A light emitting device comprising at least one compound of formula (I), (II) or (III) wherein R1 and R2, which may be the same or different, are organic substituents not including H, and wherein R3 and R5 are each independently selected from halo and organic substituents not including H, and wherein R4, R6, R7, R8, R9, and R10 are each independently selected from H, halo, and organic substituents, wherein any two or more of R1, R2, R3, R4, R5, R6, R7, R8, R9, and R10 may optionally be fused together to form a ring system, provided that one of R3 and R5 is not part of a fused ring system, and provided that R1 and R2 are not fused to each other to form a ring system, and wherein one but not both of either (a) R3 and R4, or (b) R5 and R6, are fused to each other to form a ring system.