Light Induced Electron Transfer between Spatially Separated Donor and Acceptor

Abstract Quenching of fluorescence due to electron transfer is observed in monolayer assemblies when electron donor and electron acceptor, both immobile, are either in the same monolayer or in adjacent monolayers. When the donor and acceptor monolayers are separated by two fatty acid interlayers no fluorescence quenching is detected. Two types of light induced electron transfer have been observed. The donor is excited and the electron is transferred from the S1 state of the donor into the lowest unoccupied orbital of the acceptor. The donor fluorescence is quenched. The acceptor is excited and the electron is transferred from the S0 state of the donor into the highest occupied orbital of the acceptor. The acceptor fluorescence is quenched. In both processes the initial situation is recovered by back transfer of an electron from the reduced acceptor to the highest occupied orbital of the donor. These electron transfer processes have been studied by varying the concentration of the acceptor. The fluorescence quenching depends on the average distance R̃ between acceptor molecules and values of R̃1/2 (average distance in the acceptor layer at which the fluorescence intensity is half of the intensity without electron transfer) have been determined. The value of R̃1/2 depends on the energetic position of both the electron donating level and the electron accepting level as calculated from electrochemical and spectroscopic data.