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Probing Charge-Transfer Processes in a Covalently Linked [Ge9]-Cluster Imine Dyad
Authors:Dr Christoph Wallach  M?Sc Yasmin Selic  Dr Felix S Geitner  Ajeet Kumar  Dr Erling Thyrhaug  Prof?Dr Jürgen Hauer  Prof?Dr Antti J Karttunen  Prof?Dr Thomas F Fässler
Institution:1. TUM School of Natural Sciences, Department Chemie, Technische Universität München, Lichtenbergstraße 4, 85747 Garching, Germany;2. Department of Chemistry and Materials Science, Aalto University, 00076 Aalto, Finland
Abstract: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.
Keywords:Charge Transfer  Chromophore  Germanium Cluster  Laser Irradiation  Synthesis
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