Fluorescence-detected two-dimensional electronic spectroscopy: A coarse-grained simulation approach

Fluorescence-detected two-dimensional electronic spectroscopy (F-2DES) offers superior sensitivity compared to the traditional coherent two-dimensional electronic spectroscopy (2DES) technique. However, theoretical modeling remains essential to interpret F-2DES spectra, especially for multi-chromophoric systems. While widely used to study excitation energy transfer in molecular assemblies, even conventional 2DES faces computational challenges for large systems. To address these challenges, we extend a recently developed coarse-grained method for 2DES to simulate F-2DES and account for signatures of exciton-exciton annihilation events that affect cross-peak intensities in F-2DES. We then apply this approach to the light-harvesting II complex of purple bacteria, a well-studied benchmark system, and we find that F-2DES simulations reproduce experimental cross-peaks at zero and early waiting times. Moreover, disabling exciton-exciton annihilation recovers results identical to standard 2DES simulations, confirming that the observed cross-peaks arise from annihilation events, as hypothesized earlier. The implemented method opens the door for future exploration of waiting-time dynamics and extends the possibility of predicting F-2DES spectra to extensive photosynthetic systems.