DNA photocleavage by a supramolecular Ru(II)-viologen complex

A novel Ru(II) complex possessing two sequentially linked viologen units, Ru-V-1-V-2(6+), was synthesized and characterized. Upon excitation of the Ru(II) unit (lambda(exc) = 532 nm, fwhm similar to 10 ns), a long-lived charge-separated (CS) state is observed (tau = 1.7 mus) by transient absorption spectroscopy. Unlike Ru(bPY)(3)(2+), which cleaves DNA upon photolysis through the formation of reactive oxygen species, such as O-1(2) and O-2(-), the photocleavage of plasmid DNA by Ru-V-1-V-2(6+) is observed both in air and under N-2 atmosphere (lambda(irr) > 395 nm).