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(X2dppz)]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.