US Patent Application for ORGANIC ELECTROLUMINESCENT MATERIALS AND DEVICES Patent Application (Application #20210098717 issued April 1, 2021) (2024)

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Application No. 62/906,305, filed on Sep. 26, 2019, and U.S. Provisional Application No. 63/010,815, filed on Apr. 16, 2020, the entire contents of which are incorporated herein by reference.

FIELD

The present disclosure generally relates to organometallic compounds and formulations and their various uses including as emitters in devices such as organic light emitting diodes and related electronic devices.

BACKGROUND

Opto-electronic devices that make use of organic materials are becoming increasingly desirable for various 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 diodes/devices (OLEDs), organic phototransistors, organic photovoltaic cells, and organic photodetectors. For OLEDs, the organic materials may have performance advantages over conventional materials.

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.

One application for phosphorescent emissive molecules is a full color display. Industry standards for such a display call for pixels adapted to emit particular colors, referred to as “saturated” colors. In particular, these standards call for saturated red, green, and blue pixels. Alternatively, the OLED can be designed to emit white light. In conventional liquid crystal displays emission from a white backlight is filtered using absorption filters to produce red, green and blue emission. The same technique can also be used with OLEDs. The white OLED can be either a single emissive layer (EML) device or a stack structure. Color may be measured using CIE coordinates, which are well known to the art.

SUMMARY

In one aspect, the present disclosure provides a compound comprising a first ligand L_A of Formula I

In Formula I:

ring B is a 5-membered or 6-membered carbocyclic or heterocyclic ring, which can be further fused;

X¹, X², and X³ are each independently CR^A or N;

R is a 5-membered or 6-membered carbocyclic or heterocyclic ring, which can be further fused or substituted;

provided that

(1) when ring B is an unfused 6-membered ring, X¹ and X² are N, and X³ is C;

(2) when ring B is a fused 6-membered ring, ring B has the structure of Formula II,

where:

the wavy line indicates the point of connection to ring A;

• • Q¹, Q², Q³, Q⁴, Q⁵, and Q⁶ are each independently C or N; and

when proviso (2) applies, at least one of the following conditions is true:

• • (I) at least one of X¹, X², and X³ is N; or
  • (II) R is two or more fused or unfused 5-membered or 6-membered carbocyclic or heterocyclic rings, which can be further fused or substituted;

R^B and R^C each independently represent mono to the maximum number of allowable substitutions, or no substitution;

each R^A, R^B, and R^C is independently a hydrogen or a substituent selected from the group consisting of the general substituents disclosed herein, and combinations thereof;

L_A is coordinated to a metal M through the indicated dashed lines;

M is selected from the group consisting of Ir, Os, Pt, Pd, Cu, Ag, and Au;

M can be coordinated to other ligands;

L_A can join with other ligands to comprise a tridentate, tetradentate, pentadentate, or hexadentate ligand; and

any two substituents can be joined or fused to form a ring.

In another aspect, the present disclosure provides a formulation of the compound of the present disclosure.

In yet another aspect, the present disclosure provides an OLED having an organic layer comprising the compound of the present disclosure.

In yet another aspect, the present disclosure provides a consumer product comprising an OLED with an organic layer comprising the compound of the present disclosure.

DETAILED DESCRIPTION A. Terminology

Unless otherwise specified, the below terms used herein are defined as follows:

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 circ*mstances. 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 a 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.

As used herein, “top” means furthest away from the substrate, while “bottom” means closest to 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 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 processable” means capable of being dissolved, dispersed, or transported in and/or deposited from a liquid medium, either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed that the ligand directly contributes to the photoactive properties of an emissive material. A ligand may be referred to as “ancillary” when it is believed that the ligand does not contribute to the photoactive properties of an emissive material, although an ancillary ligand may alter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled in the art, a first “Highest Occupied Molecular Orbital” (hom*o) or “Lowest Unoccupied Molecular Orbital” (LUMO) energy level is “greater than” or “higher than” a second hom*o or LUMO energy level if the first energy level is closer to the vacuum energy level. Since ionization potentials (IP) are measured as a negative energy relative to a vacuum level, a higher hom*o energy level corresponds to an IP having a smaller absolute value (an IP that is less negative). Similarly, a higher LUMO energy level corresponds to an electron affinity (EA) having a smaller absolute value (an EA that is less negative). On a conventional energy level diagram, with the vacuum level at the top, the LUMO energy level of a material is higher than the hom*o energy level of the same material. A “higher” hom*o or LUMO energy level appears closer to the top of such a diagram than a “lower” hom*o or LUMO energy level.

