Electronic Effect of Substituents on the DNA Intercalation of Ruthenium(II)Polypyridyl Complexes

Abstract Five ruthenium(II) complexes, i.e. , [Ru(bpy) 2 (TIP)] 2+ (bpy=2,2′‐bipyridine; TIP=2‐thiophenimidazo[4,5‐ f ] [1,10]phenanthroline; 1 ), [Ru(bpy) 2 (5‐NTIP)] 2+ (5‐NTIP=2‐(5‐nitrothiophen)imidazo[4,5‐ f ] [1,10]phenanthroline; 2 ), [Ru(bpy) 2 (5‐MOTIP)] 2+ (5‐MOTIP=2‐(5‐methoxythiophen)imidazo[4,5‐ f ] [1,10]phenanthroline; 3 ), [Ru(bpy) 2 (5‐BTIP)] 2+ (5‐BTIP=2‐(5‐bromothiophen)imidazo[4,5‐ f ] [1,10]phenanthroline; 4 ), and [Ru(bpy) 2 (4‐BTIP)] 2+ (4‐BTIP=2‐(4‐bromothiophen)imidazo[4,5‐ f ] [1,10]phenanthroline; 5 ), were synthesized and characterized by elemental analysis and UV/VIS, IR, and 1 H‐NMR spectroscopic methods. The photophysical and DNA‐binding properties were investigated by means of UV and fluorescence spectroscopic methods and viscosity measurements, respectively. The results suggest that all five complexes can bind to CT‐DNA with various binding strength. Complexes 2 and 3 showed the strongest and the weakest binding affinity, respectively, among these five complexes. Due to the substituent position of the Br‐atom in the ligand, complex 5 interacted stronger with CT‐DNA than complex 4 . The binding affinities of the complexes decreased in the order 2, 5, 4, 1 , and 3 .