Deriving intrinsic parameters of photoinduced electron transfer reaction from the transient effect probed by picosecond time-resolved fluorescence quenching

Fluorescence quenching of a pyrylium salt (PDP2+) by toluene in acetonitrile gives rise to a nonexponential decay. This behavior is ascribed to the so-called transient effect occurring at high quencher concentrations for diffusion-controlled reactions. First, the Kalman filter was used to deconvolute the original signal from the experimental decay curve and the response function of the apparatus. This treatment led to a calculated deconvoluted decay curve which enabled the transient effect analysis to be conducted. This real decay curve was then analyzed using two models, The Smoluchowski-Collins-Kimball (SCK) model, applied to diffusion-controlled reactions, yielded the reaction radius r(AD) and the intrinsic rate constant k(act) of the bimolecular electron transfer reaction. The Marcus electron transfer/diffusion (ETD) model, which provides a powerful method to evaluate the electronic coupling H-el associate with the reaction, was also used but is more difficult to handle due to extensive computational needs. Finally, the adequacy of the two models (SCK and ETD) for analysis of the transient effect was addressed, as well as the appropriateness of the Kalman filter for fluorescence signal deconvolution.