A Molecular Tetrad That Generates a High-Energy Charge-Separated State by Mimicking the Photosynthetic Z-Scheme
2016 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 138, no 11, 3752-3760 p.Article in journal (Refereed) PublishedText
The oxygenic photosynthesis of green plants, green algae, and cyanobacteria is the major provider of energy rich compounds in the biosphere. The so-called "Z-scheme" is at the heart of this "engine of life". Two photosystems (photo system I and II) work in series to build up a higher redox ability than each photosystem alone can provide, which is necessary to drive water oxidation into oxygen and NADP(+) reduction into NADPH with visible light. Here we show a mimic of the Z-scheme with a molecular tetrad. The "tetrad Bodipy-NDI-TAPD-Ru is composed of two different dyes-4,4-difluoro-1,3,5,7-tetramethyl-2,6-diethy1-4-bora-3a,4a-diaza-s-indacene (Bodipy) and a Ru-II(bipyridine), (Ru) derivative-which are connected to a naphthalene diimide (NDI) electron acceptor and tetraalkylphenyldiamine (TAPD) playing the role of electron donor. A strong laser pulse excitation of visible light where the two dye molecules (Ru and Bodipy) absorb with equal probability leads to the cooperative formation of a highly energetic charge-separated state composed of an oxidized Bodipy and a reduced Ru. The latter state cannot be reached by one single photon absorption. The energy of the final charge-separated state (oxidized Bodipy/reduced Ru) in the tetrad lies higher than that in the reference dyads (Bodipy-NDI and TAPD-Ru), leading to the energy efficiency of the tetrad being 47% of the sum of the photon threshold energies. Its lifetime was increased by several orders of magnitude compared to that in the reference dyads Bodipy-NDI and TAPD-Ru, as it passes from about 3 ns in each dyad to 850 ns in the tetrad. The overall quantum yield formation of this extended charge-separated state is estimated to be 24%. Our proof-of-concept result demonstrates the capability to translate a crucial photosynthetic energy conversion principle into man-made molecular systems for solar fuel formation, to obtain products of higher energy content than those produced by a single photon absorption.
Place, publisher, year, edition, pages
2016. Vol. 138, no 11, 3752-3760 p.
IdentifiersURN: urn:nbn:se:uu:diva-294307DOI: 10.1021/jacs.5b12650ISI: 000372854200023PubMedID: 26925987OAI: oai:DiVA.org:uu-294307DiVA: diva2:929571
FunderKnut and Alice Wallenberg FoundationSwedish Energy Agency