In order to study the effect of size on the stoichiometry of complexes formed as intermediates in photoinduced electron transfer (PET) reaction we considered electron transfer between three alpha,omega-diphenylpolyenes; all-s-trans-1,4-diphenylbuta-1,3-diene (DPB), all-s-trans-1,6-diphenylhexa-1,3,5-triene (DPH) and all-s-trans-1,8-diphenylocta-1,3,5,7-tetraene (DPO) and N,N-dimethylaniline (DMA). Two types of complexes, exciplex and triplex, were identified with the help of an external magnetic field. These results were further supported by steady-state fluorescence study, where the spectra showed existence of both complexes depending on concentration of DMA and chain length of the polyenes. (C) 2004 Elsevier B.V. All rights reserved.