In certain embodiments, the invention provides boron-nitrogen heterocycles having Formula (I): wherein one of the E1 and E2 is N, and one of the E1 and E2 is B; wherein E3 and E4 is carbon; wherein ring Y and ring Z are 5-membered or 6-membered carbocyclic or heterocyclic aromatic ring fused to ring X; wherein R2 and R3 represent mono, di, tri, tetra substitutions or no substitution; wherein R2 and R3 are each independently selected from various substituents; and wherein any two adjacent R2, and R3 are optionally joined to form a ring, which may be further substituted. In certain embodiments, the invention provides devices, such as organic light emitting devices, that comprise such boron-nitrogen heterocycles.