Fluorescence quenching of Y-4,9-dihydro-4,6-dimethyl-9-oxo-1H-imidazo-1,2-a purine (Y_t base) and the model compounds Y_t(CH₂)_nadenine by α-bromonaphthalene

The fluorescence quenching of Y-4,9-dihydro-4,6-dimethyl-9-oxo-1H-imidazo-1,2-a purine (Y_t base) and of some model compounds Y_t(CH₂)_nadenine (n = 2, 3, 5) by α-bromonaphthalene was studied in various solvents. The dependence of the ratio k/k_d (where k is the rate constant for energy transfer from Y_t to α-bromonaphthalene and k_d is the diffusion rate constant) on the integrated overlap of the Y_t fluorescence and the singlet-triplet absorption of α-bromonaphthalene was linear. The constant k for the model compounds varied with the length of the polymethylene chain and attained its lowest value for n = 3. This is probably due to an increased degree of base stacking interaction in the trimethylene-bridged compound.