The fluorescence of pyrene can be quenched by spiropyran (SP) due to the intermolecular photoinduced electron transfer (PET). However, the fluorescence of the ensemble solution of pyrene (PY) and SP restores nearly to the initial value of the pure solution of PY after the consecutive actions of Fe(ClO4)(3) and UV light. This is owing to the fact that the open form of spiropyan can be coordinated to ferric ion, and as a result the reversible photo-control of the intermolecular PET reaction from SP to the excited PY can be realized under light irradiation in the presence of ferric ion. (C) 2004 Elsevier B.V. All rights reserved.