We present a size-invariant (i.e., N0) scaling algorithm for simulating fluorescence spectroscopy in large molecular aggregates. We combine
the dyadic adaptive hierarchy of pure states (DadHOPS) equation-of-motion with an operator decomposition scheme and an efficient Monte
Carlo sampling algorithm to enable a formally exact, local description of the fluorescence spectrum in large molecular aggregates. Furthermore,
we demonstrate that the ensemble average inverse participation ratio of DadHOPS wave functions reproduces the delocalization extent
extracted from fluorescence spectroscopy of J-aggregates with strong vibronic transitions. This work provides a computationally efficient
framework for fluorescence simulations, offering a new tool for understanding the optical properties of mesoscale molecular systems.