Theories for kinetics and yields of fluorescence and photochemistry: how, if at all, can different models of antenna organization be distinguished experimentally?

The models most commonly used to describe the antenna organization of the photosynthetic membrane are the connected units model and the domain model. The theoretical descriptions of the exciton dynamics according to these models are reviewed with emphasis on a common nomenclature. Based on this nomenclature we compare for the two models the kinetics and yields of photochemistry and fluorescence under non-annihilation and annihilation conditions both under continuous light and under flash excitation. The general case is considered, that all initially open reaction centers become gradually closed and that exciton transfer between photosynthetic units (PSUs) is possible. Then, calculated kinetics and yields depend on the model assumptions made to account for the exciton transfer between PSUs. Here we extend the connected units model to flash excitation including exciton-exciton annihilation, and present a new simple mathematical formalism of the domain model under continuous light and flash excitation without annihilation. Product and fluorescence yields predicted by the connected units model for different degrees of connectivity are compared with those predicted by the domain model using the same sets of rate constants. From these calculations we conclude that it is hardly possible to distinguish experimentally between different models by any current method. If at all, classical fluorescence induction measurements are more suited for assessing the excitonic connectivity between PSUs than ps experiments. (C) 1999 Elsevier Science B.V. All rights reserved.