As used herein, and as would be generally understood by one skilled in the art, a first work function is “greater than” or “higher than” a second work function if the first work function has a higher absolute value. Because work functions are generally measured as negative numbers relative to vacuum level, this means that a “higher” work function is more negative. On a conventional energy level diagram, with the vacuum level at the top, a “higher” work function is illustrated as further away from the vacuum level in the downward direction. Thus, the definitions of hom*o and LUMO energy levels follow a different convention than work functions.

The terms “halo,” “halogen,” and “halide” are used interchangeably and refer to fluorine, chlorine, bromine, and iodine.

The term “acyl” refers to a substituted carbonyl radical (C(O)—R_s).

The term “ester” refers to a substituted oxycarbonyl (—O—C(O)—R_s or —C(O)—O—R_s) radical.

The term “ether” refers to an —OR_s radical.

The terms “sulfanyl” or “thio-ether” are used interchangeably and refer to a —SR_s radical.

The term “sulfinyl” refers to a —S(O)—R_s radical.

The term “sulfonyl” refers to a —SO₂—R_s radical.

The term “phosphino” refers to a —P(R_s)₃ radical, wherein each R_s can be same or different.

The term “silyl” refers to a —Si(R_s)₃ radical, wherein each R_s can be same or different.

The term “boryl” refers to a —B(R_s)₂ radical or its Lewis adduct —B(R_s)₃ radical, wherein R_s can be same or different.

In each of the above, R_s can be hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, and combination thereof. Preferred R_s is selected from the group consisting of alkyl, cycloalkyl, aryl, heteroaryl, and combination thereof.

The term “alkyl” refers to and includes both straight and branched chain alkyl radicals. Preferred alkyl groups are those containing from one to fifteen carbon atoms and includes methyl, ethyl, propyl, 1-methylethyl, butyl, 1-methylpropyl, 2-methylpropyl, pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, and the like. Additionally, the alkyl group may be optionally substituted.

The term “cycloalkyl” refers to and includes monocyclic, polycyclic, and spiro alkyl radicals. Preferred cycloalkyl groups are those containing 3 to 12 ring carbon atoms and includes cyclopropyl, cyclopentyl, cyclohexyl, bicyclo[3.1.1]heptyl, spiro[4.5]decyl, spiro[5.5]undecyl, adamantyl, and the like. Additionally, the cycloalkyl group may be optionally substituted.

The terms “heteroalkyl” or “heterocycloalkyl” refer to an alkyl or a cycloalkyl radical, respectively, having at least one carbon atom replaced by a heteroatom. Optionally the at least one heteroatom is selected from O, S, N, P, B, Si and Se, preferably, O, S or N. Additionally, the heteroalkyl or heterocycloalkyl group may be optionally substituted.

The term “alkenyl” refers to and includes both straight and branched chain alkene radicals. Alkenyl groups are essentially alkyl groups that include at least one carbon-carbon double bond in the alkyl chain. Cycloalkenyl groups are essentially cycloalkyl groups that include at least one carbon-carbon double bond in the cycloalkyl ring. The term “heteroalkenyl” as used herein refers to an alkenyl radical having at least one carbon atom replaced by a heteroatom. Optionally the at least one heteroatom is selected from O, S, N, P, B, Si, and Se, preferably, O, S, or N. Preferred alkenyl, cycloalkenyl, or heteroalkenyl groups are those containing two to fifteen carbon atoms. Additionally, the alkenyl, cycloalkenyl, or heteroalkenyl group may be optionally substituted.

The term “alkynyl” refers to and includes both straight and branched chain alkyne radicals. Alkynyl groups are essentially alkyl groups that include at least one carbon-carbon triple bond in the alkyl chain. Preferred alkynyl groups are those containing two to fifteen carbon atoms. Additionally, the alkynyl group may be optionally substituted.

The terms “aralkyl” or “arylalkyl” are used interchangeably and refer to an alkyl group that is substituted with an aryl group. Additionally, the aralkyl group may be optionally substituted.

