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

Abstract

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.