Bodycote Testing Group. Ή-NMR and ¹³C-NMR spectra (300 MHz Ή NMR, 75 MHz ¹³C NMR) were obtained using a Varian Mercury Vx 300 spectrometer. All spectra are referenced to residual proton solvent. Abbreviations used include singlet (s), doublet (d), doublet of doublets (dd), triplet (t), triplet of doublets (td) and unresolved multiplet (m). Mass spectral analyses were provided by the Georgia Tech Mass Spectrometry Facility. The onset of thermal degradation for the polymers was measured by thermal gravimetric analysis (TGA) using a Shimadzu TGA-50. UV/vis absorption measurements were taken on a Shimadzu UV-2401 PC recording spectrophotometer. Emission measurements were acquired using a Shimadzu RF-5301 PC spectrofluorophotometer. Lifetime measurements were taken using a PTI model C-72 fluorescence laser spectrophotometer with a PTI GL-3300 nitrogen laser. Elemental analyses for C, H, and N were performed using Perkin Elmer Series II CHNS/O Analyzer 2400. Elemental analyses for iridium were provided by Galbraith Laboratories.

[00078] Unless otherwise noted, cited reagents and solvents were purchased from well-known commercial sources (such as Sigma-Aldrich of Milwaukee Wisconsin or Acros Organics of Geel Belgium, and were used as received without further purification.

Example 1 - Synthesis of YZ-III-287; 2-(3,5-di(9H-carbazol-9-vnphenvn-5- methyl- 1 ,3 ,4-oxad iazole

[00079] Compound YZ-III-287 (structure shown below) was synthesized and characterized as outlined below;

YZ-III-287

2-(3,5-di(9H-carbazol-9-yl)phenyl)- 5-methyl-1 ,3.4-oxadiazole

methyl 3,5-di(9H-carbaz<^9-yl)benzoate

[00080] Methyl 3,5-di(carbazol-9-yl)benzoate (YZ-III-241): To a solution of methyl 3,5-diiodobenzoate (20.0 g, 51.55 mmol), carbazole (20.0 g,

1 19.6 mmol), Cu (80.0 g, 1.25 mol) and 18-crown-6 (300.0 mg, 1.15 mmol) in 1 ,2- dichlorobenzene (200.0 ml) was added potassium carbonate (80.0 g, 0.58 mol) under nitrogen and stirring. The reaction was carried out at 170°C (oil bath) for 7 h. After cooling, the reaction mixture was filtrated. The solid residues were carefully washed with THF. THF and 1 ,2-dichlorobenzene were evaporated from the combined filtration solution. The product was purified by silica gel column chromatography using toluene as eluent. Final pure product was obtained in 19.0 g (78.8%) by recrystallization from acetone/methanol:

[00081 ] ¹H NMR (CDCl₃): 8 8.37 (d, J = 1.6 Hz, 1 H), 8.15 (dd, J_/ =

7.2 Hz, J2 = 0.8 Hz, 4 H), 8.02 (t, J = 1.6 Hz, 1 H), 7.52 (dd, J, = 7.2 Hz, J₂ = 0.8 Hz, 4 H), 7.45 (td, J, = 7.2 Hz, J₂ = 1.6 Hz, 4 H), 7.32 (td, J,= 7.2 Hz, J₂ = 1.2 Hz, 4 H), 3.99 (s, 3 H, OCH₃) ppm. ^I3C NMR (CDC1₃): δ 165.39, 140.18, 139.54, 133.63, 129.09, 126.45, 126.20, 123.62, 120.55, 120.43, 109.42, 52.82 ppm. MS (El) m/z (%): 466.0 (100%) [M⁺]. Anal. Calcd for C32H22N2O2: C, 82.38; H, 4.75; N, 6.00.

Found: C, 82.34; H, 4.66; N, 6.03.

3,5-di(9H-carbazol-9-yl)benzohydrazide [00082] 3,5-Dicarbazol-9-ylbenzhydrazide (YZ-III-263): To a solution of methyl 3,5-di(carbazol-9-yl)benzoate ( 1 0.0 g, 0.52 mol) in dioxane (1 00.0 ml) and ethanol (70.0 ml) was added hydrazine hydrate (20.0 ml). The reaction mixture was refluxed for 6 hours. The reaction mixture was cooled down to room temperature and water (380.0 ml) was added. The white product solid was collected by filtration, washed with water and dried under vacuum. The yield of the reaction is 10.0 g (1 00.0 %). This crude compound can be used for the next step without further purification.

[00083] " H NMR (400 MHZ, CDC1₃) 5: 8. 13 (dd, J, = 7.6 Hz, J₂ = 0.8 Hz, 4 H), 8.05 (d, J = 2.0 Hz, 2 H), 7.98 (t, J= 2.0 Hz, 1 H), 7.52 (s, br, 1 H, NH), 7.50 (dd, J, = 7.6 Hz, J₂ = 0.8 Hz, 4 H), 7.43 (td, J, = 7.6 Hz, J₂ = 0.8 Hz, 4 H), 7.3 1 (td, J, = 1.6 Hz, J₂ = 0.8 Hz, 4 H), 4. 1 6 (br, 2 H, NH₂) ppm. ¹³C NMR ( 100 MHz, CDC1₃) 5: 1 66.85, 140.23, 139.99, 136.14, 128.09, 126.3 1 , 123.85, 1 23.73, 120.73, 120.55, 109.42 ppm. From the NMR, it appeared the crude compound contained some methanol.

YZ-lll-281

/V-acetyl-3,5-di(9H-carbazol-9-yl)benzohydrazide

[00084] N'-Acetyl-3,5-dicarbazol-9-ylbenzohydrazide (YZ-III- 281): To a solution of 3,5-Dicarbazol-9-ylbenzhydrazide (1 .0 g, 2. 14 mmol) in dry tetrahydrofuran (20.0 ml) was slowly added acetyl chloride (0.2 g, 2.55 mmol) at 0°C under nitrogen. After addition of acetyl chloride, the reaction was warmed up to room temperature and the reaction mixture was stirred at room temperature for 2.5 hours. Pyridine (5.0 ml) was added and stirred for another 30 min. The reaction mixture was poured into water ( 1 50.0 ml). The white solid was collected by filtration, washed with water and dried overnight under vacuum to give in 1 .02 g (93.6 %) yield. This compound can be used for the next step without any purification.

[00085] Ή NMR (400 MHz, CDCI₃) 8: 1 1.42 (s, 1 H, NH), 8.30 (d, J = 2.0 Hz, 2 H), 8.27 (d, J = 8.0 Hz, 4 H), 8.19 (t, J = 2.0 Hz, 1 H), 7.62 (d, J = 8.0 H = 8.0 Hz, 4 H), 7.32 (t, J = 8.0 Hz, 4 H), 3.33 (s, 1 H, NH) ppm.

YZ-l!l-287

2-(3,5-di(9H-carbazol-9-yl)phenyl)- 5-methyl-1 ,3,4-oxadiazole

[00086] 2-(3,5-Di(carbazol-9-yl)phenyl)-5-methyl-l,3,4-oxadazole

(YZ-III-287): N'-Acetyl-3,5-dicarbazol-9-ylbenzohydrazide ( 1.0 g, 1 .97 mmol) was added in POCI3 (20.0 ml). The reaction was heated to 90 °C and kept at this temperature for 4 hours. After cooling down to room temperature the reaction mixture was poured into ice-water (500.0 ml). The white solid formed was collected by vacuum filtration. The crude product was dried and purified by silica gel chromatography using dichloromethane/ethyl acetate (9.5:0.5) as eluent. After removal of solvents, pure product as white solid was obtained in 0.53 g (55.2%) yield.

