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Durham University

Department of Chemistry

Publication details for Dr Mark A. Fox

Weber, L., Kahlert, J., Brockhinke, R., Boehling, L., Brockhinke, A., Stammler, H.-G., Neumann, B., Harder, R. A. & Fox, M. A. (2012). Luminescence Properties of C-Diazaborolyl-ortho-Carboranes as Donor-Acceptor Systems. Chemistry - A European Journal 18(27): 8347-8357.

Author(s) from Durham

Abstract

Seven derivatives of 1,2-dicarbadodecaborane (ortho-carborane, 1,2-C2B10H12) with a 1,3-diethyl- or 1,3-diphenyl-1,3,2-benzodiazaborolyl group on one cage carbon atom were synthesized and structurally characterized. Six of these compounds showed remarkable low-energy fluorescence emissions with large Stokes shifts of 15100–20260 cm−1 and quantum yields (ΦF) of up to 65 % in the solid state. The low-energy fluorescence emission, which was assigned to a charge-transfer (CT) transition between the cage and the heterocyclic unit, depended on the orientation (torsion angle, ψ) of the diazaborolyl group with respect to the cage C[BOND]C bond. In cyclohexane, two compounds exhibited very weak dual fluorescence emissions with Stokes shifts of 15660–18090 cm−1 for the CT bands and 1960–5540 cm−1 for the high-energy bands, which were assigned to local transitions within the benzodiazaborole units (local excitation, LE), whereas four compounds showed only CT bands with ΦF values between 8–32 %. Two distinct excited singlet-state (S1) geometries, denoted S1(LE) and S1(CT), were observed computationally for the benzodiazaborolyl-ortho-carboranes, the population of which depended on their orientation (ψ). TD-DFT calculations on these excited state geometries were in accord with their CT and LE emissions. These C-diazaborolyl-ortho-carboranes were viewed as donor–acceptor systems with the diazaborolyl group as the donor and the ortho-carboranyl group as the acceptor.