Two-dimensional optical spectroscopy of homo- and heterodimers

Abstract

We theoretically study the two-dimensional (2D) spectroscopy of molecular dimers. The spectra are first analyzed within an electronic level model. It is demonstrated how the angular average over molecular orientations influences the features of the spectra. Methods to calculate angular averaged vibronic spectra within perturbation theory are compared. We systematically document changes in the 2D-spectra upon going from homo- to heterodimers. In particular, it is demonstrated that large-amplitude off-diagonal peaks appear for heterodimers even in the limit of vanishing coupling. This is related to the difference in the excitation energies of the two different monomers. For homodimers with equal monomer excitation energies, such peaks become diagonal peaks and thus cannot be isolated.