Self-Quenching and Sensitization of Fluorescence of Chlorophyll Solutions

The intensity of fluorescence of solutions of chlorophyll (either a or b) is sensibly independent of concentration, for values less than 2×10−3m. At higher concentrations, the fluorescence decreases with increasing concentration, conforming to the empirical equation, If,max/If=1+4300m2. The absorption spectrum of chlorophyll a is the same at 0.02m as it is for very dilute solutions. These results, as well as the observed temperature coefficient of the fluorescent intensity, indicate that the self-quenching of chlorophyll solutions is not due to the formation of non-fluorescent dimers nor to collisions of the second kind, but is very probably related to the resonance exchange of excitation (16, 17) between an excited and normal chlorophyll molecule. Measurements of the fluorescence intensity of solutions containing mixtures of chlorophylls a and b indicate that chlorophyll b can sensitize the fluorescence of chlorophyll a, and that the fluorescence of chlorophyll b is more strongly quenched by a than it is by itself.