Self-Assembled Nanoscale
DNA–Porphyrin Complex
for Artificial Light Harvesting
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Abstract
Mimicking green plants’ and bacteria’s
extraordinary
ability to absorb a vast number of photons and harness their energy
is a longstanding goal in artificial photosynthesis. Resonance energy
transfer among donor dyes has been shown to play a crucial role on
the overall transfer of energy in the natural systems. Here, we present
artificial, self-assembled, light-harvesting complexes consisting
of DNA scaffolds, intercalated YO-PRO-1 (YO) donor dyes and a porphyrin
acceptor anchored to a lipid bilayer, conceptually mimicking the natural
light-harvesting systems. A model system consisting of 39-mer duplex
DNA in a linear wire configuration with the porphyrin attached in
the middle of the wire is primarily investigated. Utilizing intercalated
donor fluorophores to sensitize the excitation of the porphyrin acceptor,
we obtain an effective absorption coefficient 12 times larger than
for direct excitation of the porphyrin. On the basis of steady-state
and time-resolved emission measurements and Markov chain simulations,
we show that YO-to-YO resonance energy transfer substantially contributes
to the overall flow of energy to the porphyrin. This increase is explained
through energy migration along the wire allowing the excited state
energy to transfer to positions closer to the porphyrin. The versatility
of DNA as a structural material is demonstrated through the construction
of a more complex, hexagonal, light-harvesting scaffold yielding further
increase in the effective absorption coefficient. Our results show
that, by using DNA as a scaffold, we are able to arrange chromophores
on a nanometer scale and in this way facilitate the assembly of efficient
light-harvesting systems