Basic Research Needs for Solar Energy Utilization - Office of ...
Basic Research Needs for Solar Energy Utilization - Office of ...
Basic Research Needs for Solar Energy Utilization - Office of ...
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coupling in multi-c<strong>of</strong>actor-containing assemblies has used 2-D transient optical spectroscopy to<br />
map the time evolution <strong>of</strong> coupled electrons in light-harvesting proteins (see Figure 42). The<br />
crystal structures <strong>of</strong> these light-harvesting proteins show impressively large arrays <strong>of</strong> c<strong>of</strong>actors.<br />
The complexities <strong>of</strong> these arrays and their protein hosts prevent a definitive determination <strong>of</strong><br />
structure-based function and elucidation <strong>of</strong> underlying design principles. Two-dimensional<br />
transient optical and related coherent spectroscopies <strong>of</strong>fer new approaches <strong>for</strong> achieving<br />
breakthroughs in understanding the design and function <strong>of</strong> multi-c<strong>of</strong>actor arrays. These<br />
spectroscopies are well-suited <strong>for</strong> extension to in-situ analysis <strong>of</strong> c<strong>of</strong>actor arrays within<br />
specialized micro-environments.<br />
Building upon these coherent optical techniques are emerging analogous X-ray spectroscopic<br />
techniques <strong>for</strong> deciphering electronic structure at metal centers and finer, higher-resolution<br />
length scales. Pioneering examples include inelastic X-ray scattering techniques that have<br />
imaged spatial and temporal electric-field-induced electron density disturbances associated with<br />
charge and electric-field perturbations in water with 40-attosecond (10 -18 s) time resolution<br />
(Abbamonte et al. 2004). These measurements allowed mapping <strong>of</strong> electronic disturbances<br />
calculated to be produced by an oscillating molecular dipole and diffusing ion fields. These<br />
studies suggest unprecedented opportunities to map the dynamic electronic responses <strong>of</strong> solarfuel-producing<br />
materials.<br />
Multi-scale Theoretical/Computational Approaches. The complex nature <strong>of</strong> supramolecular<br />
assemblies associated with a variety <strong>of</strong> host architectures and the anticipated explosion in<br />
experimental detail concerning light-initiated electronic and nuclear dynamics raise significant<br />
theoretical challenges. New, multi-scale theoretical/computational methods are critically needed<br />
to account <strong>for</strong> the complexities <strong>of</strong> excited-state energetics applied across multiple spatial length<br />
scales relevant to supramolecular structures within complex host architectures, and on the range<br />
<strong>of</strong> time scales encompassing solar-energy capture, conversion, and storage. New theoretical<br />
methods are essential <strong>for</strong> establishing predictive methods to accelerate the design <strong>of</strong> efficient<br />
systems <strong>for</strong> solar fuels production.<br />
Figure 42 Dynamically resolved electronic coupling in the FMO protein using 2-D pulsed<br />
spectroscopy (Source: Brixner et al. 2005)<br />
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