Sustainable aviation fuels from CO 2 by cyanobacteria and photochemistry utilizing visible light for triplet-induced dimerization of isoprene Martin Axelsson, Sindhujaa Vajravel, Haining Tian, and Henrik Ottosson Uppsala University, Sweden Current aviation biofuel production depends on biomass, which creates competition for farmland and contributes to deforestation. There is a pressing need for a carbon-neutral method that utilizes CO 2 directly for jet fuel production. Isoprene, a volatile hydrocarbon, can be generated from CO 2 through a direct, light-driven process using genetically modified photosynthetic cyanobacteria [1] . The isoprene can then undergo a photo-driven dimerization reaction, catalysed by a triplet sensitizer, to produce C10 hydrocarbons. Using a photochemical step instead of completely relying on the cyanobacteria for production of the C10 hydrocarbons, facilitates harvesting as the volatile isoprene evaporates through the cell walls to the headspace of the photobiological reactor in contrast to larger hydrocarbons that accumulate inside the cells potentially leading to toxification. The C10 hydrocarbons formed in the photochemical dimerization reaction can subsequently be converted into jet fuel through hydrogenation [2] . The efficiency of the dimerization reaction is notable with ketone sensitisers, but they only absorb near-UV and UV light [3] . To address this limitation, we have assessed PbCsBr 3 quantum dots (QDs) to use their tuneable light-absorbing properties as visible light triplet sensitisers for the dimerization process. The heavy atom makeup of the QDs gives excitons a mixed spin character due to the large spin-orbit coupling [4,5] . This means that any exciton generated can be harvested by isoprene in the form of a triplet, this extraction can be further enhanced by attaching an energy transmitter on the surface of the QDs. PbCsBr 3 quantum dots also have a high overlap between absorption and emission, meaning a slight loss of energy from harvesting to triplet transfer. All of these characteristics make QDs an outstanding candidate as the photocatalyst for isoprene dimerization. In this project, we have evaluated the efficiency of isoprene dimerization using QDs and a few other photocatalysts to move the reaction into the visible-light spectrum. References
1. Englund et. al. Metab. Eng. 2018 , 49, 164-177 2. Rana et. al. Green Chem. 2022 , 24, 9602-9619 3. Cid Gomes et. al. ACS Sustainable Chem. Eng. 2025 , 13, 2467-2476 4. Scholes, Adv. Funct. Mater. 2008 , 18, 1157-1172 5. Jiang, Weiss, J. Am. Chem. Soc. 2020 , 142, 15219-15229
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