Carbazole modified orthophenylene compounds, 9-([1,1′:2′,1′′-terphenyl]-3-yl)carbazole (Cz-Ter), 9-([1,1′:2′,1′′:2′′,1′′′-quaterphenyl]-3-yl)carbazole (Cz-Quat), 9-([1,1′:2′,1′′:2′′,1′′′:2′′′,1′′′′-quinquephenyl]-3-yl)carbazole (Cz-Quin), were synthesized as host materials for blue phosphorescent organic light emitting diodes. The carbazole modified orthophenylene based host materials showed high triplet energy of above 2.90 eV and there was no reduction of triplet energy according to the increase in the number of phenyl units of the orthophenylene moieties. Cz-Ter, Cz-Quat and Cz-Quin showed maximum quantum efficiencies of 16.2%, 17.3% and 20.9% in blue PHOLEDs, respectively.