Ferrocene derivatives containing 4-amino-1,8-naphthalimide linked on the 4-position of the naphthalimide ring have been synthesized. The electrochemical data and the free energy of charge separation (ΔGcs) showed that photo-induced electron transfer (PET) from the ferrocenyl unit to the naphthalimide moiety is thermodynamically feasible for these ferrocence derivatives. Their absorption spectra show that the electronic interaction between the ferrocenyl unit and the naphthalimide moiety are very different for these ferrocene derivatives. We attribute these differences due to different spacers used to link the ferrocenyl unit and the naphthalimide moiety. Measurements of the fluorescence spectrum and the fluorescence lifetime confirmed that the fluorescence of the naphthalimide is strongly quenched by the effective PET from the ferrocenyl units to the naphthalimide moieties. The PET path in 6-[4-(2-oxo-2-ferrocenyl-ethyl)-piperazin-1-yl] -benzo[de]isoquinoline-1,3-diones can be switched off by both the oxidation of the ferrocene unit and the protonation of the alkylated amine group. These kind of dyads can be employed as dual-mode chemical (protons)/electrochromic molecular switches. © 2002 Published by Elsevier Science B.V.