Theory of excitation energy transfer (EET) between donor and acceptor molec
ules in the intermediate coupling case is constructed. This theory interpol
ates theories of exciton and Forster mechanism. We also derived formulas of
criterion among exciton, intermediate coupling and Forster mechanisms. The
theory was applied to the light-harvesting system LH2 of photosynthetic ba
cteria. (C) 2000 Elsevier Science B.V. All rights reserved.