[00087] Ή NMR (400 MHz, CDCI3) δ: 8.38 (d, J= 2.0 Hz, 2 H), 8.17

(dd, J_/ = 8.0 Hz, J₂ = 1.2 Hz, 4 H), 8.00 (t, J= 2.0 Hz, 1 H), 7.57 (d, J = 8.0 Hz, 4 H), 7.46 (td, J i = 8.0 Hz, J₂ = 1.2 Hz, 4 H), 7.33 (td, J, = 8.0 Hz, J₂ = 1.2 Hz, 4 H), 2.64 (s, 3 H, CH₃) ppm. ¹³C NMR (100 MHz, CDCI3) δ: 164.33, 163.62, 140.40, 140.23, 127.65, 127.38, 126.37, 123.81 , 123.42, 120.78, 120.57, 109.51 , 1 1 .51 ppm. MS-EI (m/z): [M]⁺ Calcd for C₃3H₂2N₄0: 490.2, 491 .2, 492.2, found 490.2, 491 .2, 492.2. Anal. Calcd for C33H22N4O: C, 80.80; H, 4.52; N, 1 1 .42. Found: C, 80.92; H, 4.49; N, 1 1 .25. Example 2 - Synthesis of YZ-III-305a: 2-(3.5-Dircarbazol-9-yl)phenvn-5-f2- (trifluoromethyl)-l,3,4-oxadazole

[00088] Compound YZ-III-305a (structure shown below) was synthesized and characterized as outlined below;

Y2-lll-305a

2-(3,5-di(9H-cart>azol-9-yl)phenyl)- 5-(trifluoromethyl)-1,3,4-oxadiazol8

YZ-lll-289

3,5-di(9H-carbazol-9-yl)-A ^,-(2,2,2- trifluoroacetyl)benzohydrazide

[00089] N'-(2,2,2-Trifluoroacetyl)-3,5-di(carbazol-9- yl)benzohydrazide (YZ-III-289): To a solution of 3,5-Dicarbazol-9- ylbenzhydrazide (1.0 g, 2.14 mmol) in dry tetrahydrofuran (20.0 ml) was slowly added trifluoroacetic anhydride (0.6 g, 2.86 mmol) at 0°C under nitrogen. After addition of 4-methylbenzoyl chloride, the reaction was warmed up to room temperature and the reaction mixture was stirred at room temperature for 5 hours. Pyridine (5.0 ml) was added and stirred for another 30 min. The reaction mixture was poured into water (200.0 ml). The white solid was collected by filtration, washed with water and dried overnight under vacuum to give in 1 .10 g (87.3 %) yield. This compound can be used for next step without any purification. [00090] Ή NMR (400 MHz, CDC1₃) δ: 1 1.20 (s, 1 H, NH), 1 1.07 (s, 1 H, NH), 8.30 (d, J = 2.0 Hz, 2 H), 8.27 (d, J = 8.0 Hz, 4 H), 8.16 (t, J = 2.0 Hz, 1 H), ppm.

YZ-lll-305a

[00091 ] 2-(3,5-Di(carbazol-9-yl)phenyl)-5-(2-(trinuoromethyl)- 1,3,4-oxadazole (YZ-III-305a): N'-(2-Trifluoromethyl)-3,5-di(carbazol-9- yl)benzohydrazide (1.0 g, 1.78 mmol) was added in POCI3 (20.0 ml). The reaction was heated to 90 °C and kept at this temperature for 6 hours. After cooling down to room temperature the reaction mixture was poured into ice-water (600.0 ml). The solid formed was collected by vacuum filtration. The crude product was dried and purified by silica gel column using dichloromethane/hexanes (3: 1 ) as eluent. After removal of solvents, pure product as white solid was obtained in 0.21 g (21.6%) yield.

[00092] Ή NMR (400 MHz, CDC1₃) δ: 8.46 (d, J = 2.0 Hz, 2 H), 8.16 (dd, J, = 8.0 Hz, J₂ = 1.6 Hz, 4 H), 8.10 (t, J = 2.0 Hz, 1 H), 7.56 (d, J= 8.0 Hz, 4 H), 7.48 (td, Jj = 8.0 Hz, J₂ = 1.6 Hz, 4 H), 7.36 (td, J, = 8.0 Hz, J₂ = 1.6 Hz, 4 H) ppm. ^{, 3}C NMR ( 100 MHz, CDC1₃) δ: 165.23, 140.89, 140.14, 129.25, 126.50, 125.57, 124.07, 123.94, 121.02, 120.68, 1 17.52, 1 14.81 , 109.35 ppm. ¹⁹F NMR (CDCI3, CF3COOH) δ: -65.77 (s, 3 F) ppm. MS-El (m/z): [M]⁺ Calcd for

C33H,₉F₃N40: 544.2, 545.2. Found 544.1 , 545.4. Anal. Calcd for C₃3H,9F3N₄0: C, 72.79; H, 3.52; N, 10.29. Found: C, 72.97; H, 3.39; N, 10.17.

Example 3 - Comparative Cyclic Voltammetry and Emission Spectroscopy of YZ-III-257. YZ-III-287 and YZ-III-305 [00093] The compound shown below, YZ-III-257, ie. 2-(3,5- Dicarbazol-9-ylphenyl)-5-(3-methoxyphenyl)-l ,3,4-oxadiazole, methods for its synthesis, and OLED devices comprising the compound were reported in PCT Application PCT/EP2010/058732 filed 21 June 2010, which is hereby incorporated herein by reference in its entirety.

[00094] Cyclic voltammograms were recorded for YZ-III-257, YZ-III- 287 and YZ-III-305 in THF (0.1 M (n-Bu)₄NPF₆ in THF, E/V (vs

Ferrocene/Ferrocenium⁺ cation as an internal standard, Pt Working electrode; Pt wire counter electrode; Ag/AgCl reference electrode; 50 mV/s scanning rate). The cyclic voltammograms are shown in Figures lb, lc, and Id.

[00095] YZ-III-287, with a methyl group at the 2-position of the oxadizole group showed a reversible reduction at -2.53 V, which occurs at a more negative (higher energy) reduction potential than YZ-III-257 (-2.38 V, reversible) which has a 3-methoxyphenyl group at the 2-position of the oxadiazole. YZ-III-305, with a trifluoromethyl-group at the 2-position of the oxadiazole, had a significantly lower reduction potential, -2.19 V, irreversible. The reason for the electrochemical irreversibility of the reduction of YZ-III-305 is unknown.

[00096] It appears that the strongly electron withdrawing inductive effect of the trifluoromethyl group on the oxadizole may significantly lower the energy of the LUMO of YZ-III-305, as compared to the LUMO of YZ-III-287 with a methyl group at the 2-position, or even the LUMO of YZ-III-257 (with a methoxyphenyl group at the 3-position of the oxadiazole). Molecular orbital calculations described above reach the same conclusion. The relatively low energy of the LUMO and/or lowest triplet excited state of YZ-III-305 probably makes it relatively undesirable for use with high energy blue guest emitters. [00097] Emission spectra were also recorded for YZ-III-287 and YZ- III-257 in dilute 2-methyl THF glasses at 77 , see Figures 2a, 2b, 3a, and 3b. Figure 2a shows a room temperature non-gated emission spectrum (excitation at 300nm) of YZ-III-287 in dilute 2-methyl THF solution, and shows a broad emission band with a peak at 403 nm. A second non-gated emission spectrum of YZ-III-287 from the 77 glass resolves multiple emission peaks, including a peak at 367 nm that likely corresponds to fluorescent emission from a lowest singlet excited state, then vibronically coupled phosphorescent emission peaks from about 425-550 nm.

[00098] The non-gated emission spectrum of YZ-III-287 from the 77 glass is also reproduced in Figure 2b, along with a pulsed excitation, time-gated emission spectrum of the same material in the 77 K glass. The pulsed

excitation/time-gating procedure preferentially detects phosphorescent emissions as shown in the second spectrum in Figure 2b, which had a highest energy peak at 430 nm, which likely corresponds to emission from the non-vibrationally relaxed lowest triplet state of YZ-III-287 at an energy of 2.88 eV.

[00099] Figure 3a shows a room temperature non-gated emission spectrum (excitation at 300nm) of YZ-II1-257 in dilute 2-methyl THF solution, and shows a broad emission band with a peak at 420 nm. A second non-gated emission spectrum of YZ-III-257 from the 77 K glass resolves multiple emission peaks, including a peak at 378 nm that likely corresponds to fluorescent emission from a lowest singlet excited state, then vibronically coupled phosphorescent emission peaks out to an energy of about 550 nm.

