Near-IR-emitting and/or efficiently photodynamic water-soluble Ru(II) complexes that hold great application potentials as photodynamic therapy and/or photodetection agents for cancers have been poorly explored. In this paper, the solvatochromism, calf thymus DNA binding, and singlet oxygen generation properties of a known ruthenium-(II) complex of visible-emitting [Ru(bpy)(2)(dtdpq)](ClO4)(2) (Ru1) and a new homoleptic complex of near-IR-emitting [Ru(dtdpq)(3)](ClO4)(2) (Ru2) (bpy = 2,2'-bipyridine, dtdpq = 2,3-bis(thiophen-2-yl)pyrazino[2,3-f]-[1,10]phenanothroline) in water are reported. Moreover, DNA photo-cleavage, singlet oxygen generation in HeLa cells, cellular uptake/localization, and in vitro photodynamic therapy for cancer cells of water-soluble Ru1 are described in detail. The results show that Ru1 acted as potent photodynamic cancer therapy and mitochondrial imaging agents. Ru2 exhibited very strong solvatochromism from a visible emission maximum at 588 nm in CH2Cl2 to the near-IR region at 700 nm in water and singlet oxygen generation yield in water (23%) and DNA binding properties (intercalative DNA binding constant on the order of 10(6) M-1) comparable to those of Ru1, which should make Ru2 attractive for the aforementioned applications of Ru1 if the water solubility of Ru2 can be improved enough for the studies above.