  A nanoring-rotaxane supramolecular assembly, with a Cy7 cyanine dye
(hexamethylindotricarbocyanine) threaded along the axis of the nanoring, has
been synthesized as a model for the energy transfer between the light
harvesting complex LH1 and the reaction center in purple bacteria
photosynthesis. The complex displays efficient energy transfer from the central
cyanine dye to the surrounding zinc porphyrin nanoring. We present a
theoretical model that reproduces the absorption spectrum of the nanoring and
quantifies the excitonic coupling between the nanoring and the central dye,
explaining the efficient energy transfer and elucidating the similarity with
structurally related natural light harvesting systems.
