Determination of the photoinduced electron transfer rate constant in Langmuir-Blodgett films by time-resolved fluorescence

The feasibility of a relevant analysis of the fluorescence decays of Langmu ir-Blodgett-Kuhn films where electron and energy transfer occur simultaneou sly is demonstrated. Starting from a stretched exponential, describing Fors ter-type energy transfer, a model describing simultaneous photoinduced elec tron transfer and energy transfer is developed. In this model a binomial di stribution of electron donors (pyrene) is assumed in the layer adjacent to the excited probe (Rhodamine G). When the fluorescence decays of two or thr ee samples with different concentrations of electron donors are analyzed si multaneously with the decay of a sample containing no electron donor, relia ble values of the global parameters (the fluorescence decay time of the unq uenched probe, the rate constant for electron transfer, and the rate consta nt for energy transfer to a trap) could be obtained. The local parameters ( the average number of electron donors in a site opposite the probe and the fraction of the monolayer containing an electron donor) are, however, highl y correlated. For the concentration range investigated, the decay parameter s do not depend on the emission wavelength.