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Manganese(i) complexes with metal-to-ligand charge transfer luminescence and photoreactivity

Abstract

Precious metal complexes with the d6 valence electron configuration often exhibit luminescent metal-to-ligand charge transfer (MLCT) excited states, which form the basis for many applications in lighting, sensing, solar cells and synthetic photochemistry. Iron(ii) has received much attention as a possible Earth-abundant alternative, but to date no iron(ii) complex has been reported to show MLCT emission upon continuous-wave excitation. Manganese(i) has the same electron configuration as that of iron(ii), but until now has typically been overlooked in the search for cheap MLCT luminophores. Here we report that isocyanide chelate ligands give access to air-stable manganese(i) complexes that exhibit MLCT luminescence in solution at room temperature. These compounds were successfully used as photosensitizers for energy- and electron-transfer reactions and were shown to promote the photoisomerization of trans-stilbene. The observable electron transfer photoreactivity occurred from the emissive MLCT state, whereas the triplet energy transfer photoreactivity originated from a ligand-centred 3ππ* state.

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Fig. 1: Molecular structures of the ligands and complexes (isolated as PF6 salts) explored in this work.
Fig. 2: Steady-state absorption and emission spectroscopy.
Fig. 3: Time-resolved and (spectro-)electrochemical data for [Mn(Ltri)2]+.
Fig. 4: Dual emission at 77 K, different excited states and their photo-reactivities.
Fig. 5: Photoinduced energy and electron transfer.

Data availability

All pertinent experimental procedures, materials, methods and characterization data (NMR spectroscopy, electrospray ionization mass spectrometry, X-ray diffraction, as well as optical spectroscopic and electrochemical data) are provided in this article and its Supplementary Information. Crystallographic data for [ZnCl2(Lbi)·0.5C2H4Cl2] have been deposited at the Cambridge Crystallographic Data Centre under deposition number CCDC 2047767. Copies of data can be obtained free of charge from www.ccdc.cam.ac.uk/structures/. Source data are provided with this paper.

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Acknowledgements

O.S.W. thanks the Swiss National Science Foundation (grant nos 200021_178760 and 206021_157687) for financial support. C.K. acknowledges a Novartis University of Basel Excellence Scholarship for Life Sciences.

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Contributions

P.H. carried out the synthetic, spectroscopic and electrochemical work and analysed data, C.K. provided guidance in the spectroscopic work, designed the photochemical studies and helped in data analysis, C.B.L. provided guidance in the synthetic, spectroscopic and electrochemical work, D.H. performed the NMR studies and O.S.W. conceived the project and provided guidance. All the authors contributed to the writing and editing of the manuscript and gave approval to its final version.

Corresponding author

Correspondence to Oliver S. Wenger.

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The authors declare no competing interests.

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Supplementary information

Supplementary Information

NMR spectroscopy, electrospray ionization mass spectrometry, X-ray diffraction, as well as optical spectroscopic and electrochemical data; Supplementary Schemes 1 and 2, Figs. 1–56 and references 1–23.

Supplementary Data

Crystallographic data for [ZnCl2(Lbi)·0.5C2H4Cl2], CCDC 2047767.

Source data

Source Data Fig. 2

UV-vis absorption and luminescence spectra.

Source Data Fig. 3

UV-vis transient absorption, time-resolved emission, cyclic voltammetry and spectro-electrochemistry data.

Source Data Fig. 4

UV-vis absorption, luminescence and excitation spectra.

Source Data Fig. 5

UV-vis transient absorption and time-resolved luminescence data.

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Herr, P., Kerzig, C., Larsen, C.B. et al. Manganese(i) complexes with metal-to-ligand charge transfer luminescence and photoreactivity. Nat. Chem. 13, 956–962 (2021). https://doi.org/10.1038/s41557-021-00744-9

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