Fluorescence of zinc porphyrin in zinc porphyrin-C-60 dyads is enhanced by applying an electric field (1) due to a field-induced deceleration of the electron transfer rate from the singlet excited state of zinc porphyrin to C-60 in the Marcus top region. Free-base porphyrin-C-60 dyads exhibit the opposite electric field effect, since the electron transfer from the singlet excited state of free-base porphyrin to C-60 is in the Marcus normal region far from the top. (C) 2002 Elsevier Science B.V. All rights reserved.