Model systems for photosynthesis I. Energy transfer and light harvesting mechanisms

Absorption spectra, triplet state and fluorescence properties of solutions of chlorophylls b and a and pheophytins b and a in lecithin have been studied over a range of concentration from 10-4 to 5 x 10-2 mol l-1. Energy transfer has been investigated for the pairs chlorophyll b to a, pheophytins b to a, and is adequately described by the Förster inductive resonance mechanism . We have also examined the self-quenching of fluorescence and trip let state formation for each of the four molecules. With the exception of pheophytin b, which forms aggregates at high concentrations, there were no observable quenchers and, in each case, the half quenching concentration is close to that at which energy transfer between like molecules occurs. Mechanisms for this self-quenching and the possible relevance of these models to photo ­system II in photosynthesis are discussed.