J. Am. Chem. Soc. 133, 11985–11993 (2011)

Credit: © 2011 ACS

Using the energy of visible light to fuel chemical conversions in a similar manner to photosynthesis is extremely attractive. Multiple chromophore systems, attached to dendrimers or protein assemblies, have been constructed that are able to capture light and transport the excitation energy in one direction through donor–acceptor energy-transfer processes, but organizing a large number of multiple chromophores with precision remains challenging.

Yan Liu and co-workers from Arizona State University have now used a DNA scaffold to prepare rapid and efficient light-harvesting antennas. A seven-helix DNA bundle, in which six helices surround a protruding one, holds cyclic arrays of three chromophores attached to the DNA fairly rigidly — either through a base or directly incorporated into the backbone — at well-controlled inter-chromophore distances. They are arranged to favour a stepwise energy transfer from the primary donor to the intermediate donor, then to the acceptor at the protruding site.

The researchers prepared a series of antennas in which the relative ratios between the three chromophores are varied, and studied their energy-transfer processes and light-harvesting abilities. In all cases, the only energy transfer observed was a stepwise, unidirectional transfer cascade from the primary donor to the secondary, and then to the acceptor, demonstrating the efficacy of the DNA scaffold. The light-harvesting abilities of the antennas were most efficient when a large number of donor chromophores were present.