Abstract
Molecular packing controls optoelectronic properties in organic molecular nanomaterials. Here we report a donor–acceptor organic molecule (2,6-bis(4-cyanophenyl)-4-(9-phenyl-9H-carbazol-3-yl)pyridine-3,5-dicarbonitrile) that exhibits two aggregate states in aqueous dispersions: amorphous nanospheres and ordered nanofibres with π–π molecular stacking. The nanofibres promote sacrificial photocatalytic H2 production (31.85 mmol g−1 h−1) while the nanospheres produce hydrogen peroxide (H2O2) (3.20 mmol g−1 h−1 in the presence of O2). This is the first example of an organic photocatalyst that can be directed to produce these two different solar fuels simply by changing the molecular packing. These different packings affect energy band levels, the extent of excited state delocalization, the excited state dynamics, charge transfer to O2 and the light absorption profile. We use a combination of structural and photophysical measurements to understand how this influences photocatalytic selectivity. This illustrates the potential to achieve multiple photocatalytic functionalities with a single organic molecule by engineering nanomorphology and solid-state packing.
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Data availability
All data generated and analysed relevant to the study are included in the Article and its Supplementary Information files. The X-ray crystallographic coordinates for structures reported in this study have been deposited at the Cambridge Crystallographic Data Centre (CCDC), under deposition numbers 2157381 and 2157384 for CNP-C1 and CNP-C2, respectively. These data can be obtained free of charge from the CCDC via www.ccdc.cam.ac.uk/data_request/cif. Source data are provided with this paper.
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Acknowledgements
We thank the Engineering and Physical Sciences Research Council (EPSRC) for financial support under grants EP/N004884/1 and EP/P034497/1. TA measurements were performed at the University of Liverpool Early Career Researcher Laser Laboratory supported by UKRI-EPSRC grant EP/S017623/1 and the University of Liverpool, maintained and operated as a shared research facility by the Faculty of Science and Engineering. We are grateful to B. Greeves (University of Liverpool) for assistance with performing the spectroelectrochemical measurements and M. Volk for discussion on 1O2. H.Y. thanks the Leverhulme Trust via the Leverhulme Research Centre for Functional Materials Design for funding. H.Y. thanks M. Little for the input on the crystal measurements and discussion. C.L. thanks the China Scholarship Council for a PhD studentship. Weiwei Zhang acknowledges support from the Fundamental Research Funds for the Central Universities and Shanghai Pujiang Program (22PJ1402400). The TEM experiments in this paper were performed in the Albert Crewe Centre for Electron Microscopy at the University of Liverpool, maintained and operated as a shared research facility by the Faculty of Science and Engineering. Computing support from the High Performance Computing facility at the University of Liverpool is gratefully acknowledged.
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Contributions
H.Y. synthesized and characterized CNP nanoparticles, grew the crystals, and performed photocatalysis experiments and analysis. C.L. carried out TA, Raman experiments, spectroelectrochemistry, singlet oxygen measurements and spectra analysis with help from A.M.G. and A.J.C. T.L. performed DFT calculations. T.F. and L.C. measured the single crystal. S.Y.C. performed simulations on nanoparticle structures. L.L. helped with electrochemical characterization. Weiwei Zhang and Y.X. were involved in the analysis of CNP photoactivity. Wei Zhao helped with isotopic exchange experiments. M.B. and N.D.B carried out the HRTEM measurements. R.C. helped with the instrument build. X.L. synthesized the CNP molecules and performed the initial study. X.L., A.J.C. and A.I.C. supervised this work. All authors discussed the results and commented on the manuscript.
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Extended data
Extended Data Fig. 1 Single crystal structure of CNP.
a, Single crystal structure of the P212121 CNP phase grown by sublimation at 683 K under dynamic vacuum (grey, C; blue, N; write, H). b, The experimental X-ray diffraction pattern of CNP-C1. c, Single crystal structure of CNP-C2.
Extended Data Fig. 2 Transient absorption spectra of small molecule in THF.
a,b,c, Transient absorption spectra of donor (a), acceptor (b), and CNP molecule (c) (100 μM) in THF following 325 nm excitation with a power of 750 µW, respectively. d,e,f, Transient absorption spectra of donor (d), acceptor (e), and CNP molecule (f) (100 μM) in THF following 380 nm excitation with a power of 750 µW, respectively. All the samples are under an argon gas atmosphere in a 1 mm pathlength cuvette.
Extended Data Fig. 3 Cyclic voltammogram (CV) and spectroelectrochemical spectra of molecules in acetonitrile.
a, Cyclic voltammogram (CV) of CNP, donor, acceptor in acetonitrile recorded at 0.1 V s−1 from −2.6 V to +1.4 V vs Fc+/Fc. b-f, Spectroelectrochemical spectra in acetonitrile upon (1) stepwise increase of the potential from 0 to 1.2 V (CNP (b), acceptor (d)) and 0 to 1.4 V (donor (f)) and (2) stepwise decrease of the potential from 0 to -2.2 V (CNP (c), acceptor (e)) and 0 to -2 V (donor (g)), which are calibrated versus the ferrocene/ferrocenium redox couple.
Extended Data Fig. 4 Isotope labelling experiments.
a, Time course of the gas production of CNP-f (2.5 mg) in a D2O solution containing 0.1 M ascorbic acid (20 mL). The reactions were carried out under visible illumination (300 W Xe light source, λ > 420 nm) with side-illumination through a quartz window. Percentage of gas products were measured by mass spectrometry. b, Isotopic 18O2 labelling experiments with 18O2 in photocatalytic H2O2 production irradiated by 300 W Xe lamp fitted with a λ > 420 nm filter using 50 mg of the CNP-s in 18O2 environment. The signal of 16O2 was from air during GC-MS injection.
Extended Data Fig. 5 Isotope labelling experiments.
Transient absorption spectra and normalized single wavelength dynamics at the charge transfer states around 840–860 nm in the presence of 100 mM AA (CNP-s (a), CNP-f (c)) and the mixture of 100 mM AA and 3 wt% Pt (CNP-s (b), CNP-f (d)) in water on the fs–ns timescale.
Supplementary information
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Yang, H., Li, C., Liu, T. et al. Packing-induced selectivity switching in molecular nanoparticle photocatalysts for hydrogen and hydrogen peroxide production. Nat. Nanotechnol. 18, 307–315 (2023). https://doi.org/10.1038/s41565-022-01289-9
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DOI: https://doi.org/10.1038/s41565-022-01289-9