Ground and excited-state interactions of coumarin and nucleotide base

Steady-state and time-resolved fluorescence measurements for a series of bichromophoric compounds containing 7-methoxy-coumarin and nucleotide base residues have been performed in water and in organic solvents. The data from these studies have been used to calculate the relative proportion of folded and extended conformations of bichromophores. Ground-state stacking interactions of coumarin and nucleotide base have been found to be limited to aqueous solution. The contribution of the dynamic quenching mechanism to the total fluorescence quenching in water has been estimated. The absence of dynamic quenching in organic solvents is.explained on the basis of the very short lifetime of the fluorophore in methanol.