ORGANIC ELECTROLUMINESCENT MATERIALS AND DEVICES

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

an anode;

a cathode; and

an organic layer disposed between the anode and the cathode;

wherein the organic layer comprises a first compound as an emitter;

wherein the first compound is selected from the group consisting of phosphorescent emitter and delayed fluorescent emitter;

wherein the device emits a luminescent radiation at room temperature when a voltage is applied across the device;

wherein the luminescent radiation comprises a first radiation component emitted from the first compound; and

wherein the first radiation component has a full width at half maximum equal to or less than 15 nm.

2 . The OLED of claim 1 , wherein the first radiation component has a full width at half maximum equal to or less than 12 nm.

3 . The OLED of claim 1 , wherein the first radiation component has a full width at half maximum equal to or less than 9 nm.

4 . The OLED of claim 1 , wherein the first compound comprises a fused ring structure containing five or more fused rings.

5 . The OLED of claim 4 , wherein the fused ring structure comprises 5-membered and 6-membered rings.

6 . The OLED of claim 1 , wherein the first compound is capable of emitting light from a triplet excited state to a ground singlet state in the device.

7 . The OLED of claim 1 , wherein the first compound is a TADF emitter.

8 . The OLED of claim 1 , wherein the first compound is a metal coordination complex having a metal-carbon bond or a metal-nitrogen bond.

9 . The OLED of claim 8 , wherein the metal is selected from the group consisting of Ir, Rh, Re, Ru, Os, Pt, Pd, Au, Ag, and Cu.

10 . The OLED of claim 9 , wherein the first compound has a first fragment having at least five rings fused next to each other consecutively, wherein the first fragment has at least two atoms coordinated to the metal.

11 . The OLED of claim 10 , wherein the first fragment of the first compound is a ligand L A of Formula I;

wherein:

rings A, B, C, D, and E are each independently a 5-membered or 6-membered carbocyclic or heterocyclic ring;

Z 1 -Z 12 are each independently C or N;

R A , R B , R C , R D , and R E each independently represents zero, mono, or up to a maximum allowed substitutions to its associated ring;

if an R A , R B , R C , R D , or R E represents no substitution, then said R A , R B , R C , R D , or R E is hydrogen;

if R A , R B , R C , R D , or R E represents a substituent, then each R A , R B , R C , R D , and R E is independently a substituent selected from the group consisting of deuterium, halide, alkyl, cycloalkyl, fluorinated alkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, boryl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof;

two substituents can be joined or fused together to form a ring;

wherein the ligand L A is complexed to a metal M at Z 1 and Z 6 ;

wherein the metal M is selected from the group consisting of Ir, Rh, Re, Ru, Os, Pt, Pd, Au, Ag, and Cu;

wherein M can be coordinated to other ligands; and

wherein the ligand L A can be linked with other ligands to form a tridentate, tetradentate, pentadentate, or hexadentate ligand.

12 . The OLED of claim 11 , wherein one of Z 1 and Z 6 is N and the other is C.

13 . The OLED of claim 11 , wherein Z 1 and Z 6 are N

14 . The OLED of claim 11 , wherein Z 1 and Z 6 are C.

15 . The OLED of claim 11 , wherein R A , R B , R C , R D , and R E are each independently selected from the group consisting of deuterium, fluorine, alkyl, cycloalkyl, heteroalkyl, alkoxy, aryloxy, amino, silyl, boryl, alkenyl, cycloalkenyl, heteroalkenyl, aryl, heteroaryl, nitrile, isonitrile, and combinations thereof.

16 . The OLED of claim 11 , wherein the metal is Pt, Ir, or Cu.

17 . The OLED of claim 11 , wherein the at least five rings fused next to each other consecutively comprises two 5-membered rings and three 6-membered rings.

18 . The OLED of claim 11 , wherein the at least five rings fused next to each other consecutively comprises five aromatic rings.