A compound having a structure of Formula 1: is disclosed. In Formula 1, each one of X1 to X16 is independently CR or N; at least two adjacent of X1 to X16 are CR; at least one pair of adjacent Rs is fused to one of the Ring A, Ring B, Ring C, or Ring D; each instance of Y1, Y2, Y3, and Y4 is independently CR1 or N; each instance of Z is independently CR2R3, NR4, O, S or Se; each instance of R, R1, R2, R3, and R4 are independently selected from a variety of substituents; and any adjacent substituents of R, R1, R2, R3, and R4 are optionally joined or fused into a ring. Formulations and devices, such as an OLEDs, that include the compound of Formula 1 are also described.