Multiresponse parameter estimation and compartmental analysis of time resolved fluorescence spectra. Application to conformational dynamics of charge-separated species in solution

Abstract

2 Lecture conformational changes of intramol. charge-transfer species were studied by means of time resolved fluorescence spectroscopy. From a time resolved fluorescence spectrum the parameters which describe a kinetic, compartmental, model as well as the model dependent fluorescence spectral-shape parameters were estd. Two methods for parameter estn. were compared nonlinear least squares and multiresponse. Anal. of residuals revealed shortcomings of the exptl. setup, in particular time jitter. The concn. fluctuations induced by this time jitter could cause failure of the usual nonlinear least squares model fit, whereas the multiresponse parameter estn. was successful. Different compartmental models with the same kinetic parameters result in identical residuals. Thus a distinction can only be made on the basis of the accompanying estd. spectra. Due to the restriction that fluorescence spectra are nonneg., the anal. of a two-component system was only satisfactory using a model in which a slower decaying component was a reaction product of a faster decaying component. A three-component system was satisfactorily described by a model with three independently decaying components