Abstract— Site‐selection fluorescence spectra of chlorophyll b in membranes of lecithin vesicles and in the solvents ethanol, n‐butanol, n‐butyl acetate, 2‐methyl tetrahydrofuran and toluene are presented. The spectra in vesicles display zero‐phonon lines as pronounced as those in the best organic glasses. The characteristics of the distributions of O—O transition energies and of the electron‐phonon couplings allow to infer the position of the chlorophyll molecule in the membrane of vesicles. It is thus found that the chromophore of chlorophyll b is situated in the layer formed by the ester moieties of the lecithins, i. e. close to the surface of the membrane but not in direct contact with the aqueous phase.