Control of Electron-Transfer and DNA Binding Properties by the Tolyl Spacer Group in Viologen Linked Acridines

Novel water soluble viologen and pyridinium linked tolylacridines 1a,b and 2a,b were synthesized and their photophysical and DNA binding properties including the photoinduced electron-transfer reactions were investigated. When compared to the cases of the model tolylacridines 3a,b and the pyridinium linked derivatives 2a,b, the singlet excited states of 1a and 1b were efficiently quenched in water and methanol. Intramolecular quenching rate constants (kET) calculated in water are found to be 1.2 × 1010 and 8.8 × 1010 s-1 for 1a and 1b and 1.4 × 108 and 0.9 × 108 s-1 for 2a and 2b, respectively, suggesting thereby that the viologen moiety quenches the fluorescence of the acridine chromophore efficiently when compared to the case of the pyridinium moiety. From the intermolecular electron-transfer studies, it was observed that the singlet and triplet excited states of the acridine chromophore are capable of donating an electron to the viologen moiety. DNA binding studies indicated that the p-tolylacridine de...