Universiteit Leiden

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Reedijk Symposium 2019: Function-based nonadiabatic principles for artificial photosynthesis with high yield

Friday 25 October 2019
Gorlaeus Building
Einsteinweg 55
2333 CC Leiden


With Magic-angle spinning NMR, cryo-Electron microscopy, and accurate computer simulations we resolve universal mechanisms of biological photosynthesis across taxonomies and species, and study how to transfer biological design principles to chiral biomimetic nanomaterials for high yield artificial photosynthesis. Photosynthetic complexes are activated in the ground state by local mismatches that selectively enhance conformational dynamics to perform the biological functions of light harvesting, charge separation and catalysis upon excitation by light. This leads us into a function based framework of limited complexity for the design of semisynthetic and biomimetic artificial photosynthesis components.

In this year's LIC symposium I will present the current status and provide underpinning with examples from past and ongoing research in our group. In photosynthetic reaction centers, the local stress induced by the protein matrix leads to partial charge transfer between the His and its chlorophyll partner that oscillates back and forth between overlapping macrocycles upon twisting of the His to establish dynamic heterogeneity in a homogeneous chiral structural framework. The twisting promotes energy transfer and mixing of charge transfer character into the excited state coupled to protonation change of the matrix by a quasi quantum coherent process denoted Non-adiabatic Conversion by Adiabatic Passage (NCAP). In this mechanism, an adiabatic sweep induces nonadiabatic matrix elements between a reactant and a product state with resonant coupling to a vibration that is self-selected from the vibrational background. This process is best described in a doubly rotating interaction frame to reveal the coherent conversion of a reactant into a product with near unity yield. To make the step to artificial photosynthesis we study for many years chlorosome bacteriochlorophyll antenna aggregates. This is a rather unique biological system without protein. Starting from an idealized symmetric model for the structure determined by cryo-EM and MAS NMR, we have added static and dynamic heterogeneity to track how ultrafast energy transfer can be stimulated by NCAP.

Very recently, we have prepared chiral semisynthetic peptide-porphyrin antenna constructs, and the data indicate that a chiral packing may be sufficient to activate NCAP processes. For water oxidation catalysis we also project the biological system on a function based framework to reduce the complexity. Here we study the level crossings between reactant and product intermediate states and the possibility to induce nonadiabatic transitions while conserving electronic spin angular momentum. A first experimental example of vibrationally assisted rapid catalysis was found in copper oxide nanoleaves with induced asymmetry. All in all, our portfolio of experimental and theoretical results leads us to conclude that with the function based framework of the biological paradigms, we can build on principles of coherent rotations in spin space in a magnetic field to establish quantum principles of high yield NCAP by crossing of reactant and product states for a novel class of asymmetric responsive matrix materials that perform semiclassical chemical conversions by twisting, as in chiral biological systems.

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