Synthesis and spectroscopic DNA binding studies of homoleptic and heteroleptic ruthenium(II) complexes with imidazo[4,5-f] [1,10]phenanthroline or its derivatives

Two series of new complexes, Ru(phen)2L]2+ and RuL3]2+, where phen = 1,10-phenanthroline, and L denotes imidazo4,5-f]1,10]phenanthroline (IP) or 2-(4-R-phenyl)imidazo4,5-f]1,10]phenanthroline(PIP, R = H; HOP, R = –OH; MOP, R = –OMe; DMNP, R = NMe2; CLP, R = Cl; NOP, R = NO2), were synthesized and characterized. Their binding to calf thymus DNA was investigated using electronic absorption and emission spectroscopy. Ru(IP)3]2+ and each Ru(phen)2 L]2+ showed dramatic absorption hypochromism and bathochromicity, as well as steady-state emission intensity and excited-state lifetime enhancements {except nonluminescent Ru(phen)2NOP]2+} associated with the presence of DNA, inferring that they bind to DNA by intercalation. These phenomena were not observed for RuL3]2+ type complexes (except L = IP), indicating that they bind to DNA at most through electrostatic interactions.