Effect of solvent on the absorption spectra and Stokes’ shift of absorption and fluorescence of chlorophylls

Abstract

The absorption and fluorescence spectra of chlorophyll-a and chlorophyll-b solutions in a concentration of 6 · 10−6 M were determined in 22 solvents. The positions and the molar extinction coefficients of the red absorption band, the positions of the fluorescence bands, the oscillator strengths of the red bands and the Stokes’ shifts are tabulated. The results can be summarized as follows: The changes in the oscillator strength and the Stokes’ shifts obey roughly the theory of “internal field effect”. An evaluation of this effect yields 0.34 and 0.50 for the ratios of the polarizability of the chlorophylls and the Onsager radius of the solvents, for chlorophyll-a and chlorophyll-b, respectively. The results indicate that chlorophyll-b is more sensitive to environmental effects than chlorophyll-a.