pH and DNA luminescence switching, DNA photocleavage and cytotoxic properties of two thiophene-containing ruthenium(II) complexes.

Two new Ru(II) complexes, [Ru(Htip)3]Cl2 (1) and [Ru(Htip)2(dppz)]Cl2 (2), were synthesised and were characterised. The ground- and excited-state acid-base properties of 1 and 2 were studied and demonstrated that 1 acted as a pH-induced "on-off-on" luminescence switch. The binding behaviours of 1 and 2 to calf thymus DNA were studied with absorption and emission spectroscopy, DNA viscosities and density functional theory calculations. 2 was found to act as a DNA molecular light switch and as an efficient photocleaver of pUC 18 DNA. The cytotoxicities of the complexes were evaluated with the MTT method and it was found that 1 displayed apparent anticancer activity against MCF-7 cell, whereas 2 exhibited more potent and wider-spectrum antitumor activities against all cancer cell lines tested.