[Ru(bpy)(3-n)(dpb)(n)](2+): unusual photophysical property and efficient DNA photocleavage activity.

The sequential replacement of a bpy ligand (bpy = 2,2'-bipyridine) by a dpb ligand (dpb = 2,3-bis(2-pyridyl) benzoquinoxaline) in the series [Ru(bpy)(3-n)(dpb)(n)](2+) (n = 1-3) leads to a remarkable increase of the excited state lifetime, the (1)O(2) quantum yield, and the binding affinity toward dsDNA, rendering both [Ru(bpy)(dpb)(2)](2+) and [Ru(dpb)(3)](2+) efficient DNA photocleavage activities upon red light irradiation (>or=600 nm).