A six-coordinated ruthenium complex is represented by the following formula (I):
RuL1L2L3 (I)
wherein L1 represents a 2,2′-bipyridine-based bidentate ligand having at least two functional groups selected from COOH, a carboxylate group and the combination thereof; and L2 and L3 independently represent a 1-(haloalkylpyrazole)-isoquinoline-based bidentate ligand of formula (II) or formula (III).