There is disclosed herein phosphorescent compounds, uses thereof, and devices including organic light emitting diode (OLEDs) including such compounds.Compounds of interest include: wherein A is Os or Ru The anionic chelating chromophores N^N, which are formed by connecting one pentagonal ring structure containing at least two nitrogen atoms to a hexagonal pyridine type of fragment via a direct carbon-carbon linkage.L is a neutral donor ligand; the typical example includes carbonyl, pyridine, phosphine, arsine and isocyanide; two neutral L's can also combine to produce the so-called chelating ligand such as 2,2′-bipyridine, 1,10-phenanthroline and N-heterocyclic carbene (NHC) ligand, or bidentate phosphorous ligands such as 1,2-bis(diphenylphosphino)ethane, 1,2-bis(diphenylphosphino)benzene.L can occupy either cis or trans orientation.When L occupies the trans position, the preferred structure contains both the hexagonal fragment of N^N as well as its pentagonal fragment located at the trans position respect to their counterparts of the second N^N chromophore.When L occupies the cis position, the preferred structure consists of the pentagonal unit of N^N chromophores residing opposite to the L. X,1 X2 and X3 independently are C or N; when X2 is N, R1 is omitted, when X3 is N, R2 is omitted, R1 is H, C1-C8 alkyl, C1-C8 substituted phenyl or C1-C4 perfluoroalkyl, R2 is H, F or cyano substituent, X4 is either C or N; X4 may locate at any position of the hexagonal ring, when X4 is N and R3 and R4 are not linked to X4, R3 is H, methyl or C1-C3 small alkyl, R4 is H, methyl or C1-C3 small alkyl, or R3 and R4 together form an additional conjugated unit with structure