Excited state behaviour of substituted dipyridophenazine Cr(III) complexes in the presence of nucleic acids

The photophysics and photochemistry of [Cr(phen)(2)(dppz)](3+) and its 11,12-substituted derivatives [Cr(phen)(2)(X(2)dppz)](3+) {X = Me or F} have been studied in the presence of purine nucleotides or DNA using steady state and time-resolved absorption and luminescence spectroscopy. 5'-Adenosine monophosphate (5'-AMP) shows only a weak interaction with the excited states of each complex. By contrast they are efficiently quenched by 5'-guanosine monophosphate (5'-GMP), consistent with photo-induced electron transfer. Laser flash photolysis spectroscopy in the presence of 5'-GMP suggests that both forward and back electron-transfers are rapid. All complexes also display a strong affinity for DNA and evidence for both static and dynamic quenching mechanisms is provided.