[000100] The non-gated emission spectrum of YZ-III-257 from the 77 glass is also reproduced in Figure 3b, along with a pulsed excitation, time-gated emission spectrum of the same material in the 77 glass. The pulsed

excitation/time-gating procedure preferentially detects phosphorescent emissions as shown in the second spectrum in Figure 3b, which had a highest energy peak at 456 nm, which likely corresponds to emission from the non-vibrationally relaxed lowest triplet state of YZ-III-257 at an energy of 2.72 eV.

[000101 ] From these spectral data it can be concluded that the lowest triplet excited state of YZ-III-287, at 2.88 eV, is likely about 0.16 eV higher in energy than the comparable lowest triplet excited state of YZ-III-257, at 2.72 eV. [000102] Example 4 -Synthesis of A Novel Solution Processible Hole Transmission Polymeric Material, YZ-IV-17, Polv(6-(9H-carbazol-9-yl)-9-

YZ- 1 II -279

(6-(9H-carbazol-9-yl)-9-(4-vinylbenzyl)- gH-S^-bicarbazole)

YZ-IV-17

Poly(6-(9H-carbazol-9-yl)-9-(4- vinylbenzyl)-9H-3,9'-bicarbazole)

[000103] Solution processible hole carrying polymers are well known in the art, such as for example polyvinylcarbazole, PVK. Applicants have however invented an alternative polyvinyl hole carrying polymer having triscarbazole attached (YZ-IV-17, Poly^-^H-carbazol^-y ^-H-vinylbenzy ^H-S^¹- bicarbazole)) that is very easily synthesized and solution processible, and is amorphous but has a very high glass transition temperature. Applicants have found that YZ-IV-17 produces unexpectedly superior results in some OLED applications as a hole transmitting material, as compared with PVK, at least in some of the devices evaluated herein, especially for use with blue guest emitters such as Firpic. Accordingly, the synthesis of YZ-IV-17 is reported in this example. [000104] Tris-carbazole monomer (YZ-III-279, 6-(9H-carbazol-9- yl)-9-(4-vinylbenzyl)-9H-3,9'-bicarbazoIe): To a solution of Tris-carbazole (3.0 g, 6.03 mmol) and l-(chloromethyl)-4-vinylbenzene (1.5 g, 9.83 mmol) in DMF (40.0 ml) was added ₂C0₃ (10 g, 72.36 mmol) at room temperature under stirring. The reaction was carried out at room temperature for 52 h. Water (200.0 ml) was added. The white solid product was obtained by filtration, washed with water and methanol. After dry, the crude product was purified by silica gel column chromatography using dichloromethane/hexanes (6 : 4) as eluent. After removal of solvent, The white solid product was obtained and collected from hexanes by filtration. After vacuum dry, the product YZ-III-279 was collected as a white solid in 3.55 g (95.9%) yield.

[000105] Ή NMR (400 MHz, CDCI3) δ: 8.25 (s, 2 H), 8.17 (d, J = 8.0 Hz, 4 H), 7.63 (d, J= 1.2 Hz, 4 H), 7.44-7.37 (m, 10 H), 7.30-7.26 (m, 6 H), 6.72 (dd, J_/ = 17.6 Hz, J₂ = 10.8 Hz, 1 H, C=C-H), 5.76 (d, J = 17.6 Hz, 1 H, C=C-H), 5.68 (s, 2 H, NCH₂), 5.27 (d, J = 10.8 Hz, 1 H, C=C-H) ppm. ¹³C NMR (100 MHz, CDC1₃) 8: 141 .76, 140.34, 137.32, 136.16, 135.99, 129.79, 126.86, 126.79, 126.16, 125.84, 123.62, 123.10, 120.26, 1 19.83, 1 19.64, 1 14.33, 1 10.33, 109.71 , 46.96 ppm. MS-EI (m/z): [M]⁺ calcd for C45H₃₁N₃, 613.3, 614.3, 615.3, 616.3, found 613.2, 614.2, 615.2, 616.2. Anal. Calcd for C₄₅H₃iN₃: C, 88.06; H, 5.09; N, 6.85. Found: C, 87.15; H, 5.03; N, 6.50.

[000106] Poly(triscarbazole) (YZ-IV-17, Poly(6-(9H-carbazol-9-yl)- 9-(4-vinylbenzyl)-9H-3,9'-bicarbazole)): A Schlenk flask was charged with tris- carbazole monomer YZ-III-279 (1.0 g, 1.6 mmol),;AIBN (7.0 mg, 0.042 mmol) and dry THF (20.0 ml). The polymerization mixture was purged with nitrogen (removal of oxygen), securely sealed under nitrogen, and heated to 60°C. The polymerization was carried out at 60°C with stirring for 7 days. After cooling to room temperature, the polymer was precipitated with acetone. The white polymer precipitate was collected by filtration, dissolved in dichloromethane, and precipitated with acetone again. This dissolution/precipitation procedure was repeated three more times. The collected polymer was dried under vacuum. After vacuum dry, the polymer as white solid in 0.93 g (93.0 %) was obtained.

[000107] 'H-NMR(400 MHZ, CDC1₃) δ: 8.09 (m, br, 10 H), 7.16 (m, br, 16 H), 5.28 (m, br, 2 H), 1.25-0.75 (m, br, 3 H) ppm. Anal. Calcd for C₄₅H₃|N₃: C, 88.06; H, 5.09; N, 6.85. Found: C, 87.58; H, 5.04; N, 6.68. GPC (CHC1₃): M_w = 29000, M_n = 14000, PDI = 2.0. DSC: Tg = 296°C.

[000108] Example 5 - An PLED Device Employing YZ-III-287 As A Host For A Green Ir(ppyV¾ Emitter

[000109] An OLED device employing YZ-III-287 as a host for

Ir(ppy)3, a well known green emitter, and having the detailed configuration shown in Figure 4a (Glass/ITO/PVK/YZ-III-287, Ir(ppy)3, 6 wt% BCP/LiF:AI) was prepared as follows;

[0001 10] Indium tin oxide (ITO)-coated glass (Colorado Concept Coatings LLC) with a sheet resistivity of 15 Ω/sq was used as the substrate for the OLEDs fabrication. The ITO substrates were patterned with kapton tape and etched in acid vapor (1 :3 by volume, HNO3: HC1) for 5 min at 60 °C. The substrates were cleaned in an ultrasonic bath of detergent water, rinsed with deionized water, and then cleaned in sequential ultrasonic baths of deionized water, acetone, and isopropanol. Each ultrasonic bath lasted for 20 minutes. Nitrogen was used to dry the substrates after each of the last three baths. Finally all substrates were treated with an 0₂ plasma for 3 minutes prior to the deposition of the organic layers. The same procedures were used to prepare the ITO substrates for all the subsequent examples.

[0001 1 1] For the PVK hole-transport layer, 10 mg of PVK were dissolved in 1 ml of 99.8% toluene which was distilled and degassed over night prior to be used. 35 nm thick PVK layers were spin coated (60s@1500 rpm, acceleration 10,000 rpm/s) onto the plasma-treated. ITO coated glass substrates. Samples where then transferred into a SPECTROS thermal deposition system, Kurt J. Lesker, for the evaporative deposition of the remaining layers.

[0001 12] A 20 nm thick emissive layer consisting of YZ-III-287 and Ir(ppy)3 was co-deposited, with an Ir(ppy)3 concentration of 6 wt.%, in the

SPECTROS system at a pressure below 10^"7 Torr and at rates of 1 and 0.06 A/s respectively.

