Global analysis transient absorption

Any advanced absorbance/fluorescence spectrophotometer designed for routine acquistion of absorption or emission on the subsecond time scale. The basic goal is to obtain a series of complete UV/visible or fluorescence spectra as a function of time, usually after samples are mixed in a stopped-flow device. Such data help the investigator to infer the most likely structures of transient intermediates whose electronic spectra or fluorescence spectra can be determined by deconvoluting the spectra with appropriate reaction kinetic simulation software or by some other global analysis method (Fig. 1). 

Transient absorption spectroscopy has been a conventional technique for studying the configurational (conformational) changes that are reflected in the Tn <— T, optical transition. Picosecond to microsecond time-resolved, pump and probe measurement has been widely used to examine the triplet-state isomerizations as far as each ris-T, and the all-trans-Tj species are selectively observed. Even when their wavelengths are very similar to one another, the SVD and global-fitting analysis can successfully identify a set of triplet species appearing in different time-scales, when a correct kinetic model is built. 

Transient absorption traces are most often fitted with a sum of exponentials, and the decay rates are related to the processes taking place. When a range of wavelengths is probed, all the decay curves can be fitted simultaneously to a minimum number of decay parameters in a global analysis according to... 

In this chapter we focus on the application of trilinear models in fluorescence spectroscopy, because that is where we have most experience. However, these trilinear models are also applicable to other kinds of excited-state spectroscopy, such as transient absorption spectroscopy. Along the way, we also discuss bilinear and other models, including global analysis. ... 

Electronic absorption spectroscopy is also a useful technique for the characterization of Cr intermediates. When coupled with global kinetic analysis, ligand stoichiometries, and spectra of transient species in the redox chemistry of Cr can be determined. The first applications of this global analysis to biologically relevant systems involved studies of the Cr(Vl) reactions with the main biological reductants Cys, GSH, and ascorbate (70, 97). The distinct electronic absorption features of the Cr(VI), Cr(V), Cr(lV), and Cr(lll) oxidation states... 

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