[Ru(phen)2(dppz)]2+ as an efficient optical probe for staining nuclear components.

The 'molecular light switch' complexes [Ru(bpy)(2)(dppz)](2+) (1) and [Ru(phen)(2)(dppz)](2+) (2), where bpy=2,2'-bipyridine, phen=1,10-phenanthroline and dppz=dipyrido[3,2-a:2',3'-c]phenazine, have been explored as probes for diagnosing and staining nuclear components. The phen complex acts as a better staining agent for nonviable cells than for viable cells and exhibits a staining efficiency in tail region of comet more specific and stronger than the already known dye Hoechst 33258.