Organic electroluminescent materials and devices

A composition of materials comprising a first compound, wherein the first compound has a formula:

• wherein G1 is selected from the group consisting of dibenzofuran, dibenzothiophene, dibenzoselenophene, and fluorene;
• wherein L1 is selected from the group consisting of phenyl, biphenyl, terphenyl, pyridine, pyrimidine, and combinations thereof;
• L2 and L3 are each independently selected from the group consisting of direct bond, phenyl, biphenyl, terphenyl, pyridine, pyrimidine, and combinations thereof;
• wherein G4 is selected from the group consisting of phenyl, biphenyl, terphenyl, naphthalene, phenanthrene, pyridine, pyrimidine, pyrazine, quinoline, isoquinoline, phenanthroline, and combinations thereof;
• wherein G2, G3, and G5 are each independently selected from the group consisting of phenyl, biphenyl, terphenyl, fluorene, naphthalene, phenanthrene, pyridine, pyrimidine, pyrazine, quinoline, isoquinoline, phenanthroline, aza-fluorene, and combinations thereof;
• wherein G2, G3, G4, and G5 are each optionally further substituted with one or more unfused substituents selected from the group consisting of deuterium, alkyl, alkoxyl, cycloalkyl, cycloalkoxyl, halogen, nitro, nitrile, silyl, phenyl, biphenyl, terphenyl, pyridine, and combinations thereof;
• wherein m is an integer from 0 to 7,
• wherein n is an integer from 1 to 4;
• wherein, when m or n is larger than 1, each G4 or G5 can be same or different;
• wherein
• if L1 is phenyl, then at least one of the following is true:
• (i) n is 0, (ii) n is 1 and G5 is not biphenyl, (ii) m+n is at least 2.