The term “heterocyclic group” refers to and includes aromatic and non-aromatic cyclic radicals containing at least one heteroatom. Optionally the at least one heteroatom is selected from O, S, N, P, B, Si, and Se, preferably, O, S, or N. Hetero-aromatic cyclic radicals may be used interchangeably with heteroaryl. Preferred hetero-non-aromatic cyclic groups are those containing 3 to 7 ring atoms which includes at least one hetero atom, and includes cyclic amines such as morpholino, piperidino, pyrrolidino, and the like, and cyclic ethers/thio-ethers, such as tetrahydrofuran, tetrahydropyran, tetrahydrothiophene, and the like. Additionally, the heterocyclic group may be optionally substituted.

The term “aryl” refers to and includes both single-ring aromatic hydrocarbyl groups and polycyclic aromatic ring systems. The polycyclic rings may have two or more rings in which two carbons are common to two adjoining rings (the rings are “fused”) wherein at least one of the rings is an aromatic hydrocarbyl group, e.g., the other rings can be cycloalkyls, cycloalkenyls, aryl, heterocycles, and/or heteroaryls. Preferred aryl groups are those containing six to thirty carbon atoms, preferably six to twenty carbon atoms, more preferably six to twelve carbon atoms. Especially preferred is an aryl group having six carbons, ten carbons or twelve carbons. Suitable aryl groups include phenyl, biphenyl, triphenyl, triphenylene, tetraphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, and azulene, preferably phenyl, biphenyl, triphenyl, triphenylene, fluorene, and naphthalene. Additionally, the aryl group may be optionally substituted.

The term “heteroaryl” refers to and includes both single-ring aromatic groups and polycyclic aromatic ring systems that include at least one heteroatom. The heteroatoms include, but are not limited to O, S, N, P, B, Si, and Se. In many instances, O, S, or N are the preferred heteroatoms. Hetero-single ring aromatic systems are preferably single rings with 5 or 6 ring atoms, and the ring can have from one to six heteroatoms. The hetero-polycyclic ring systems can have 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. The hetero-polycyclic aromatic ring systems can have from one to six heteroatoms per ring of the polycyclic aromatic ring system. Preferred heteroaryl groups are those containing three to thirty carbon atoms, preferably three to twenty carbon atoms, more preferably three to twelve carbon atoms. Suitable heteroaryl groups include dibenzothiophene, dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene, benzoselenophene, carbazole, indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine, thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine, preferably dibenzothiophene, dibenzofuran, dibenzoselenophene, carbazole, indolocarbazole, imidazole, pyridine, triazine, benzimidazole, 1,2-azaborine, 1,3-azaborine, 1,4-azaborine, borazine, and aza-analogs thereof. Additionally, the heteroaryl group may be optionally substituted.

Of the aryl and heteroaryl groups listed above, the groups of triphenylene, naphthalene, anthracene, dibenzothiophene, dibenzofuran, dibenzoselenophene, carbazole, indolocarbazole, imidazole, pyridine, pyrazine, pyrimidine, triazine, and benzimidazole, and the respective aza-analogs of each thereof are of particular interest.

The terms alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aralkyl, heterocyclic group, aryl, and heteroaryl, as used herein, are independently unsubstituted, or independently substituted, with one or more general substituents.

In many instances, the general substituents are selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, boryl, and combinations thereof.

In some instances, the preferred general substituents are selected from the group consisting of deuterium, fluorine, alkyl, cycloalkyl, heteroalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, aryl, heteroaryl, nitrile, isonitrile, sulfanyl, boryl, and combinations thereof.

In some instances, the more preferred general substituents are selected from the group consisting of deuterium, fluorine, alkyl, cycloalkyl, alkoxy, aryloxy, amino, silyl, boryl, aryl, heteroaryl, sulfanyl, and combinations thereof.

In yet other instances, the most preferred general substituents are selected from the group consisting of deuterium, fluorine, alkyl, cycloalkyl, aryl, heteroaryl, and combinations thereof.

The terms “substituted” and “substitution” refer to a substituent other than H that is bonded to the relevant position, e.g., a carbon or nitrogen. For example, when R¹ represents mono-substitution, then one R¹ must be other than H (i.e., a substitution). Similarly, when R¹ represents di-substitution, then two of R¹ must be other than H. Similarly, when R¹ represents zero or no substitution, R¹, for example, can be a hydrogen for available valencies of ring atoms, as in carbon atoms for benzene and the nitrogen atom in pyrrole, or simply represents nothing for ring atoms with fully filled valencies, e.g., the nitrogen atom in pyridine. The maximum number of substitutions possible in a ring structure will depend on the total number of available valencies in the ring atoms.

