Prompt and Delayed Fluorescence of Some Dna Adsorbates

The absorption and prompt fluorescence spectra of twelve cationic compounds in the free and bound states were surveyed, and four compounds selected for detailed study, viz: proflavine, benzoflavine, acridine orange and thioflavine T. The absorption spectra, prompt fluorescence spectra and delayed fluorescence and phosphorescence spectra of these four compounds in fluid solutions in the free and bound states were measured. The shifts in the promp fluorescence bands of the diaminoacridines on adsorption were found to differ significantly from those of the other compounds, and the behaviour of acridine orange was found to be different from that of the other two diaminoacridines. All three diaminoacridines gave E‐type delayed fluorescence in the free and bound states. The ordered structure of the strongly binding adsorption sites in native DNA is associated with a higher intensity of delayed fluorescence than is observed from the diaminoacridines in the free state or adsorbed on denatured DNA. Quenching experiments with proflavine indicated that, in the weakly binding sites, its triplet is easily quenched by unadsorbed quenchers, but in the strongly binding sites its triplet is quenched only with great difficulty.