[0001 13] Then, for the hole-blocking and electron transport layer, a 40 nm thick BCP layer was deposited at a pressure below 2* 10^"7 Torr and at rates of 0.4 A/s. A 2.4 nm of lithium fluoride (LiF), as an electron-injection layer, and a 200 . nm-thick aluminum layer were sequentially deposited through a shadow mask at a pressure below 3 χ 10^"7 Torr and at rates of 0.15 A/s and 2 A/s, respectively. The shadow mask used for the evaporation of the metal electrodes yielded five devices with an area of roughly 0.1 cm² per substrate. Analogous procedures were used in all the subsequent examples.

[0001 14] In this and all the following examples, the testing of the finished OLEDs using a standard photometric characterization set-up were done right after the deposition of the metal cathode, in inert atmosphere and without exposing the devices to air.

[0001 15] The results of the testing of the devices are shown in Figures 4b and 4c. As can be seen in Figure 4c, the device was very bright, with a peak luminance of over 10⁴ cd/m², and very good peak External Quantum Efficiencies of over 16%.

[0001 16] Example 6 - An PLED Device Employing YZ-III-287 As A Host For A Green Ir(ppy)¾ Emitter

[0001 17] An OLED device employing YZ-III-287 as a host for Ir(ppy)3, a well known green emitter, and having the detailed configuration shown in Figure 5a (Glass/ITO/YZ-IV-17/YZ-III-287, Ir(ppy)₃, 6 wt%/BCP/LiF:Al:Ag) was prepared as follows;

[0001 18] A glass/ITO substrate prepared as described above was spin coated with YZ-iV-17 dissolved in 1 ml of 99.8% pure chlorobenzene. 35 nm thick YZ-IV- 17 layers were spin coated (60s@1500 rpm, acceleration 10,000 rpm/s) onto plasma-treated ITO coated glass substrates. Samples where then transferred into an in an EvoVac thermal deposition system, Angstrom Engineering, for the evaporation of the remaining layers.

[0001 19] A 20 nm thick emissive layer consisting of YZ-IIl-287and Ir(ppy)3 was co-deposited, with an Ir(ppy)3 concentration of 6 wt.%, in the EvoVac system at a pressure below 10^"7 Torr and at rates of 1 and 0.06 A/s respectively.

[000120] Then, for the hole-blocking and electron transport layer, a 40 nm thick BCP layer was deposited at a pressure below 2* 10^"7 Torr and at rates of 0.4 A/s. [000121 ] A 2.4 nm of lithium fluoride (LiF), as an electron-injection layer, and a 40 nm-thick aluminum layer were sequentially deposited through a shadow mask at a pressure below 3 ^x 10^"7 Torr and at rates of 0.15 A/s and 2 A/s, respectively. The cathode was then finished by depositing a 100 nm thick silver layer, through the same shadow mask as LiF and Al, at a pressure below 3 < 10^"7 Torr and at a rate of 1 .1 A/s. The shadow mask used for the evaporation of the metal electrodes yielded five devices with an area of roughly 0.1 cm² per substrate. The testing was done right after the deposition of the metal cathode in inert atmosphere and without exposing the devices to air.

[000122] The results of the testing of the devices are shown in Figures 5b and 5c. As can be seen in Figure 5c, the device was very bright, with a peak luminance of over 10⁴ cd/m², and very good peak External Quantum Efficiencies of about 14%, at relatively low operating voltages of 5-6 V.

[000123] Example 7 - An PLED Device Employing YZ-III-287 As A Host For A Green Ir(ppy) Emitter

[000124] An OLED device employing YZ-III-287 as a host for Ir(ppy)3, a well known green emitter, and having the detailed configuration shown in Figure 6a, but with different hole transmitting layers (Glass/ITO/PEDOT:PSS/a- NPD/YZ-III-287, Ir(ppy)3, 6 wt%/BCP/LiF:Al:Ag) was prepared as follows;

[000125] A glass/ITO substrate prepared as described above was spin coated with PEDOT: PSS A14083 solution (60s@5000 rpm, acceleration 10,000 rpm/s) onto plasma-treated ITO coated glass substrates. After spin-coating, the PEDOT: PSS layers were baked for 10 minutes at 140 °C on a hot plate. Samples where then transferred into an in an EvoVac thermal deposition system, Angstrom Engineering, for the evaporation of the remaining layers.

[000126] For the hole transport layer, a 35 nm thick a-NPD was deposited on top of the PEDOT:PSS layer at a pressure below 2* 10^"7 Torr and at a rate of 0.6 A/s.

[000127] Then, a 20 nm thick emissive layer consisting of YZ-III-287 and Ir(ppy)3 was co-deposited, with an Ir(ppy)3 concentration of 6 wt.%, in the EvoVac system at a pressure below 10^'7 Torr and at rates of 1 and 0.06 A/s respectively. [000128] Then, for the hole-blocking and electron transport layer, a 40 nm thick BCP layer was deposited at a pressure below 2 10^'7 Torr and at rates of 0.4 A/s. A 2.4 nm of lithium fluoride (LiF), as an electron-injection layer, and a 40 nm-thick aluminum layer were sequentially deposited through a shadow mask at a pressure below 3 ^χ 10^"7 Torr and at rates of 0.15 A/s and 2 A/s, respectively. The cathode was then finished by depositing a 100 nm thick silver layer, through the same shadow mask as LiF and Al, at a pressure below 3x 10^"7 Torr and at a rate of 1 .1 A/s. The shadow mask used for the evaporation of the metal electrodes yielded five devices with an area of roughly 0.1 cm² per substrate.

[000129] The results of the testing of the devices are shown in Figures 6b and 6c. As can be seen in Figure 6c, the device was very bright, with a peak luminance of well over 10⁴ cd/m², a low turn-on voltage of less than 3 volts, and good peak External Quantum Efficiencies of about 10%.

[000130] Example 8 - An PLED Device Employing YZ-III-287 As A Host For A Blue FIrpic Emitter

[000131 ] An OLED device employing YZ-III-287 as a host for the well known blue emitter FIrpic, and having the detailed configuration shown in Figure 7a, but with different hole transmitting layers (Glass/ITO/YZ-iV-17/YZ-III-287, FIrpic 10 wt%/BCP/LiF;Al:Ag) was prepared as follows;

[000132] A glass/ITO substrate prepared as described above was spin coated with 10 mg of YZ-IV- 17 were dissolved in 1 ml of 99.8% pure

chlorobenzene. 35 nm thick YZ-IV-17 layers were spin coated (60s@1500 rpm, acceleration 10,000 rpm/s) onto plasma-treated ITO coated glass substrates.

Samples where then transferred into an in an EvoVac thermal deposition system, Angstrom Engineering, for the evaporation of the remaining layers.

[000133] A 20 nm thick emissive layer consisting of YZ-III-287 and FIrpic was co-deposited, with an FIrpic concentration of 10 wt.%, in the EvoVac system at a pressure below 10^"7 Torr and at rates of 1 and 0.1 A/s respectively.

[000134] Then, for the hole-blocking and electron transport layer, a 40 nm thick BCP layer was deposited at a pressure below 2x 10^'7 Torr and at rates of 0.4 A/s. A 2.4 nm of lithium fluoride (LiF), as an electron-injection layer, and a 40 nm-thick aluminum layer were sequentially deposited through a shadow mask at a pressure below 3 ^χ 10^"7 Torr and at rates of 0.15 A/s and 2 A/s, respectively. The cathode was then finished by depositing a 100 nm thick silver layer, through the same shadow mask as LiF and Al, at a pressure below 3 x 10^"7 Torr and at a rate of 1 .1 A/s. The shadow mask used for the evaporation of the metal electrodes yielded five devices with an area of roughly 0.1 cm² per substrate. The testing was done right after the deposition of the metal cathode in inert atmosphere and without exposing the devices to air.

[000135] The results of the testing of the devices are shown in Figures 7b and 7c. As can be seen in Figure 7c, the device was very bright, with a peak luminance of well over 1 0⁴ cd/m², a reasonably low turn-on voltage of about 4 volts, and very good peak External Quantum Efficiencies of 12% at 1 ,000 cd/m².