As used herein, “combinations thereof” indicates that one or more members of the applicable list are combined to form a known or chemically stable arrangement that one of ordinary skill in the art can envision from the applicable list. For example, an alkyl and deuterium can be combined to form a partial or fully deuterated alkyl group; a halogen and alkyl can be combined to form a halogenated alkyl substituent; and a halogen, alkyl, and aryl can be combined to form a halogenated arylalkyl. In one instance, the term substitution includes a combination of two to four of the listed groups. In another instance, the term substitution includes a combination of two to three groups. In yet another instance, the term substitution includes a combination of two groups. Preferred combinations of substituent groups are those that contain up to fifty atoms that are not hydrogen or deuterium, or those which include up to forty atoms that are not hydrogen or deuterium, or those that include up to thirty atoms that are not hydrogen or deuterium. In many instances, a preferred combination of substituent groups will include up to twenty atoms that are not hydrogen or deuterium.

The “aza” designation in the fragments described herein, i.e. aza-dibenzofuran, aza-dibenzothiophene, etc. means that one or more of the C—H groups in the respective aromatic ring can be replaced by a nitrogen atom, for example, and without any limitation, azatriphenylene encompasses both dibenzo[fh]quinoxaline and dibenzo[fh]quinoline. One of ordinary skill in the art can readily envision other nitrogen analogs of the aza-derivatives described above, and all such analogs are intended to be encompassed by the terms as set forth herein.

As used herein, “deuterium” refers to an isotope of hydrogen. Deuterated compounds can be readily prepared using methods known in the art. For example, U.S. Pat. No. 8,557,400, Patent Pub. No. WO 2006/095951, and U.S. Pat. Application Pub. No. US 2011/0037057, which are hereby incorporated by reference in their entireties, describe the making of deuterium-substituted organometallic complexes. Further reference is made to Ming Yan, et al., Tetrahedron 2015, 71, 1425-30 and Atzrodt et al., Angew. Chem. Int. Ed. (Reviews) 2007, 46, 7744-65, which are incorporated by reference in their entireties, describe the deuteration of the methylene hydrogens in benzyl amines and efficient pathways to replace aromatic ring hydrogens with deuterium, respectively.

It is to be understood that when a molecular fragment is described as being a substituent or otherwise attached to another moiety, its name may be written as if it were a fragment (e.g. phenyl, phenylene, naphthyl, dibenzofuryl) or as if it were the whole molecule (e.g. benzene, naphthalene, dibenzofuran). As used herein, these different ways of designating a substituent or attached fragment are considered to be equivalent.

In some instance, a pair of adjacent substituents can be optionally joined or fused into a ring. The preferred ring is a five, six, or seven-membered carbocyclic or heterocyclic ring, includes both instances where the portion of the ring formed by the pair of substituents is saturated and where the portion of the ring formed by the pair of substituents is unsaturated. As used herein, “adjacent” means that the two substituents involved can be on the same ring next to each other, or on two neighboring rings having the two closest available substitutable positions, such as 2, 2′ positions in a biphenyl, or 1, 8 position in a naphthalene, as long as they can form a stable fused ring system.

B. The Compounds of the Present Disclosure

In one aspect, the present disclosure provides a compound comprising a first ligand L_A of Formula I

In Formula I:

ring B is a 5-membered or 6-membered carbocyclic or heterocyclic ring, which can be further fused;

X¹, X², and X³ are each independently CR^A or N;

R is a 5-membered or 6-membered carbocyclic or heterocyclic ring, which can be further fused or substituted;

provided that

(1) when ring B is an unfused 6-membered ring, X¹ and X² are N, and X³ is C;

(2) when ring B is a fused 6-membered ring, ring B has the structure of Formula II,

where:

the wavy line indicates the point of connection to ring A;

Q¹, Q², Q³, Q⁴, Q⁵, and Q⁶ are each independently C or N; and

when proviso (2) applies, at least one of the following conditions is true:

• • (I) at least one of X¹, X², and X³ is N; or
  • (II) R is two or more fused or unfused 5-membered or 6-membered carbocyclic or heterocyclic rings, which can be further fused or substituted;

R^B and R^C each independently represent mono to the maximum number of allowable substitutions, or no substitution;

each R^A, R^B, and R^C is independently a hydrogen or a substituent selected from the group consisting of the general substituents disclosed herein, and combinations thereof;

L_A is coordinated to a metal M through the indicated dashed lines;

M is selected from the group consisting of Ir, Os, Pt, Pd, Cu, Ag, and Au;

M can be coordinated to other ligands;

L_A can join with other ligands to comprise a tridentate, tetradentate, pentadentate, or hexadentate ligand; and

any two substituents can be joined or fused to form a ring.

