A composition of materials comprising a first compound and a second compound, wherein the first compound has the formula: wherein G 1 is selected from the group consisting of dibenzofuran, dibenzothiophene, dibenzoselenophene, and fluorene; wherein L 1, L 2 and L 3 are each independently selected from the group consisting of direct bond, phenyl, biphenyl, terphenyl, pyridine, pyrimidine, and combinations thereof; wherein G 4 is selected from the group consisting of phenyl, biphenyl, terphenyl, naphthalene, phenanthrene, pyridine, pyrimidine, pyrazine, quinoline, isoquinoline, phenanthroline, and combinations thereof; wherein G 2, G 3, and G 5 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 G 2, G 3, G 4, and G 5 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 0 to 4; wherein, when m or n is larger than 1, then each G 4 or G 5 can be same or different; wherein, when n is 0, and m is equal to or greater than 1, then each G 4 is selected from the group consisting of phenyl, and biphenyl; wherein, when n is equal to or greater than 1, then L 1 is not a direct bond; and wherein, when m and n are both 0, then L 1 is biphenyl, and wherein the second compound has the formula II: wherein Ar 1 is selected from the group consisting of triphenylene, and aza-triphenylene; wherein Ar 2 is selected from the group consisting of a direct bond, phenyl, biphenyl, terphenyl, naphthalene, pyridine, dibenzofuran, dibenzothiophene, dibenzoselenophene, aza-dibenzofuran, aza-dibenzothiophene, aza-dibenzoselenophene, and combinations thereof; wherein Ar 3 is selected from the group consisting of benzene, biphenyl, terphenyl, naphthalene, pyridine, dibenzofuran, dibenzothiophene, dibenzoselenophene, aza-dibenzofuran, aza-dibenzothiophene, aza-dibenzoselenophene, carbazole, aza-carbazole, and combinations thereof; and wherein Ar 1, Ar 2 and Ar 3 are each, independently, optionally further substituted with one or more substitutions selected from the group consisting of deuterium, halogen, alkyl, aryl, heteroaryl, and combinations thereof. wherein G 1 is selected from the group consisting of dibenzofuran, dibenzothiophene, dibenzoselenophene, and fluorene; wherein L 1, L 2 and L 3 are each independently selected from the group consisting of direct bond, phenyl, biphenyl, terphenyl, pyridine, pyrimidine, and combinations thereof; wherein G 4 is selected from the group consisting of phenyl, biphenyl, terphenyl, naphthalene, phenanthrene, pyridine, pyrimidine, pyrazine, quinoline, isoquinoline, phenanthroline, and combinations thereof; wherein G 2, G 3, and G 5 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 G 2, G 3, G 4, and G 5 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 0 to 4; wherein, when m or n is larger than 1, then each G 4 or G 5 can be same or different; wherein, when n is 0, and m is equal to or greater than 1, then each G 4 is selected from the group consisting of phenyl, and biphenyl; wherein, when n is equal to or greater than 1, then L 1 is not a direct bond; and wherein, when m and n are both 0, then L 1 is biphenyl, and wherein the second compound has the formula II: wherein Ar 1 is selected from the group consisting of triphenylene, and aza-triphenylene; wherein Ar 2 is selected from the group consisting of a direct bond, phenyl, biphenyl, terphenyl, naphthalene, pyridine, dibenzofuran, dibenzothiophene, dibenzoselenophene, aza-dibenzofuran, aza-dibenzothiophene, aza-dibenzoselenophene, and combinations thereof; wherein Ar 3 is selected from the group consisting of benzene, biphenyl, terphenyl, naphthalene, pyridine, dibenzofuran, dibenzothiophene, dibenzoselenophene, aza-dibenzofuran, aza-dibenzothiophene, aza-dibenzoselenophene, carbazole, aza-carbazole, and combinations thereof; and wherein Ar 1, Ar 2 and Ar 3 are each, independently, optionally further substituted with one or more substitutions selected from the group consisting of deuterium, halogen, alkyl, aryl, heteroaryl, and combinations thereof.