The role of accessory bacteriochlorophylls in the primary charge transfer in the photosynthetic reaction centers

In this work we present a model to elucidate the unidirectionality of the p rimary charge separation process in the bacterial reaction centers (RCs) wh ere two symmetric ways of electron transfer (ET), starting from the common electron donor, are possible. We have used a model of three sites/molecules with ET beginning at site 1 with an option to proceed to site 2 or site 3. The dependence of the asymmetry in ET on the value of the sink parameter, introduced through an additional imaginary diagonal matrix element of the H amiltonian, was investigated. Results show indeed that the unidirectionalit y of the ET generated in the system of three molecules depends strongly on the value of the energy levels of the accessory bacteriochlorophyll molecul es. (C) 2001 Elsevier Science B.V. All rights reserved.