Time-resolved femtosecond transient absorption (fs-TA) spectroscopy is a powerful method to investigate the photoinduced processes in molecular systems, that is, their relaxation and reaction pathways upon photoexcitation on time scales between a few femtoseconds and hundreds of nanoseconds. Analysis of the resulting set of spectra generally requires advanced techniques which try to fit a kinetic model to the data, for example via global lifetime analysis or multivariate curve resolution. While these methods are widely used, they require a priori information on the sampled system, as they require a kinetic model, i.e., the number of processes contributing to the data. Choosing the right number of processes is often not an easy task and heavily influences the results.1
2D correlation spectroscopy (2DCOS), a method popular especially in the field of vibrational spectroscopy, offers a way to analyze systematic changes in datasets recorded under a changing external variable, by recovering the cross-correlation function of the spectral variables.2 2DCOS is ideally suited to TA spectroscopy, as the external variable (time) is inherent to the method. Furthermore, it does not require a specific kinetic model or other a priori information. TA-2DCOS allows the extraction of the number of kinetic processes contributing to the data set alongside qualitative spectral signatures. We demonstrate that TA-2DCOS can reproduce the results obtained by common, model dependent, methods for well understood systems. 2DCOS can therefore serve as an alternative analysis method for fs-TA spectra and offer an ideal starting point for quantitative methods, if a priori information is not available.3
Acknowledgement: This work was supported by the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) in the framework of SFB/TRR 234 CataLight (subprojects C2 and A1, project number 364549901) and project BO 4700/4-1.