On the interpretation of decay associated spectra in the presence of time dependent spectral shifts

Time dependent spectral shifts caused by energetic relaxation processes frequently contribute to time resolved spectral data. They make a global analysis of transient spectra challenging, since the basic assumption of separability of time and frequency dependence does not hold. We compare the global analysis results of synthetic transient spectra to a Taylor expansion of their spectral shape at infinite time. Thereby we can elucidate the correlation of time constants and decay associated spectra resulting from global analysis with the underlying shift dynamics. The obtained insights are applied to transient absorption spectra of Coumarin 152 and its solvation dynamics.