MOLECULAR SWITCHES OF FLUORESCENCE OPERATING THROUGH METAL CENTERED REDOX COUPLES

Three-component molecular systems (redox active subunit)-spacer-(light -emitting fragment) can operate as fluorescence switches, following th e alternate addition of an oxidizing agent and a reducing agent (or th e adjustment of the potential of the working electrode in an electroly sis experiment). The redox active subunit typically consists of a meta l centred redox couple (M(n + 1+)/M-n (+)), encircled by a macrocyclic receptor, and switching efficiency requires that one of the two oxida tion states quenches the proximate fluorophore and the other does not. Four ON/OFF systems, based on either the Cu-II/Cu-I or Ni-III/Ni-II c ouple, will be discussed. The nature of the quenching process responsi ble for the OFF state, either electron transfer or energy transfer, is related to the length and to the flexibility-rigidity of the spacer. (C) 1998 Elsevier Science S.A.