Application of decay- and evolution-associated spectra for molecular systems with spectral shifts or inherent inhomogeneities

Decay- and evolution-associated spectra (DAS and EAS) are among the most popular methods for global analysis of time-resolved spectroscopy data. To interpret the obtained results in terms of a physical model, the system under consideration must satisfy several assumptions-spectral and temporal independence and lack of intrinsic disorder. In this work we study possible applicability of the DAS/EAS analysis for the time-resolved fluorescence spectra of several model systems, which fail to satisfy the required assumptions. We show that time-dependent spectral shifts can be distinguished by systematic comparison of DAS/EAS with different number of compartments. Somewhat unexpectedly, we demonstrate that DAS/EAS are rather robust for small systems even when they possess inherent disorder of excitation energy transfer or relaxation rates. In the case of larger molecular aggregates, the interpretation of DAS/EAS becomes much more ambiguous as the obtained results cannot be easily related to a physical kinetic and/or structural model.