A dinuclear Ru(ii) complex of [(bpy)2Ru(H2ipaip)Ru(bpy)2]Cl4 {bpy = 2,2'-bipyridine, H2ipaip = 2-(9-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)anthracen-10-yl)-1H-imidazo[4,5-f][1,10]phenanthroline} is newly synthesized and characterized. Singlet oxygen sensing and ground- and excited-state acid-base properties of this complex are studied. The results indicated that the complex acted as a highly sensitive and selective luminescent probe for singlet oxygen (1O2) in neutral and alkaline aqueous media under visible light excitation at 458 nm, resulting in 5.2- and 7.6-fold emission enhancement, respectively. This probe has advantages of visible light excitation, low singlet oxygen detection limits of 2.7-3.1 nM and high water solubility, thus holding great potential for applications in biological systems.