Real Space Analysis of Excitonic Interactions and Coherence Length in Helical Aggregates†

The effective exciton coherence length in molecular aggregates is calculated using a nonlocal, real-space representation of the linear optical response. Simulations of polarized absorption and linear dichroism demonstrate that the spectra depend on local properties of the molecular aggregate segment where the exciton coherence is delocalized. This allows us to limit the calculations to small segments of a large aggregate, avoiding the complexity of computing long-range coherences