Abstract
Optically activated reactions initiate biological processes such as photosynthesis or vision, but can also control polymerization, catalysis or energy conversion. Methods relying on the manipulation of light at macroscopic and mesoscopic scales are used to control on-surface photochemistry, but do not offer atomic-scale control. Here we take advantage of the confinement of the electromagnetic field at the apex of a scanning tunnelling microscope tip to drive the phototautomerization of a free-base phthalocyanine with submolecular precision. We can control the reaction rate and the relative tautomer population through a change in the laser excitation wavelength or through the tip position. Atomically resolved tip-enhanced photoluminescence spectroscopy and hyperspectral mapping unravel an excited-state mediated process, which is quantitatively supported by a comprehensive theoretical model combining ab initio calculations with a parametric open-quantum-system approach. Our experimental strategy may allow insights in other photochemical reactions and proof useful to control complex on-surface reactions.
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Data availability
Source data are available via Zenodo at https://doi.org/10.5281/zenodo.10547040. Additional datasets are available from the corresponding authors upon reasonable request.
Code availability
The code used to calculate the results shown in this work is available from the corresponding authors upon reasonable request.
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Acknowledgements
We would like to thank V. Speisser and H. Sumar for technical support; G. Rogez for help with ultraviolet–visible spectroscopy; and A. Boeglin, L. E. P. López, S. Jiang, Ó. J. Arrate and A. Borissov for discussions. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 771850) (G.S., F.S. and A.R.), the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 894434 (A.R.) and the SNSF under the Postdoc.Mobility grant agreement no. 206912 (K.K.). This work is supported by ‘Investissements d’Avenir’ LabEx PALM (ANR-10-LABX-0039-PALM) (T.N.). T.N. acknowledges the Lumina Quaeruntur fellowship of the Czech Academy of Sciences. Computational resources were supplied by the project ‘e-Infrastruktura CZ’ (e-INFRA CZ LM2018140) supported by the Ministry of Education, Youth and Sports of the Czech Republic. We acknowledge financial support from the Agence Nationale de la Recherche under grant ATOEMS ANR-20-CE24-0010 (S.B.).
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A.R. and G.S. conceived the project. A.R., K.K., M.R., F.S., S.B. and G.S performed the experiments and analysed the data. E.D. etched the STM tips using a focused ion beam. T.N. performed the theoretical calculations and analysed the results. All authors discussed the results and contributed to revisions of the paper.
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Extended data
Extended Data Fig. 1 STM characterization and the scheme of the experimental set-up.
a, STM overview image of the H2Pc/NaCl/Ag(111) sample, ML - monolayers. Size: 36.5 × 36.5 nm2, V = -2.5 V, I = 5 pA. b, Optical set-up used in the experiment. SPF - shortpass filter, LPF - longpass filter, BS - beamsplitter.
Extended Data Fig. 2 Tautomerization analysis.
a, Current time trace with tautomerization events marked by ’ × ’. b, Numerical derivative of a. c, Histogram of current values in a, the solid line represents a fit, which is a sum of two Gaussians. d, Difference image obtained by subtracting the images representing configuration A and configuration B. Parameters: V = 0.55 V, I = 10 pA, P ≈ 15 μW, hνin = 2.00 eV, scale bar: 1 nm.
Extended Data Fig. 3 Characterization of TEPL and tautomerization.
a-c, TEPL intensity (orange rectangles) and tautomerization frequency (grey circles) of H2Pc recorded as a function of the laser power for three different excitation energies. All measurements are recorded at the extremity of a pyrrole unit. Integration range of the TEPL spectra: 1.79-1-82 eV, V = 0.55 V, current set-point I = 2 pA, the light intensity is corrected for the detection efficiency. The solid lines are linear fits to the data. d, PLE spectra recorded for two different laser beam alignments that are optimized for 1.82 eV and 1.84 eV excitation energy, respectively. The feature that corresponds to the Qx resonance (1.81 eV) is clearly visible on top of the broad distribution that is centred around the optimal excitation wavelength. The traces are vertically offset for clarity. P < 1μW, I = 10 pA, V = 0.55 V. e, TEPL spectra recorded on a decoupled H2Pc molecule (black line) on NaCl/Ag(111) (V = 0.55 V) and on clean (grey line) NaCl/Ag(111) (V = - 1 V). hνin = 1.953 eV, P ≈ 15μW, I = 2 pA, t = 90 s. The longpass filter (LPF) edge is indicated. f, Background-corrected TEPL spectrum.
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Rosławska, A., Kaiser, K., Romeo, M. et al. Submolecular-scale control of phototautomerization. Nat. Nanotechnol. (2024). https://doi.org/10.1038/s41565-024-01622-4
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DOI: https://doi.org/10.1038/s41565-024-01622-4
