Functionalized DNA Nanostructures for Light Harvesting and Charge Separation

Mimicking natural photosynthesis by covalently arranging antenna and charge separation units is a formidable task. Many such beautiful supramolecular complexes have been designed and synthesized with large efforts, some of which are presented in this special issue. The ability to predict relative position of and electronic coupling between the active components in covalent arrays is quite high but there are two obvious drawbacks with the covalent approach. Firstly, as the size grows the complexity of the organic synthesis increases and secondly, sensitivity to light-induced damage becomes a major issue if covalent bonds are broken. Self-assembly of the photoactive components should, in principle, provide a solution to both these issues but generally the ability to predict position and electronic coupling is too low to have the designed properties needed for a functional artificial photosynthetic complex. Here, we present an approach of using DNA as a template for arranging both charge separation units and antenna molecules that govern long-range energy transfer. Of particular interest is the ability of DNA to function as a scaffold for chromophores, either through covalent attachment, or through non-covalent association by means of intercalation or grove binding. Using controlled positioning of dyes, multichromophoric assemblies can be created, capable of long range communication through multi-step energy transfer. This facilitates creation of DNA-based photonic devices for both light harvesting and directed information transfer. The channeled excitation energy can be transformed site specifically to chemical energy by charge separation of DNA linked porphyrins. A two phase system is discussed, in which the DNA is located in buffered solution whereas the hydrophobic porphyrins, responsible for the charge separation reaction, are located in the lipid bilayer of liposomes or supported lipid bilayers