PHOTOCHEMISTRY OF INTERCALATED QUATERNARY DIAZAAROMATIC SALTS

Certain quaternary diazaaromatic salts intercalate between base pairs in calf thymus DNA and in synthetic polynucleotides. The intense fluorescence of these salts, as observed in dilute aqueous solution, is quenched upon intercalation due to electron abstraction from an adjacent base. This reaction is not sequence-specific. The resultant radical cation of the quaternary salt decays within 100 ps. Individual nucleotide monophosphates also transfer an electron to the excited singlet state of the salts, both in fluid solution and after complexation in the ground state. Illumination of a salt/nucleotide ground-state complex generates the corresponding radical ion pair, which decays within 100 ns. These results indicate that photoinduced electron-transfer processes involving intercalated dye molecules occur on faster (i.e., 2500-fold) time scales than for the corresponding complexed reactants and are highly reversible.