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

Figure 40 X-ray diffraction determined snapshots with 100-ps time-resolution of atomic
motions coupled to CO photolysis in myoglobin, achieved using pump-probe X-ray
crystallographic techniques (Source: Schotte et al. 2004)
Recent work has demonstrated the critical need for structural techniques to resolve the local site
electronic or nuclear motions responsible for gated electron transfer in reaction centers that
cannot be detected with crystallographic techniques as typically applied to photosynthetic
proteins (see Figure 41). The increasing complexities of supramolecular solar-energy-converting
assemblies, and the sensitivity of light-initiated chemistry to the details of structure and
dynamics in molecular and host environments, suggest that similar limitations may ultimately be
reached with bio-inspired supramolecular structures. The promise of breakthroughs can be
envisioned by combining information from diffraction
approaches with advances in the application of multidimensional
magnetic, vibrational, and optical
Qb
spectroscopies for mapping dynamic electron and nuclear
coupling during the time-course of photochemical
reactions. These approaches, combined with in-situ nearfield
and atomic probe techniques, offer promise to achieve
breakthroughs in the visualization of mechanisms for sitespecific,
microscopic control of solar-energy conversion.
Electronic Dynamics. Opportunities to directly image the
electronic dynamics most intimately linked to solar-energy
capture and conversion processes are demonstrated by
advances in coherent and energy-loss X-ray and optical
spectroscopies. Recently, an elegant demonstration of the
ability for multi-dimensional, coherent electronic
absorption spectroscopies to resolve dynamic electron
131
Figure 41 Light-induced Fourier
difference maps adjacent to the Qb
site in B. viridis reaction centers
(Source: Baxter et al. 2004)