[000136] Example 9 - An PLED Device Employing YZ-III-287 As A Host For A Blue FIrpic Emitter

[000137] Another OLED device employing YZ-III-287 as a host for the well known blue emitter FIrpic, and having the detailed configuration shown in Figure 8a, but with different hole transmitting layers (Glass/ITO/PEDOT:PSS/a- NPD/mCp/YZ-III-287, FIrpic 10 wt%/BCP/LiF:Al:Ag) was prepared as follows;

[000138] A glass/lTO substrate prepared as described above was spin coated with PEDOT: PSS A14083 solution (60s@5000 rpm, acceleration 10,000 rpm/s) onto plasma-treated ITO coated glass substrates. After spin-coating, the PEDOT: PSS layers were baked for 10 minutes at 140 °C on a hot plate. Samples where then transferred into an in an EvoVac thermal deposition system, Angstrom Engineering, for the evaporation of the remaining layers.

[000139] For the hole transport layer, a 35 nm thick a-NPD was deposited on top of the PEDOT:PSS layer at a pressure below 2* 10^'7 Torr and at a rate of 0.6 A/s. Then a 1 5 nm thick mCP layer was deposited on top of the alpha- NPD at a pressure below 2x 10^"7 Torr and at rates of 0.5 A/s.

[000140] A 20 nm thick emissive layer consisting of YZ-III-287 and FIrpic was then co-deposited, with an FIrpic concentration of 10 wt.%, in the EvoVac system at a pressure below 10^"7 Torr and at rates of 1 and 0. 1 A/s

respectively. [000141 ] Then, for the hole-blocking and electron transport layer, a 40 nm thick BCP layer was deposited at a pressure below 2x 10^"7 Torr and at rates of 0.4 A/s. A 2.4 nm of lithium fluoride (LiF), as an electron-injection layer, and a 40 nm-thick aluminum layer were sequentially deposited through a shadow mask at a pressure below 3 * 10^"7 Torr and at rates of 0.15 A/s and 2 A/s, respectively. The cathode was then finished by depositing a 100 nm thick silver layer, through the same shadow mask as LiF and Al, at a pressure below 3* 10^"7 Torr and at a rate of 1 .1 A/s. The shadow mask used for the evaporation of the metal electrodes yielded five devices with an area of roughly 0.1 cm² per substrate. The testing was done right after the deposition of the metal cathode in inert atmosphere and without exposing the devices to air.

[000142] The results of the testing of the devices are shown in Figures 8b and 8c. As can be seen in Figure 8c, the device was very bright, with a peak luminance of well over 10⁴ cd/m², a reasonably low turn-on voltage of just over 3 volts, and External Quantum Efficiencies of 10% at a luminance of 10³ cd/m².

[000143] Example 10 - An PLED Device Employing YZ-III-305 As A Host For A Green Ir(ppy)3 Emitter

[000144] An OLED device employing YZ-III-305 as a host for the well known green emitter Ir(ppy)3, and having the detailed configuration shown in

Figure 9a, (Glass/ITO/YZ-III-305/YZ-III-305, Ir(ppy)₃ 6 wt%/BCP LiF:Al:Ag) was prepared as follows;

[000145] A glass/ITO substrate prepared as described above was spin coated with 10 mg of YZ-IV-17 were dissolved in 1 ml of 99.8% pure

chlorobenzene. 35 nm thick YZ-IV-17 layers were spin coated (60s@ l 500 rpm, acceleration 10,000 rpm/s) onto plasma-treated ITO coated glass substrates.

Samples where then transferred into an in an EvoVac thermal deposition system, Angstrom Engineering, for the evaporation of the remaining layers.

[000146] A 20 nm thick emissive layer consisting of YZ-III-305 and Ir(ppy)3 was co-deposited, with an Ir(ppy)3 concentration of 6 wt.%, in the EvoVac system at a pressure below 10^"7 Torr and at rates of 1 and 0.06 A/s respectively.

[000147] Then, for the hole-blocking and electron transport layer, a 40 nm thick BCP layer was deposited at a pressure below 2x 10^"7 Torr and at rates of 0.4 A/s. A 2.4 nm of lithium fluoride (LiF), as an electron-injection layer, and a 40 nm-thick aluminum layer were sequentially deposited through a shadow mask at a pressure below 3* 10^"7 Torr and at rates of 0.15 A/s and 2 A/s, respectively. The cathode was then finished by depositing a 100 nm thick silver layer, through the same shadow mask as LiF and Al, at a pressure below 3x 10^"7 Torr and at a rate of 1.1 A/s. The shadow mask used for the evaporation of the metal electrodes yielded five devices with an area of roughly 0.1 cm² per substrate. The testing was done right after the deposition of the metal cathode in inert atmosphere and without exposing the devices to air.

[000148] The results of the testing of the devices are shown in Figures 9b and 9c. As can be seen in Figure 9c, the device was bright, with a peak luminance of over 10⁴ cd/m², a turn-on voltage of just about 4 volts.

[000149] Example 11 - An PLED Device Employing YZ-III-305 As A Host For A Blue Emitter FIrpic

[000150] An OLED device employing YZ-III-305 as a host for the well known blue emit'er FI^rpic, and having the detailed configuration shown in Figure 10a, (Glass/ITO/PEDOT:PSS/a-NPD/mCp YZ-III-305. Firpic 10 wt%

/BCP LiF A Ag) was prepared as follows;

[000151 ] A glass/ITO substrate prepared as described above was spin coated with PEDOT: PSS A14083 solution (60s@5000 rpm, acceleration 10,000 rpm/s) onto plasma-treated ITO coated glass substrates. After spin-coating, the PEDOT: PSS layers were baked for 10 minutes at 140 °C on a hot plate. Samples where then transferred into an in an EvoVac thermal deposition system, Angstrom Engineering, for the evaporation of the remaining layers.

[000152] For the hole transport layer, a 35 nm thick a-NPD was deposited on top of the PEDOT:PSS layer at a pressure below 2^X 10^"7 Torr and at a rate of 0.6 A/s. Then a 15 nm thick mCP layer was deposited on top of the alpha- NPD at a pressure below 2x l 0^'7 Torr and at rates of 0.5 A/s. Then a 15 nm thick mCP layer was deposited on top of the alpha-NPD at a pressure below 2x 10^~7 Torr and at rates of 0.5 A/s.

[000153] A 20 nm thick emissive layer consisting of YZ-III-305 and FIrpic was then co-deposited, with an FIrpic concentration of 10 wt.%, in the EvoVac system at a pressure below 10^"7 Torr and at rates of 1 and 0.1 A/s

respectively.

[000154] Then, for the hole-blocking and electron transport layer, a 40 nm thick BCP layer was deposited at a pressure below 2x 10^"7 Torr and at rates of 0.4 A/s. A 2.4 nm of lithium fluoride (LiF), as an electron-injection layer, and a 40 nm-thick aluminum layer were sequentially deposited through a shadow mask at a pressure below 3* 10^"7 Torr and at rates of 0.1 5 A/s and 2 A/s, respectively. The cathode was then finished by depositing a 100 nm thick silver layer, through the same shadow mask as LiF and Al, at a pressure below 3* 10^"7 Torr and at a rate of 1.1 A/s. The shadow mask used for the evaporation of the metal electrodes yielded five devices with an area of roughly 0.1 cm² per substrate. The testing was done right after the deposition of the metal cathode in inert atmosphere and without exposing the devices to air.

[000155] The results of the testing of the devices are shown in Figures 10b and 10c. As can be seen in Figure 10c, the device was bright, with a peak luminance of over 10⁴ cd/m², a turn-on voltage of just about 4 volts, and a highest peak External Quantum Efficiencies of about 6%.

[000156] Example 12 - An PLED Device Employing YZ-III-305 As A Host For A Blue Emitter FIrpic

[000157] An OLED device employing YZ-III-305 as a host for the well known blue emitter FIrpic, and having the detailed configuration shown in Figure 11a, (Glass/ITO/YZ-rV- 17/YZ-III-305, Firpic 10 wt% /BCP/LiF:Al:Ag) was prepared as follows.

