We have synthesized and characterized a new G G mismatch binding ligand containing a TEMPO radical. The two mismatch binding ligands cooperatively bound to the CGG/CGG triad and an apparent binding constant was in the order of 10(5)M(-1). The tumbling of the ligand on a DNA duplex was ten times slower than that of the unbound ligand. Asymmetric addressability of two TEMPO radicals on DNA is shown.