The copper complex [Cu((t)BuPhimp)(Cl)] (1) derived from tridentate ligand (t)BuPhimpH having N2O donors was synthesized, and its molecular structure was determined. A phenoxyl radical complex was generated in solution at room temperature using Ce(IV). The nuclease and anticancer activities of 1 were investigated. The roles of the tert-butyl group and singlet oxygen in the DNA cleavage activity were also discussed.