Measurement of in situ structure and structural dynamics in biomimetic supramolecular solar fuel catalysts

Photosynthesis serves as a paradigm for the design of molecular systems for solar energy conversion based on modular architectures, hierarchically assembly, and host-guest chemistry linked by non-covalent chemistry. Recent examples include the development of photosystem I-catalyst hybrids and a variety of supramolecular analogues that couple photosensitizers to catalysts for solar hydrogen production. Each differs considerably in efficiency of solar hydrogen production. A central challenge lies in the development of methods for in-situ characterization of biomimetic supramolecular structure that can be correlated to catalysis. Here, we demonstrate opportunities to characterize the structures of these modular supramolecular assemblies using synchrotron X-ray scattering. We have used a combination of wide-angle x-ray scattering of the molecular components and the completed assemblies to resolve interference patterns characteristic of the ground-state assembly. Further, we have developed laser-pump/70 ps X-ray probe pulse techniques for direct detection of atomic reorganization accompanying photochemical charge separation in solution-state supramolecular systems.