[000158] A glass/ITO substrate prepared as described above was spin coated with 10 mg of YZ-IV-17 dissolved in 1 ml of 99.8% pure chlorobenzene. 35 nm thick YZ-IV-17 layers were spin coated (60s@1500 rpm, acceleration 10,000 rpm/s) onto plasma-treated ITO coated glass substrates. Samples where then transferred into an in an EvoVac thermal deposition system, Angstrom Engineering, for the evaporation of the remaining layers.

[000159] A 20 nm thick emissive layer consisting of YZ-III-305 and FIrpic was co-deposited, with an FIrpic concentration of 10 wt.%, in the EvoVac system at a pressure below 10^'7 Torr and at rates of 1 and 0.1 A/s respectively. [000160] Then, for the hole-blocking and electron transport layer, a 40 nm thick BCP layer was deposited at a pressure below 2x 10^"7 Torr and at rates of 0.4 A/s. A 2.4 nm of lithium fluoride (LiF), as an electron-injection layer, and a 40 nm-thick aluminum layer were sequentially deposited through a shadow mask at a pressure below 3x 10^'7 Torr and at rates of 0.15 A/s and 2 A/s, respectively. The cathode was then finished by depositing a 100 nm thick silver layer, through the same shadow mask as LiF and Al, at a pressure below 3* 10^"7 Torr and at a rate of 1.1 A/s. The shadow mask used for the evaporation of the metal electrodes yielded five devices with an area of roughly 0.1 cm² per substrate. The testing was done right after the deposition of the metal cathode in inert atmosphere and without exposing the devices to air.

[000161 ] The results of the testing of the devices are shown in Figures lib and 11c. As can be seen in Figure 11c, the device was bright, with a peak luminance of around 10⁴ cd/m², a turn-on voltage of just about 4 volts, and External Quantum Efficiencies of about 4-6%.

[000162] Comparative Examples 13 - An PLED Device Employing YZ-III-257 As A Host For A Blue Emitter FIrpic

[000163] The compound shown below, YZ-III-257, ie. 2-(3,5- Dicarbazol-9-ylphenyl)-5-(3-methoxyphenyl)- l ,3,4-oxadiazole, methods for its synthesis, and OLED devices comprising the compound were reported in

Applicants' PCT Application PCT/EP2010/058732 filed 21 June 2010, which is hereby incorporated here

[000164] An OLED device employing YZ-III-257 as a host for the well known blue emitter FIrpic, and having the detailed configuration (Glass/ITO/PVK YZ-III-257/ Firpic 10 wt% BCP/LiF:Al) was prepared via a procedure very similar to the device preparations above, except for the absence of a silver layer in the cathode. [000214] The current- voltage characteristic of the above referenced comparative devices are shown in Figure 12a. The light output and external quantum efficiency as a function of voltage are shown in Figure 12b.

[000165] As can be seen in Figure 12b, maximum External Quantum Efficiencies reached 6-7%.

[000166] Example 14 - Synthesis of DF-1-45

[000167]

Synthesis of DF-I-23:

A mixture of carbazole (24 g, 144 mmol) and acetic acid (360 mL) was heated to 80 °C, and then finely-crushed potassium iodide (31 .5 g, 1 89 mmol) was added. After a few minutes of stirring, potassium iodate (24 g, 100 mmol) was carefully added in small increments, and the system was maintained at 80 °C until the resulting iodine was fully consumed. The mixture was cooled to 40 °C and filtered, followed by washing with 30 mL acetic acid, 1 00 mL methanol and water sequentially, resulting in 51 g yellow solid of 3,6-Diiodo-9H-carbazole. Yield: 90%. Ή NMR (300 MHz, CDC13, δ): 8.33 (m, 2H), 8.15 (m, 1 H), 7.70-7.60 (m, 2H), 7.23-7.20 (m, 2H).

Synthesis of DF-I-25:

To this solution, di-/er/-butyl dicarbonate (6.2 g, 14.4 mmol) was first added, and then 4-dimethylaminopyridine (2 g, 14.4 mmol) was carefully added in small increments (gas evolved). After stirring for 4 hours at room temperature, the precipitate was filtered, the reaction mixture was concentrated to half volume, and the precipitate was filtered again. The same procedure was repeated once more and the precipitates were combined and washed with methanol to give 4 g of DF-I- 25.Yield:90%. Ή NMR (300 MHz, CDC13, δ): δ 8.13 (2.0H, d, J = 1.5 Hz), 7.99 (2.0H, d, J = 8. = 8.8, 1.5 Hz), 1.74 (9.0H, s).

Synthesis of DF-I-29:

Carbazole (6 g, 36 mmol), DF-L-25 (4.7 g, 9.1 mmol), Cul (573 mg, 3 mmol), and K3P04 (6.36g, 30 mmol) were added to a 3-necked flask, and then (±)-trans- 1 ,2- cyclohexanediamine (340 mg, 3 mmol) and dioxane (120ml) were added under a nitrogen atmosphere. After stirring for 24h at 1 10°C, the reaction mixture was cooled to room temperature, diluted with toluene (1000 mL), filtered through silica gel, and the filtrate was concentrated. Purification by silica gel column chromatography (hexane : toluene=l : l ) gave the title compound 4.3 g. Yield:80%. Ή NMR (300 MHz, CDC13, δ): δ 8.60 (2H, d, J = 10 Hz), 8.17-8.16 (2.0H, m), 8.15-8.14 (4 H, m), 7.71 -60 (2H, dd, Jl = 2.7 Hz, 32 = 10 Hz), 7.41 -7.38(4H, m), 7.33-7.26 (2H, m), 1.3 1 (9H, s).

DF-l-31

Synthesis of DF-I-31 (compound 7):

[000168] DF-I-29 (1 g, 1.68 mmol) was dissolved in trifluoroacetic acid (3 mL). After stirring for another 4h, the reaction mixture was neutralized with aqueous potassium carbonate, and then the organic layer was separated, washed with brine, and dried over Na2S04.Upon removal of Na2S04 by filtration, the resulting solution was concentrated under reduced pressure to give white solid 0.8 g. Yield: 92%. Ή NMR (300 MHz, CDC13, δ): 8.50 (1 H, m), 8.18-8.14 (6.0 H, m), 7.65-7.62 (4H, m) , 7.46-7.38 (8H, m), 7.34-7.26 (4H, m).

[000169] Compound DF-I-45 (structure shown below) was synthesized and characterized as outlined below;

2-(3-(6-(9H-carbazol-9-yl)-9H-3,9^,

-bicarbazol-9-yl)phenyl)-5-methy ,3,4-oxadiazole

[000170] 10 g of 3-iodobenzohydrazine was placed in 100 mL of a sealed tube, and then 12.8 g 1,1, 1 -triethy lethane was added and then heated to 150 °C. After stirring overnight, the reaction solution was cooled to room temperature and resulted in white precipitate, filtration gave 10.2 g white solid 2-(3-iodophenyl)- 5-methyl-l,3,4-oxadiazole. Yield: 98%. Ή (300MHz, CDC13): δ 8.14 (m, IH), 7.90

[000171] Triscarbazdle (compound 7) (100mg, 1.4 mmol), 2-(3- iodophenyl)-5-methyl-l,3,4-oxadiazole (114mg, 40 mmol), Cul (38mg, 0.2mmol), and 3PO4 (84.8 mg, 0.4mmol) were added to a 3 -necked flask, and then (±)-trans- 1 ,2-cyclohexanediamine (23 mg, 0.2 mmol) and dioxane (3mL) were added under a nitrogen atmosphere. After stirring for 24h at 110°C, the reaction mixture was cooled to room temperature. Upon removal of the solvent under reduced pressure, the resulting residue was poured into saturated NH4CI aqueous solution and extracted with chloroform. The organic layer was separated and dried over sodium sulfate. Removal of sodium sulfate by filtration and solvent under reduced pressure afforded the title product (80 mg). Yield: 60%. Ή NMR (300 MHz, CDC13, δ): 8.44-8.43 (IH, m), 8.30-8.29 (2.0 H, m), 8.28-8.24 (IH, m), 8.18-8.17(2H, m), 8.16- 8.14 (2H, m), 7.95-7.92 (IH, m), 7.90-7.85 (IH, m), 7.70-7.62 (4H, m), 7.42-7.38 (4H, m), 7.34-7.34 (6H, m), 2.68 (3H,s). ^I3C{'H} (75MHZ, CDC13): 142.9, 141.01, 140.37, 138.1, 132.2, 131.2, 130.8, 130.1, 126.7, 126.5, 126.3, 125.9, 125.3, 124.2, 123.2, 120.3, 1 19.9, 1 19.8, 1 1 1 .5, 109.7, 1 1 .2. EI-MS (jn/z): M calcd for

C45H31N5O, 655.2; found 655.2. Elemental anal, calcd. for C45H29N5O: C, 82.42; H,

4.46; N, 10.68. Found: C, 82.26; H, 4.33; N, 10.64.

