Photoinduced Electron Transfer in Langmuir-blodgett Films

Photoinduced electron transfer from an excited donor molecule (oxacyanine) to an acceptor molecule (viologen) located at the same interface in monolayer assemblies has been studied by measuring steady state fluorescence quenching and the excited state decay of the donor molecule. Donor and acceptor molecules are incorporated in matrix monolayers of arachidic acid and methyl arachidate, with a molar ratio 9:1. It is seen that the electron transfer efficiency increases with increasing donor density (a~ = 0.005-0.425 rim-2). The fluorescence decay functions of the donor are described by assuming at least two fluorescent species and the results show that the contribution of long-lived species increases with increasing donor density. The average rate constant for the excited state electron transfer depends on the donor density and was found to be 2 x 10 s st (as = 0.025 nm2; ad = 0.005 nm2). The results are rationalized in terms of energy delocalization via incoherent exciton hopping.