Downhill energy transfer via ordered multichromophores in light-harvesting capsules

A variety of light-harvesting capsules were successfully constructed by assembling polyelectrolyte complexes and antenna dyes of graduated absorption energy into nanoscale walls (thickness of a single layer around 2 nm). Two-step downhill energy transfer was demonstrated with absorption and fluorescence spectroscopy,for the first time on light-harvesting capsules. Energy transfer occurs parallel to the capsule surface if the dyes are coadsorbed to the preassembled capsule wall. Energy transfer perpendicular to the surface was achieved by sequentially assembling the dyes in different layers of the wall. Although perpendicular energy transfer is less efficient because of longer intermolecular distances, utilization of J-aggregates and optimization of dyed combinations and dye ratios yielded an efficient energy cascade along three components. The light-harvesting capsules are analogous to. the light reactions of photosynthesis in chloroplasts.