Probing Charge-Transfer Processes in a Covalently Linked [Ge9]-Cluster Imine Dyad

C60 donor dyads in which the carbon cage is covalently linked to an electron-donating unit have been discussed as one possibility for an electron-transfer system, and it has been shown that spherical [Ge9] cluster anions show a close relation to fullerenes with respect to their electronic structure. However, the optical properties of these clusters and of functionalized cluster derivatives are almost unknown. We now report on the synthesis of the intensely red [Ge9] cluster linked to an extended π-electron system. [Ge9{Si(TMS)3}2{CH3C=N}-DAB(II)Dipp]− (1−) is formed upon the reaction of [Ge9{Si(TMS)3}2]2− with bromo-diazaborole DAB(II)Dipp-Br in CH3CN (TMS=trimethylsilyl; DAB(II)=1,3,2-diazaborole with an unsaturated backbone; Dipp=2,6-di-iso-propylphenyl). Reversible protonation of the imine entity in 1− yields the deep green, zwitterionic cluster [Ge9{Si(TMS)3}2{CH3C=N(H)}-DAB(II)Dipp] (1-H) and vice versa. Optical spectroscopy combined with time-dependent density functional theory suggests a charge-transfer excitation between the cluster and the antibonding π* orbital of the imine moiety as the cause of the intense coloration. An absorption maximum of 1-H in the red region of the electromagnetic spectrum and the corresponding lowest-energy excited state at λ=669 nm make the compound an interesting starting point for further investigations targeting the design of photo-active cluster compounds.

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Funding Information: The authors thank the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation, project number 245845833) within the International Research Training Group IRTG 2022 (ATUMS) for financial support and the Bavarian State Ministry of Science and the Arts for funding this work in the scope of the project “Solar Technologies go Hybrid”. E.T. and J.H. acknowledge funding by the DFG‐TRR 325‐444632635. A.K. and J.H. acknowledge funding from the DFG through the excellence cluster ‐conversion, under Germany's Excellence Strategy—EXC 2089/1—390776260. CW thanks the Studienstiftung des Deutschen Volkes for granting a PhD scholarship. A.J.K. thanks the Academy of Finland for funding (grant 340584) and CSC, the Finnish IT Center for Science for computational resources. The authors thank Dr. Max Schütz and M. Sc. Maximilian Muhr (Chair of Inorganic and Metal‐Organic Chemistry, Prof. Fischer, TUM) for the acquisition of the LIFDI‐MS data. Furthermore, the authors thank M. Sc. Lukas Niederegger (Chair of Bioinorganic Chemistry, Prof. Hess, TUM) for his help concerning all technical aspects of the UV/Vis measurements. M. Sc. Philipp Keil (Dr. Terrance Hadlington, TUM) is acknowledged for the acquisition of variable temperature NMR data and Dr. W. Klein supported the crystallographic part. Open Access funding enabled and organized by Projekt DEAL. Publisher Copyright: © 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.

Keywords

Charge Transfer, Chromophore, Germanium Cluster, Laser Irradiation, Synthesis

DOI

10.1002/anie.202304088

Citation

Wallach, C, Selic, Y, Geitner, F S, Kumar, A, Thyrhaug, E, Hauer, J, Karttunen, A J & Fässler, T F 2023, ' Probing Charge-Transfer Processes in a Covalently Linked [Ge 9 ]-Cluster Imine Dyad ', Angewandte Chemie - International Edition, vol. 62, no. 29, e202304088 . https://doi.org/10.1002/anie.202304088

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https://urn.fi/URN:NBN:fi:aalto-202308164807

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[article-cris] Kemian tekniikan korkeakoulu / CHEM

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Probing Charge-Transfer Processes in a Covalently Linked [Ge9]-Cluster Imine Dyad

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