Theory and Simulations of Fluorescence-Detected Two-Dimensional Electronic Spectroscopy: From Rigorous Quantum Mechanics to Simple Kinetic Models.

Action-detected two-dimensional electronic spectroscopy is a collection of emerging nonlinear spectroscopic techniques that offer notable advantages over coherently detected two-dimensional electronic spectroscopy. Fluorescence-detected 2D electronic spectroscopy has been used to study molecular aggregates with very high detection sensitivity and spatial resolution. However, the information content that is extracted from action-2D electronic spectroscopy is not fully understood. Simulations have proven indispensable in interpreting the spectral features of various processes such as exciton-exciton annihilation, exciton dynamics, and incoherent population mixing. Here we benchmarked commonly used approximate methods for simulating fluorescence-detected 2D electronic spectroscopy for a molecular dimer in a wide range of system parameters. We compared approximate spectra to the rigorously derived approach which only requires the knowledge of the molecular Hamiltonian and transition dipole moments. This work established the regimes of validity of approximate and practical methods for simulating action-detection 2D signals in relation to the time scales of competing processes in typical molecular aggregates.