Organic electroluminescent materials and devices

1. A compound having a metal coordination complex structure;

wherein the compound is capable of functioning as an emitter in an organic light emitting device at room temperature;

wherein when there are more than one ligand in the compound each ligand is different from each other;

wherein the compound has the formula of M(L 1 )(L 2 )(L 3 ) and L 1 , L 2 , and L 3 are different from each other;

wherein each of L 1 , L 2 , and L 3 is a ligand having at least two six-membered rings bridged together, wherein two adjacent bridged six-membered rings are each coordinated to the metal, and at least one of the two bridged six-membered rings having at least one nitrogen atom,

wherein the compound has a first substituent R 1 at one of the ligands' periphery;

wherein a first distance is the distance between the metal and an atom in R 1 that is the farthest away from the metal;

wherein the first distance is longer than any distance between the metal and any other atoms in the compound; and

wherein when a sphere having a radius r is defined whose center is the metal and the radius r is the smallest radius that will allow the sphere to enclose all atoms in the compound that are not part of R 1 , the first distance is longer than the radius r by at least 2.9 Å.

2. The compound of claim 1 , wherein the compound has a second substituent R 2 at one of the ligands' periphery;

wherein a second distance is the distance between the metal and an atom in R 2 that is the farthest away from the metal; and

wherein when the radius r is the smallest radius that will allow the sphere to enclose all atoms in the compound that are not part of R 1 or R 2 , the second distance is longer than r by at least 1.5 Å.

3. The compound of claim 2 , wherein R 1 and R 2 are on different ligands.

4. The compound of claim 2 , wherein the first and second distances are all longer than r by at least 4.3 Å.

5. The compound of claim 2 , wherein R 1 is attached to an aromatic ring having a first coordination atom, R 2 is attached to an aromatic ring having a second coordination atom; and

wherein the first coordination atom is in a trans configuration to the second coordination atom relative to the metal.

6. The compound of claim 2 , wherein the compound has a third substituent R 3 at one of the ligands' periphery;

wherein a third distance is the distance between the metal and an atom in R 3 that is the farthest away from the metal; and

wherein when the radius r is the smallest radius that will allow the sphere to enclose all atoms in the compound that are not part of R 1 , R 2 , or R 3 , the third distance is longer than r by at least 1.5 Å.

7. The compound of claim 6 , wherein R 1 , R 2 , and R 3 are on different ligands;

wherein the compound has an octahedral coordination geometry with three bidentate ligands, wherein each of the three bidentate ligands having two coordination atoms and a midpoint defined between the two coordination atoms;

wherein the three midpoints define a first plane; and

wherein each atom in R 1 , R 2 , and R 3 have a point-to-plane distance less than 5 Å relative to the first plane.

8. The compound of claim 7 , wherein any atom in R 1 , R 2 , and R 3 has a point-to-plane distance less than r relative to the first plane.

9. The compound of claim 1 , wherein the compound has a transition dipole moment axis; and

wherein an angle between the transition dipole moment axis and an axis along the first distance is less than 40°.

10. The compound of claim 1 , wherein the triplet energy of a first homoleptic metal complex, whose ligands are same as the ligand in the compound having R 1 , is lower than the triplet energy of a second homoleptic metal complex, whose ligands are any of the other ligands in the compound, by at least 0.05 eV.

11. The compound of claim 1 , wherein the compound is capable of functioning as a phosphorescent emitter, a fluorescent emitter, or a delayed fluorescent emitter in an organic light emitting device at room temperature.

12. The compound of claim 1 , wherein the compound comprises a first benzene ring coordinated to the metal; and wherein the first benzene ring is fused by a second aromatic ring.

