Laser Flash Spectroscopy of Methylene Blue With Nucleic Acids

Absorption spectra, fluorescence spectra and quantum yields, triplet state absorption spectra, yields and rates of decay have been obtained for methylene blue (MB+), MB+/CT‐DNA complexes and complexes of MB+ with the synthetic polynucleotides poly[d(G‐C)] and poly[d(A‐T)]. Strong fluorescence quenching is observed in the complexes of the dye with CT‐DNA and poly[d(G‐C)] concomitant with a decrease in the triplet yield. The fluorescence and triplet yield of MB+ with poly[d(A‐T)] are similar to those of the free dye. The triplet decay times are increased in all three polymer/dye complexes and show a decreased sensitivity to oxygen quenching. These results are interpreted in terms of the binding of the dye to these polymers and the implications of polymer binding on the photosensitizing properties of the dye are discussed.