In light-harvesting antennae, the decay of r(t) indicates the elementary timescales of exciton migration, be it through incoherent hopping or exciton relaxation (Kennis et al. 1997b; Nagarajan et al. 1996; Novoderezhkin
et al. 1998; Savikhin et al. 1994, 1998, 1999; Vulto et al. 1999; Vulto et al. 1997). Energy transfer or exciton relaxation processes often occur among (pools of) Chls that have their absorption maxima at similar wavelengths. Consequently, these processes are associated with small Selleckchem Y27632 spectral shifts of the ΔA GSK3235025 spectra and are therefore difficult to observe under magic angle detection conditions. Through time-resolved anisotropy experiments, the timescales of such fast
exciton migration events can accurately be determined. mTOR inhibitor Data analysis In time-resolved spectroscopic experiments, the very large amounts of data collected can be analyzed by global and target analysis techniques (Van Stokkum et al. 2004). A typical time-resolved experiment ΔA(λ,τ) in fact consists of a collection of thousands of data points, i.e., tens to hundreds wavelengths times one to two hundred data points. In order to extract valuable information, one could simply take slices of the data; for instance, one could take one wavelength and look at its evolution in time (a so-called kinetic trace), or one could plot the signal at different wavelengths for a given time point (a ΔA spectrum). This is normally Carbohydrate the first stage of the data analysis where the experimentalist has a glimpse of an expected (or unexpected) process. The next step in the data analysis is to apply the so-called global analysis techniques, in an attempt to distill the overwhelming amount of data into a relatively small number of components and spectra. In the most basic model, the femtosecond transient
absorption data are globally analyzed using a kinetic model consisting of sequentially interconverting evolution-associated difference spectra (EADS), i.e., 1→2→3→··· in which the arrows indicate successive monoexponential decays of increasing time constants, which can be regarded as the lifetime of each EADS. The first EADS correspond to the time-zero difference spectrum. This procedure enables a clear visualization of the evolution of the (excited) states of the system. Based on the insight obtained from this model and from the raw data, one can then take a further step in the analysis and apply a so-called target kinetic scheme. The EADS that follow from the sequential analysis are generally made up from a mixture of various molecular species. In general, the EADS may well reflect mixtures of molecular states.