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 p hotosynthetic membrane are the connected units model and the domain model. The theoretical descriptions of the exciton dynamics according to these mod els are reviewed with emphasis on a common nomenclature. Based on this nome nclature we compare for the two models the kinetics and yields of photochem istry and fluorescence under non-annihilation and annihilation conditions b oth under continuous light and under flash excitation. The general case is considered, that all initially open reaction centers become gradually close d 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 conne cted 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 fl uorescence yields predicted by the connected units model for different degr ees of connectivity are compared with those predicted by the domain model u sing the same sets of rate constants. From these calculations we conclude t hat it is hardly possible to distinguish experimentally between different m odels by any current method. If at all, classical fluorescence induction me asurements are more suited for assessing the excitonic connectivity between PSUs than ps experiments. (C) 1999 Elsevier Science B.V. All rights reserv ed.