In some embodiments, each R^A, R^B, and R^C is independently a hydrogen or a substituent selected from the group consisting of the preferred general substituents disclosed herein, and combinations thereof. In some embodiments, each R^A, R^B, and R^C is independently a hydrogen or a substituent selected from the group consisting of the more preferred general substituents disclosed herein, and combinations thereof.

In some embodiments, M is Ir. In some embodiments, M is Pt.

In some embodiments, X¹ and X² are N, and X³ is C. In some embodiments, X¹ is N, and X² and X³ are C. In some embodiments, X¹ and X³ are N, and X² is C. In some embodiments, X¹ and X³ are C, and X² is N.

In some embodiments, R is a substituted or unsubstituted 6-membered aryl or heteroaryl ring. In some embodiments, R is a substituted or unsubstituted 5-membered heteroaryl ring.

In some embodiments, R is a substituted or unsubstituted cyclohexyl ring. In some embodiments, R is a substituted or unsubstituted cyclopentyl ring. In some embodiments, R is selected from the group consisting of imidazole, oxazole, thiazole, pyridine, phenyl, biphenyl, carbazole, benzofuran, benzothiophene, dibenzofuran, and dibenzothiophene.

In some embodiments, R is two or more fused 5-membered or 6-membered carbocyclic or heterocyclic rings, which can be further fused or substituted. In some embodiments, R is two or more unfused 5-membered or 6-membered carbocyclic or heterocyclic rings, which can be further substituted. In some embodiments, R is two or more fused 5-membered or 6-membered aryl or heteroaryl rings, which can be further fused or substituted. In some embodiments, R is two or more unfused 5-membered or 6-membered aryl or heteroaryl rings, which can be further substituted.

In some embodiments, Ring B has the structure of Formula II, and each of Q¹, Q², Q³, Q⁴, Q⁵, and Q⁶ is C. In some embodiments, Ring B has the structure of Formula II, and at least one of Q¹, Q², Q³, Q⁴, Q⁵, and Q⁶ is N.

In some embodiments, Ring B is selected from the group consisting of phenyl, pyridine, pyrazine, pyridazine, pyrimidine, triazine, furan, thiophene, pyrrole, imidazole, oxazole, and thiazole. In some embodiments, Ring B is a 5-membered ring. In some embodiments, Ring B is a fused 5-membered ring

In some embodiments, the compound comprises at least one substituted or unsubstituted phenylpyridine ligand. In some embodiments, the compound comprises at least one substituted or unsubstituted acetyl-acetonate ligand.

In some embodiments, the compound is heteroleptic. In some embodiments, the compound is hom*oleptic. In some embodiments, the compound is neutral.

In some embodiments, L_A has a structure selected from the group consisting of

In some embodiments, Ring B has a structure selected from the group consisting of:

wherein n is an integer from 1 to 480 and, for each n, substituents R^D, R^E, R^F, and R^G are selected as follows:

In some embodiments, R in Formula I has a structure selected from the group consisting of

which can be further substituted;
where:

each Y is independently selected from the group consisting of S, O, NR^Cy1, CR^Cy2R^Cy3, and SiR^Cy4R^Cy5;

each Q is independently CR^Cy or N; and

each of R^Cy, R^Cy1, R^Cy2, R^Cy3, R^Cy4, and R^Cy5 is independently a hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, boryl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In some embodiments, at least one of X¹, X², and X³ is N, and R has the structure of

In some such embodiments, R^Cy is selected from the group consisting of halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, aryl, heteroaryl, partially or fully deutereated variants thereof, partially or fully fluorinated variants thereof, and combinations thereof.

In some embodiments, the ligand L_A is selected from the group consisting of L_A1-1 to L_A3600-344 defined as follows:

wherein i is an integer from 1 to 3600 and, for each L_Ai-m, R^H, R^I, and G are defined as follows: