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Reversible fluorenol photobases that perform CO2 capture and concentration from ambient air

Nature Chemistry (2025)Cite this article

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Abstract

Leading strategies for the capture of CO2 from point sources and directly from the atmosphere face high energy costs for thermal sorbent regeneration. Photochemical processes, driven by sunlight as the sole external stimulus, offer a promising alternative. Despite many reported examples of light-induced pH swings using metastable photoacids, the complementary mode of operation, using photoswitchable bases, has not been extensively considered. This is due in part to the rarity of photobases that can support large, reversible pH jumps in water. Here we report the design of fluorenol-based Arrhenius photobases that take advantage of excited-state aromaticity and ground-state antiaromaticity to generate large basicity swings with high reversibility. The system is oxygen stable, can be driven by natural sunlight and captures/concentrates CO2 from ambient air. We elucidated the mechanism of C–O dissociation using transient absorption spectroscopy to understand the high efficiency of hydroxide release. This study provides a framework for the design of photoreversible aqueous bases and guiding principles for their use in solar-powered CO2 management.

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Fig. 1: Design and characterization of fluorenol photobases.
Fig. 2: Light-driven reversible CO2 capture.
Fig. 3: Ultrafast spectroscopic characterization of PBMeOH in MeCN/H2O.
Fig. 4: Energy-level diagram of PBMeOH photochemical homolysis and heterolysis pathways.
Fig. 5: Potential mechanisms of CO2 release.
Fig. 6: Thermodynamic diagram for reversible CO2 capture.

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All data supporting the findings of this study are available within the article and its Supplementary Information. Source data are provided with this paper.

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Acknowledgements

R.Y.L. is grateful to the Corning Fund for Faculty Development and the Salata Institute for Climate and Sustainability for partial support of this project. This work was supported by the National Science Foundation through a CAREER award to R.Y.L. (CHE-2338206), a graduate research fellowship for A.Y.W. and support to D.G.N. from the Office of Naval Research (N00014-25-1-2100).

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Authors and Affiliations

  1. Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA

    Michael Purdy, Ariel Y. Wang, Matthew C. Drummer, Daniel G. Nocera & Richard Y. Liu

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  1. Michael Purdy
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Contributions

M.P. designed, synthesized and structurally characterized all photobases. M.P. and A.Y.W. optically characterized the photobases using UV–vis spectroscopy. M.P. performed all CO2 experiments. A.Y.W. performed all density functional theory calculations. M.C.D. designed and performed all TA measurements. M.P., M.C.D., D.G.N. and R.Y.L. wrote the paper. All authors interpreted the results and commented on the paper.

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Correspondence to Richard Y. Liu.

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Extended data

Extended Data Fig. 1 Ultrafast spectroscopic characterization of PBMeOH in dry MeCN.

All transient absorption (TA) presented in this figure were performed on air-equilibrated solutions of PBMeOH in a 1-cm pathlength quartz cuvette with the pump laser set to 360 nm. (a) Femtosecond TA spectra of PBMeOH in dry MeCN. (b) Kinetic traces at 750 nm (red dots) with monoexponential fits (red line). (c) Nanosecond TA spectra of PBMeOH in dry MeCN. (d) Kinetic traces of the nsTA data at 414 nm (grey dots) with monoexponential fit (red line).

Source data

Supplementary information

Supplementary Information

Supplementary Figs. 1–28, Discussion and Table 1.

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Source Data Fig. 2

Source data for Fig. 2.

Source Data Fig. 3

Source data for Fig. 3.

Source Data Fig. 5

Source data for Fig. 5.

Source Data Extended Data Fig. 1

Source data for Extended Data Fig. 1.

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Purdy, M., Wang, A.Y., Drummer, M.C. et al. Reversible fluorenol photobases that perform CO2 capture and concentration from ambient air. Nat. Chem. (2025). https://doi.org/10.1038/s41557-025-01901-0

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