| Abstract: | Abstract— –The method of Weber and Teale for determining absolute fluorescence quantum yield of dyes in solution was modified for determination of the yield of bacteriochlorophyll fluorescence from chromatophores and whole cells of photosynthetic bacteria. Measured yields ranged from about 1–6 per cent. The yield depended on intensity and wavelength of the exciting light. The higher yield at higher light intensity was interpreted as due to saturation of photosynthesis. The lower yield in some strains when excited at 810 nm was attributed to preferential excitation of the reaction center pigment P800. From this study and the lifetime measurements of others, the relation τ=Q.τ0 was substantiated for the fluorescence of bacteriochlorophyll in vivo, τ being the actual lifetime, τ0 the intrinsic lifetime as estimated from the absorption band area, and Q the quantum yield of fluorescence. |
