Basic Research Needs for Solar Energy Utilization - Office of ...

USING A BIO-INSPIRED SMART MATRIX TO OPTIMIZE ENERGY
LANDSCAPES FOR SOLAR FUELS PRODUCTION
In photosynthesis, complex protein structures control and optimize energy flow in a dynamic
fashion, leading to efficient solar energy conversion and storage. No artificial systems currently
implement this approach in a useful fashion, and assembly of such systems is currently beyond
the state-of-the-art for chemists. Development and use of smart matrices would revolutionize our
ability to control and implement solar-fuel-forming systems at the molecular level.
EXECUTIVE SUMMARY
A central challenge for solar fuels production is the development of efficient new photocatalysts
for solar energy capture, conversion, and storage. Biology has achieved the ideal of solarinitiated
water-splitting coupled to chemical energy storage using abundant, renewable, selfassembling
“soft” materials. The catalytic power and specificity that are key attributes of
enzyme-mediated catalysis have their origins in the active environment provided by the protein.
The proteins involved in the photosynthetic light-harvesting complexes and the reaction centers
are not mere inert scaffolds. They provide much more than just a means of optimally positioning
the chromophores and the electron-transfer cofactors. The medium provided by the protein
actively promotes, enhances, and indeed controls the light-harvesting and electron-transfer
reactions. This is a key feature of the natural system that allows it to operate efficiently. Current
bio-inspired solar-energy conversion systems have been able to replicate in a limited fashion the
light harvesting, directed energy transfer, and charge separation seen in photosynthesis.
However, so far, this has been achieved by using strong covalent bonds to link the molecular
components in the required configurations. Due to major limitations imposed by covalent
synthesis of large assemblies, construction of the next generation of bio-inspired solar-energy
conversion systems will require self-assembly of the molecular components into a “smart
matrix” that controls their key electronic properties. Understanding how the smart matrix
exercises dynamic control over the energy landscape of the active components within it is critical
to optimizing solar energy conversion efficiency. This control extends from the attosecond-long
electronic dynamics associated with nascent photon absorption and charge separation to the
minutes-and-longer control of atomic motions during the catalytic production of solar fuels.
Achieving efficient solar-energy conversion systems using smart matrices will require
(1) engineering proteins, polymers, membranes, gels, and other ordered materials to provide
tailored active environments (i.e., smart matrices); (2) incorporating bio-inspired cofactors
within the designed matrix; (3) integrating multiple cofactor-matrix assemblies to perform the
overall function; (4) characterizing the coupling between the cofactors and the matrix in natural
and bio-inspired systems using advanced techniques; (5) integrating experimental measurements
of structural and electronic dynamics with multi-scale theoretical approaches to achieve
fundamental breakthroughs in system design paradigms for solar energy capture and conversion
by supramolecular structures; and (6) mapping out and predicting optimized electronic and
structural energy landscapes for efficient formation of solar fuels.
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