A light emitting device comprising at least one compound of formula (I), (II) or (III) wherein R.sub.1 and R.sub.2, which may be the same or different, are organic substituents not including H, and wherein R.sub.3 and R.sub.5 are each independently selected from halo and organic substituents not including H, and wherein R.sub.4, R.sub.6, R.sub.7, R.sub.8, R.sub.9, and R.sub.10 are each independently selected from H, halo, and organic substituents, wherein any two or more of R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6, R.sub.7, R.sub.8, R.sub.9, and R.sub.10 may optionally be fused together to form a ring system, provided that one of R.sub.3 and R.sub.5 is not part of a fused ring system, and provided that R.sub.1 and R.sub.2 are not fused to each other to form a ring system, and wherein one but not both of either (a) R.sub.3 and R.sub.4, or (b) R.sub.5 and R.sub.6, are fused to each other to form a ring system.