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Durham University

Department of Chemistry

Publication details for Dr Mark A. Fox

Weber, L., Kahlert, J., Brockhinke, R., Böhling, L., Halama, J., Brockhinke, A., Stammler, H.-J., Neumann, B., Nervi, C., Harder, R.A. & Fox, M.A. (2013). C,C′-Bis(benzodiazaborolyl)dicarba-closo-dodecaboranes: Synthesis, structures, photophysics and electrochemistry. Dalton Transactions 42(30): 10982-10996.

Author(s) from Durham

Abstract

Six new C,C′-bis(benzodiazaborolyl)dicarba-closo-dodecaboranes, 1,A-R2-1,A-C2B10H10, where R represents the group 2-(1,3-Et2-1,3,2-N2BC6H4) or 2-(1,3-Ph2-1,3,2-N2BC6H4) and A is 2, 7 or 12, were synthesized from o-, m-, and p-dicarbadodecaboranes (carboranes) by lithiation and subsequent treatment with the respective 2-bromo-1,3,2-benzodiazaboroles. UV-visible and fluorescence spectra of all carboranes display low energy charge transfer emissions. While such emissions with Stokes shifts between 17330 and 21290 cm−1 are typical for C,C′-bis(aryl)-ortho-carboranes, the observed low-energy emissions with Stokes shifts between 8320 and 15170 cm−1 for the meta- and para-isomers are unusual as high-energy emissions are typical for meta- and para-dicarbadodecaboranes. Fluorescence quantum yields (ϕF) for the novel 1,7- and 1,12-bis(benzodiazaborolyl)-carboranes depend on the substituents at the nitrogen atoms of the heterocycle. Thus, the para-carborane with N-ethyl substituents 1,12-(1′,3′-Et2-1′,3′,2′-N2BC6H4)2-1,12-C2B10H10 has a ϕF value of 41% in cyclohexane solution and only of 9% in the solid state, whereas the analogous 1,12-(1′,3′-Ph2-1′,3′,2′-N2BC6H4)2-1,12-C2B10H10 shows quantum yields of 3% in cyclohexane solution and 72% in the solid state. X-ray crystallographic, computational and cyclic voltammetry studies for these carboranes are also presented.