13. The compound of claim 1 , wherein the compound has the formula of M(L 1 ) x (L 2 ) y (L 3 ) z ;

wherein x is 1, 2, or 3;

wherein y is 0, 1, or 2;

wherein z is 0, 1, or 2;

wherein x+y+z is the oxidation state of the metal M;

wherein L 1 , L 2 , and L 3 are each independently selected from the group consisting of:

wherein each X 1 to X 17 are independently selected from the group consisting of carbon and nitrogen;

wherein Z 1 , Z 2 , and Z 3 are independently selected from the group consisting of carbon and nitrogen;

wherein X is selected from the group consisting of BR′, NR′, PR′, O, S, Se, C═O, S═O, SO 2 , CR′R″, SiR′R″, and GeR′R″;

wherein R′ and R″ are optionally fused or joined to form a ring;

wherein each R a , R b , R c , and R d may represent from mono substitution to the possible maximum number of substitution, or no substitution;

wherein R′, R″, R a , R b , R c , and R d are each independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; and

wherein any two R a , R b , R c , and R d are optionally fused or joined to form a ring or form a multidentate ligand; and

wherein at least one of the R a , R b , R c , and R d includes R 1 .

14. The compound of claim 13 , wherein at least one pair of substituents R a , R b , R c , and R d within the same ring are joined and fused into a ring.

15. The compound of claim 13 , wherein at least one pair of substituents R a , R b , R c , and R d between two nearby rings are joined and fused into a ring.

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

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

18. The compound of claim 1 , wherein the metal is selected from the group consisting of Ir, Rh, Re, Ru, Os, Pt, Pd, Au, Ag, and Cu.

19. An organic light emitting device (OLED) comprising:

an anode;

a cathode; and

an organic layer, disposed between the anode and the cathode, comprising a compound having a metal coordination complex structure;

wherein the compound is capable of functioning as an emitter in an organic light emitting device at room temperature;

wherein the compound has the formula of M(L 1 )(L 2 )(L 3 ) and L 1 , L 2 , and L 3 are different from each other;

wherein each of L 1 , L 2 , and L 3 is a ligand having at least two six-membered rings bridged together, wherein two adjacent bridged six-membered rings are each coordinated to the metal, and at least one of the two bridged six-membered rings having at least one nitrogen atom,

wherein the compound has a first substituent R 1 at one of the ligands' periphery;

wherein a first distance is the distance between the metal and an atom in R 1 that is the farthest away from the metal;

wherein the first distance is longer than any distance between the metal and any other atoms in the compound; and

wherein when a sphere having a radius r is defined whose center is the metal and the radius r is the smallest radius that will allow the sphere to enclose all atoms in the compound that are not part of R 1 , the first distance is longer than the radius r by at least 2.9 Å.

20. The OLED of claim 19 , wherein the metal is selected from the group consisting of Ir, Rh, Re, Ru, Os, Pt, Pd, Au, Ag, and Cu.

21. A consumer product comprising an organic light-emitting device (OLED) comprising:

an anode;

a cathode; and

an organic layer, disposed between the anode and the cathode, comprising a compound having a metal coordination complex structure;

wherein the compound is capable of functioning as an emitter in an organic light emitting device at room temperature;

wherein the compound has the formula of M(L 1 )(L 2 )(L 3 ) and L 1 , L 2 , and L 3 are different from each other;

wherein each of L 1 , L 2 , and L 3 is a ligand having at least two six-membered rings bridged together, wherein two adjacent bridged six-membered rings are each coordinated to the metal, and at least one of the two bridged six-membered rings having at least one nitrogen atom,

wherein the compound has a first substituent R 1 at one of the ligands' periphery;

wherein a first distance is the distance between the metal and an atom in R 1 that is the farthest away from the metal;

wherein the first distance is longer than any distance between the metal and any other atoms in the compound; and

wherein when a sphere having a radius r is defined whose center is the metal and the radius r is the smallest radius that will allow the sphere to enclose all atoms in the compound that are not part of R 1 , the first distance is longer than the radius r by at least 2.9 Å.

22. The consumer product of claim 21 , wherein the metal is selected from the group consisting of Ir, Rh, Re, Ru, Os, Pt, Pd, Au, Ag, and Cu.

23. The consumer product of claim 21 , wherein the consumer product is selected from the group consisting of a flat panel display, a computer monitor, a medical monitors television, a billboard, a light for interior or exterior illumination and/or signaling, a heads-up display, a fully or partially transparent display, a flexible display, a laser printer, a telephone, a cell phone, tablet, a phablet, a personal digital assistant (PDA), a wearable device, a laptop computer, a digital camera, a camcorder, a viewfinder, a micro-display, a 3-D display, a virtual reality or augmented reality display, a vehicle, a large area wall, a theater or stadium screen, and a sign.