Influence of excitonic coupling, static disorder, and coherent dynamics in action-2D electronic spectroscopy of a molecular dimer model

We investigate the spectral features of Action-2D Electronic Spectroscopy (A-2DES) using a molecular dimer model across different regimes of excitonic coupling. By explicitly including a second-excited state for each chromophore, we simulate A-2DES spectra ranging from the non-interacting limit to the strong-coupling case, focusing on the significance of cross peaks. While for weak excitonic coupling, cross peaks can be understood as the incoherent mixing of linear signals of the two chromophores, these features reflect excitonic delocalization as the coupling increases. We highlight that A-2DES offers enhanced sensitivity to coherent excited-state dynamics, particularly in the intermediate-coupling regime, where it provides higher contrast compared to its coherent-detected counterpart. Finally, we show the different influences of static disorder on the line shapes of diagonal and cross peaks. Notably, since cross peaks exhibit rephasing capability for increasing excitonic coupling, the contribution of incoherent mixing becomes less significant in inhomogeneous samples. These findings support the potential of A-2DES for investigating excitonic dynamics in small multi-chromophoric systems.