A compound having a structure of Formula I: Formula I, is disclosed. In the structure of Formula I: X is selected from a group consisting of O, S and Se; G2 and G3 are each independently selected from benzene, biphenyl, fluorene, naphthalene, phenanthrene, triphenylene, dibenzofuran, dibenzothiophene, dibenzoselenophene, pyridine, pyrimidine, quinoline, isoquinoline, phenanthroline, aza-fluorene, and combinations thereof; L is selected from phenyl, biphenyl, terphenyl and pyridine, and combinations thereof; G2, G3 and L are each optionally further substituted with one or more unfused substituents; R1, R2, and each R3, R4, R5 and R6 are an unfused substituent selected from hydrogen, deuterium, alkyl, alkoxyl, cycloalkyl, cycloalkoxyl, halogen, nitro, nitrile, silyl, benzene, biphenyl, terphenyl, pyridine, and combinations thereof; and R1 and R2 are optionally joined to form a ring. Formulations and devices, such as an OLEDs, that include the compound of Formula I, and, optionally a co-host, are also described.