[000172] Example 15 - Synthesis of DF-I-67-3

[000173] Compound DF-I-67-3 (structure shown below) was synthesi

Synthesis of DF-I-53

[0001 74] A solution of 1 -admantanecarbonyl chloride ( 1 .6 g, 8 mmol) in dichloride (5 mL) was added dropwise to a solution of 3-iodobenzohydrazide(2.0 g, 7.6 mmol) and triethylamine (1.0 g, 10 mmol) in dichloride ( 15 mL) at 0°C with stirring. After stirring for an additional 3h at 0°C, saturated ammonium chloride (30 mL) was poured into the mixture, and the organic layer was separated and washed subsequently with saturated sodium biscarbonate aqueous solution (30 mL), water (30 mL) and dried over anhydrous sodium sulfate. Upon removal of sodium sulfate by filtration and solvent under reduced pressure, the resulting residue was rinsed with ether to give a white solid 980 mg. Yield: 27%. Ή (300MHz, CDC13): δ 10.4(s, 1 H), 8.6(s, 1 H), 8.35-8.34(m, 1 H), 8.04-8.00(m, 1 H), 7.85-7.81 (m, 1 H), 7.26-7.19(m, 1 H), 1.9 (s, 2H), 1.68-1.54(m, 13H). EI-MS (m/z): M⁺ calcd for C18H21 I 2O2, 424.28; found 425.1.

DF-l-58

Synthesis of DF-I-58:

[000175] A suspension of DF- 1-53 (2.0 g, 4.7 mmol) in phosphoryl trichloride (20 mL) was stirred in reflux overnight and cooled to room temperature. Then phosphoryl trichloride was removed under reduced pressure. The resulting residue was poured into ice-cold water and generated a white precipitate, which was extracted with dichloromethane and dried over sodium sulfate. Upon removal of sodium sulfate and solvent under reduced pressure, the resulting residue was purified by silica gel column chromatography (EtOAc:Hexane= 1 :4) to give a white powder (0.9 g). Yield: 50%. Ή (300MHz, CDC13) δ 8.35 (s, 1 H), 8.04-8.00(m, 1 H), 7.85-7.81 (m, 1 H), 7.26-7.20 (m, 1 H), 2.12 (m, 9H), 1.81 (m, 6H). ¹³C{ ^!H} (75MHz, CDC13): 172.9, 162.8, 140.2, 135.3, 130.6, 126.1 , 125.9, 94.3, 39.3, 36.3, 34.4, 27.7 . EI-MS (m/z) M⁺ calcd for CisH^E^O, 406.3; found 406.0.

Synthesis of DF-I-67-3:

[000176] Triscarbazole (compound 7) (280 mg, 0.69 mmol), 2-(3- iodophenyl)-5-methyl-l ,3,4-oxadiazole (230 mg, 0.8 mmol), Cul (20 mg, 0.1 mmol), and 3PO4 (1 g, 5 mmol) were added to a 3-necked flask, and then (±)- ira«i-l ,2-cyclohexanediamine (50 mg, 0.1 mmol) and dioxane (3 mL) were added under a nitrogen atmosphere. After stirring for 24h at 1 10°C, the reaction mixture was cooled to room temperature. Upon removal of the solvent under reduced pressure, the resulting residue was poured into saturated NH₄CI aqueous solution and extracted with chloroform. The organic layer was separated and dried over sodium sulfate. Removal of sodium sulfate by filtration and solvent under reduced pressure afforded the title product (450 mg). Yield: 83%. Ή NMR (300 MHz, CDC13, δ): 8.44-8.43 ( 1 H, m), 8.30-8.29 (2.0 H, m), 8.28-8.24 (1 H, m), 8.1 8- 8.17(2H, m), 8.16-8.14 (2H, m), 7.95-7.92 (1 H, m), 7.90-7.85 ( 1 H, m), 7.70-7.62 (4H, m), 7.42-7.38 (4H, m), 7.34-7.24 (6H, m), 2.68 (3H,s). ¹³C { ' H} (75MHZ, CDC/5): 173.2, 163.4, 141.7, 140.5, 138.1 , 13 1.1 , 130.9, 130.8, 130. 1 , 126.7, 126.5, 125.9, 125.5, 124.1 , 123.2, 120.3, 1 19.9, 1 19.8, 1 1 1 .2, 109.7, 40.0, 36.3, 34.6, 27.3. Elemental anal, calcd. for C54H41N5O: C, 83.59; H, 5.33; N, 9.03. Found: C, 83.15; H, 5. 17; N, 8.92. MALDY-MS (m/z): M⁺ calcd for C54H41N5O, 775.5; found 775.5.

Example 16 - Synthesis of DF-I-65-2

[000177] Compound DF-I-65-2 (structure shown below) was synth

DF-l-64 Synthesis of DF-I-64:

[000178] A solution of 1 -admantanecarbonyl chloride (2 g, 4.3 mmol) in dichloride (5 mL) was added dropwise to a solution of 3,5-di(9H-carbazole-9-yl) benzohydrazide (1.0 g, 4.6 mmol) and triethylamine (0.5 g, 5 mmol) in dichloride (15 mL) at 0 °C with stirring. After stirring for an additional 3h at 0 °C, saturated ammonium chloride (30 mL) was poured into the mixture, and then the organic layer was separated and washed subsequently with saturated sodium biscarbonate aqueous solution (30 mL) and water (30 mL) and dried over anhydrous sodium sulfate. Upon removal of sodium sulfate by filtration and solvent under reduced pressure, the resulting residue was rinsed with ether to give a white solid 980 mg. Yield: 27%. Ή (300MHz, CDC13): δ 8.64 (br, 1 H), 8.33 (s, 2H), 8.32(dd, J l = 1.5Hz, J2=5.1 Hz, 1 H), 7.9 l(d, J l=1.8Hz, 1 H), 7.47-7.37(m, 8H), 7.30-7.26(m, 6H), 1 .8-1 .4 (m, 15H). ¹³C{ 'H} (75MHz, CDC13): 140.2, 135.2, 128.7, 126.3, 124.3, 136.7, 120.6, 120.4, 109.4, 40.1 , 38.3, 36.1 , 27.7. MALDY-MS (m/z): M⁺ calcd for C42H₃₆N₄02, 628.6; fou

DF -1-65-2

[000179] Synthesis of DF-I-65-2

A suspension of DF-I-64 (0.7 g, 1.5 mmol) in phosphoryl trichloride (10 mL) was stirred in reflux overnight and cooled to room temperature. Then phosphoryl trichloride was removed under reduced pressure. The resulting residue was poured into ice-cold water and generated a white precipitation, which was extracted with dichloromethane and dried over sodium sulfate. Upon removal of sodium sulfate and solvent under reduced pressure, the resulting residue was purified by recrystallization from ethyl acetate to give a white powder (0.16g). Yield: 26%. Ή (300MHz, CDC 13): δ 8.39 (d, J= 2.1Hz, 2H), 8.20 (d, J= 4.8Hz, 4H), 7.99 (s, 1H), 7.60-7.56 (m, 4H), 7.45-7.39 (m, 4H), 7.28-7.25(m, 4H), 2.01-2.00(m, 8H), 1.73- 1.70(m, 6H). ⁱ³C{'H} (75MHz, C C7J): 173.2, 163.5, 141.7, 140.5, 138.1, 131.1, 130.1, 130.8, 130.1, 126.7, 125.9, 125.5, 124.1, 123.1, 120.3, 119.9, 119.8, 111.1, 40.0, 36.3, 34.5, 27.7. MALDY-MS (m/z): M⁺ calcd for C42H34N4O, 610.3; found 611.4.

