Supramolecular Architectures for Artificial Photosynthesis

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• Professor Marcella Bonchio (University of Padova and ITM-CNR, Department of Chemical Sciences)
• Wednesday 23 January 2019, 15:45-16:45
• Wolfson Lecture Theatre, Department of Chemistry.

If you have a question about this talk, please contact Lingtao Kong.

All of Earth’s oxygen is the result of water oxidation performed by photosynthetic organisms using solar light as the only energy source. The O2 necessary for our aerobic life is produced by the photocatalytic cleavage of the extremely stable H-O-H bonds. Making oxygen is exceptionally difficult and lethal for any biological factory, which calls out a continuous self-repair cycle during oxygenic photosynthesis. Indeed, and despite the vast bio-diversity footprint, just one specialized protein complex is used by Nature as the H2O -photolyzer: photosystem II (PSII). Man-made systems are still far from replicating the complexity of PSII . High resolution imaging of the PSII “core” complex shows the ideal co-localization of multi-chromophore Light Harvesting antennas with the functional Reaction Center (LH-RC). Our results overcome the classical “photo-dyad” model, based on a donor-acceptor binary combination. Here we report the self-assembly of multi-perylenebisimide chromophores (PBI) shaped to function by interaction with a polyoxometalate water oxidation catalyst (Ru4POM). The resulting [PBI]5Ru4POM complex is identified as the minimal photosynthetic unit, formed both in solution and on photoelectrodes, showing a: (i) a red-shifted, light harvesting efficiency (LHE>40%), (ii) favorable exciton accumulation and negligible excimeric loss; (iii) a robust amphiphilic structure; (iv) dynamic aggregation into large 2D-paracrystalline domains. Our results include the X-ray diffraction analysis of a dense, quasi-hexagonal packing of the functional motif, showing a striking analogy with the coexistence of fluid-to-crystalline phases in the native photosynthetic membrane. Photoexcitation of the PBI -antenna triggers one of the highest driving force for photo-induced electron transfer applied so far. The modularity of the building blocks, the simplicity of the non-covalent chemistry and the biomimetic appeal of the supramolecular approach, offer a unique opportunity for innovation in Artificial Photosynthesis.

1) Scheuring, S. & Sturgis, J. N. Chromatic Adaptation of Photosynthetic Membranes. Science 309, 484–487 (2005). 2) Sartorel, A., Carraro, M., Toma, F. M., Prato, M. & Bonchio, M. Shaping the beating heart of artificial photosynthesis: oxygenic metal oxide nano-clusters. Energy Environ. Sci. 5, 5592 (2012). 3) Sartorel, A. et al. Water Oxidation at a Tetraruthenate Core Stabilized by Polyoxometalate Ligands: Experimental and Computational Evidence To Trace the Competent Intermediates. J. Am. Chem. Soc. 131, 16051–16053 (2009). 4) Piccinin, S.; Sartorel, A.; Aquilanti, G.; Goldoni, A.; Bonchio, M.; Fabris, S. Water oxidation surface mechanisms replicated by a totally inorganic tetraruthenium-oxo molecular complex. Proc. Natl. Acad. Sci. 110, 4917–4922 (2013) 5) Toma, F. M. Prato, M. & Bonchio, M. et al. Efficient water oxidation at carbon nanotube–polyoxometalate electrocatalytic interfaces. Nat. Chem. 2, 826–831 (2010).

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