Behaviour in the Absence of DNA

The photophysics and photochemistry of Ru(II) complexes have been extensively studied and good reviews are av able on this subject [1,86,87]. The type of reactivity associated with Ru(II) polypyridyl complexes in the excited state depends on the nature of this excited state and consequently on the different possible photophysical pathways controlling the luminescence lifetimes. For most polypyridyl Ru(II) complexes (for example Ru(bpy), Rufphenls , Ru(bpz)3. .. Fig. 2) [1, 86, 87], population of the excited singlet MLCT state is followed by crossing to the triplet MLCT state ( MLCT) with a quantum yield 

Whether a photoredox or a photodechelation process takes place, depends on the presence of reducing or oxidising agents in the solution, and on the energy difference between the MLCT and MC. An estimation of this energy 

The trends in the properties described for this series of HAT complexes, are similar for the corresponding series based on the TAP ligand [92], although HAT complexes are more oxidising than TAP complexes. As will be illustrated further, the modulation of the oxidation power will be reflected in the photoreactivity of the Ru(II) complexes versus the various DNA bases. 

It is also noteworthy that complexes containing ligands such as TAP, HAT, bpz (2,2 -bipyrazine) or bipym (2,2 -bipyrimidine) (Fig. 2), have free non-chelated nitrogen atoms. It has been shown that all these compounds are all more basic in the excited state than the ground state [75,93,94], so that the excited states are already protonated at pH 5-6 on the non-chelated nitrogen atoms. 

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