Deconvolution of femtosecond time-resolved spectroscopy data in multivariate curve resolution. Application to the characterization of ultrafast photo-induced intramolecular proton transfer

In femtosecond absorption spectroscopy, deconvolution of the measured kinetic traces is still an important issue as photochemical processes that may possess shorter characteristic times than the time resolution of the experiment are usually considered. In this work, we propose to perform deconvolution of the time-dependent concentration profiles extracted from multivariate curve resolution (MCR) applied to spectrokinetic data. The profiles are fitted with a model function including a description of the instrumental response function (IRF) of the experiment. The method combines the potential benefits of soft-modeling data analysis with the ones of hard-modeling for parameter estimation. The potential of the method is demonstrated first analyzing five synthetic data sets for which IRF of different widths are simulated. It is then successfully applied to resolve femtosecond UV-visible transient absorption spectroscopy data investigating the photodynamics of salicylidene aniline, a photochromic molecule of wide interest. Considering a time resolution of 150 fs for the IRF, a characteristic time of 45 fs is recovered for the first step of the photo-induced process which consists of an ultrafast intramolecular proton transfer. Our results also confirm the existence of an intermediate species with a characteristic time of 240 fs.