[000180] Example 17 - Synthesis of DF-I-59-2

[000181] Compound DF-I-59-2 (structure shown below) was s

DF-l-49

Synthesis of DF-I-49:

[000182] A solution of cyclohexane carboxylate acid chloride (0.73 g, 5 mmol) in dichloride (5 mL) was added dropwise to a solution of 3,5-di(9H- carbazole-9-yl) benzohydrazide (1.0 g, 4.6 mmol) and triethylamine (0.5 g, 5 mmol) in dichloride (15 mL) at 0 °C with stirring. After stirring for an additional 3h at 0 °C, saturate ammonium chloride (30 mL) was poured into the mixture, and then the organic layer was separated and washed with saturated sodium biscarbonate aqueous solution (30 mL) and water (30 mL) and dried over anhydrous sodium sulfate. Upon removal of sodium ltration and solvent under reduced pressure, the resulting residue was rinsed with ether to give a white solid 1.73g. Yield: 60%. Ή (300MHz, CDC13): 5 9.8 (br, 1 H), 8.64 (s, 1 H), 8.12(s, 2H), 8.1 1 -8.07 (m, 4H), 7.91 (d, Jl = 1.8Hz, 1 H), 7.47-7.37(m, 8H), 7.30-7.26(m, 6H), 2.2-2.1 (m, 1 H), 1.73-1.62(m, 6H), 1.4-1.2(m, 4H). ¹³C { 'H} (75MHz, CDC13): 175.0, 164., 140.4, 139.4, 136.6, 127.0, 125.0, 123.5, 121.1 , 121.0, 1 10.3, 55.4, 42.5, 29.5, 25.6.(75MHz, CDC13):. MALDY-MS im/z): M⁺ calcd for CssL ^Ch, 576.3; found 576.3.

[000183]

Synthesis of DF-I-59-2

[000184] A suspension of DF-I-49 (0.5 g, 0.9 mmol) in phosphoryl trichloride (10 mL) was stirred in reflux overnight and cooled to room temperature. Then phosphoryl trichloride was removed under reduced pressure. The resulting residue was poured into ice-cold water and generated a white precipitate, which was extracted with dichloromethane and dried over sodium sulfate. Upon removal of sodium sulfate and solvent under reduced pressure, the resulting residue was purified by recrystallization from ethyl acetate to give a white powder ( 0.25g, 56%). Ή (300MHz, CDC13): δ 8.35 (s, .l H), 8.04-8.00(m, I H), 7.85-7.81 (m, I H), 7.26- 7.20 (m, I H), 3.04-2.95 (m, I H), 2.20-2.10(m, H), 1.90-1.81 (m, 2H), 1.80-1.62(m, 3H), 1.45-1.21 (m, 3H). ¹³C { ' H} (75MHZ, CDC13): 170.8, 163.2, 140.4, 140.3, 127.7, 126.4, 123.8, 123.6, 120.8, 120.6, 109.5, 35.3, 30.2, 25.5, 25.4. EI-MS (m/z): M⁺ calcd for C₃8H₃oN₄0, 558.2; found 558.2.

Conclusions

[000185] The above specification, examples and data provide exemplary description of the manufacture and use of the various compositions and devices of the inventions, and methods for their manufacture and use. In view of those disclosures, one of ordinary skill in the art will be able to envision many additional embodiments or sub-embodiments of the inventions disclosed and claimed herein to be obvious, and that they can be made without departing from the scope of the inventions disclosed herein. The claims hereinafter appended define some of those embodiments.

Claims

1. A 2-alkyl-5-phenyl-l ,3,4-oxadiazole-carbazole compound having one or more carbazole groups bound to the 5 -phenyl ring, the compound having the formula:

wherein

1 2 3

a) at least one of the R , R and R groups is independently selected from monocarbazole groups, biscarbazole groups, or triscarbazole groups optionally substituted with one or more fluoride, cyano, or a C1-C20 linear or branched alkyl, fluoroalkyl, alkoxide, or

1 2 3

fluoroalkoxide groups; and the remaining R , R" or R^J groups are independently selected from hydrogen, fluoride, cyano, or a C1-C20 linear or branched alkyl, fluoroalkyl, alkoxide, or fluoroalkoxide groups; and

b) R⁴ is selected from a C1-C30 normal, branched, mono-, bi- or tricyclic alkyl optionally substituted with one to five independently selected alkoxide, fluoroalkoxide, aryl, or heteroaryl groups.

The compounds of claim 1 wherein R⁴ is selected from a C1-C30 normal, branched, mono-, bi- or tricyclic alkyl groups.

The compounds of claim 1 wherein the optionally substituted monocarbazole groups, biscarbazole groups, or triscarbazole groups have the structure

wherein Ar is a C1-C12 aryl or heteroaryl ring, R⁵, R⁵ and R⁶, R⁶ are independently selected from hydrogen, fluoride, cyano , and a Ci-C₆ organic group selected from linear and branched alkyls, fluoroalkyls, alkoxides, and fluoroalkoxides, and R⁷ is a C1-C30 linear, branched mono-, bi- or tricyclic alkyl.

1 2 3

4. The compounds of claim 1 wherein one of the R\ R" and R^J groups

comprises an optionally substituted monocarbazole group, and the remaining

1 2 3

R , R or R groups are hydrogen.

5. The compounds of claim 1 having the structure

wherein R⁵, and R⁶ are independently selected from hydrogen, fluoride, cyano , and a Ci-C₆ organic group selected from linear and branched alkyls, fluoroalkyls, alkoxides, and fluoroalkoxides.

1 2 3

6. The compounds of claim 1 wherein one of the R\ R" and R^J groups is an optionally substituted tris-carbazole group having the structure

2

R" or R 3^J groups are hydrogen, and wherein R 5 , R 5' and R⁶, R^6' are independently selected from hydrogen, fluoride, cyano , and a Ci-C₆ organic group selected from linear and branched alkyls, fluoroalkyls, alkoxides, and fluoroalkoxides.

7. The compounds of claim 1 having the structure

The compounds of any one of claims 1-7, wherein R⁵, R⁵ , R⁶, and R⁶ are independently selected from hydrogen and t-butyl.

The compounds of any one of claims 1-7 wherein R⁴ is a C1-C12 normal or branched alkyl group.

The compounds of any one of claims 1-7 wherein R⁴ is a CH₃ group.

The compounds of any one of claims 1-7 wherein R⁴ is a C1-C12 monocyclic, bicyclic or tricyclic alkyl group.

The compounds of any one of claims 1-7 wherein R⁴ comprises a

cyclopentane, a cyclohexane, a bicyclo[2.2.1]heptane, a bicyclo[2.2.2]octane or adamantane group.

13. The compounds of any one of claims 1-7 wherein R⁴ has the structure

14. A device comprising at least one compound of any one of claims 1-7.

15. A device of claim 14 that is a light emitting diode.

16. The device of claim 15 wherein the light emitting diode comprises the following layers:

a) an anode layer,

b) a hole transporting layer,

c) an emission layer,

d) an electron transporting layer, and

e) a cathode layer,

f)

17. The device of claim 16 wherein at least one compound of any of the claims 1-6 is present in the emission layer. compound that emits light when electrical current is passed through the device.

19. The device of claim 18 wherein the guest compound is a metal complex wherein the metal is selected from Re, Ru, Os, Rh, Ir, Pd, Pt, Cu and Au.

20. The device of claim 18 wherein the guest compound is a phosphorescent metal complex wherein the metal is selected from Re, Os, Ir, Pd, Pt, and Au.