  The photosynthetic apparatus of plants and bacteria combine atomically
precise pigment-protein complexes with dynamic membrane architectures to
control energy transfer on the 10-100 nm length scales. Recently, synthetic
materials have integrated photosynthetic antennae proteins to enhance exciton
transport, though the influence of artificial packing on the excited-state
dynamics in these biohybrid materials remains unclear. Here, we use the
adaptive Hierarchy of Pure States (adHOPS) to perform a formally exact
simulation of excitation energy transfer within artificial aggregates of light
harvesting complex 2 (LH2) with a range of packing densities. We find that LH2
aggregates support a remarkable exciton diffusion length ranging from 100 nm at
a biological packing density to 300 nm at the densest packing previously
suggested in an artificial aggregate. The unprecedented scale of these
calculations also underscores the efficiency with which adHOPS simulates
excited-state processes in realistic molecular materials.
