Luminescence Properties of C-Diazaborolyl-ortho-Carboranes as Donor-Acceptor Systems

Weber, L.; Kahlert, J.; Brockhinke, R.; Boehling, L.; Brockhinke, A.; Stammler, H.-G.; Neumann, B.; Harder, R.A.; Fox, M.A.

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.

Citation

Weber, L., Kahlert, J., Brockhinke, R., Boehling, L., Brockhinke, A., Stammler, H., …Fox, M. (2012). Luminescence Properties of C-Diazaborolyl-ortho-Carboranes as Donor-Acceptor Systems. Chemistry - A European Journal, 18(27), 8347-8357. https://doi.org/10.1002/chem.201200390

• Journal Article Type: Article
• Publication Date: Jul 2, 2012
• Deposit Date: May 2, 2013
• Journal: Chemistry - A European Journal
• Print ISSN: 0947-6539
• Electronic ISSN: 1521-3765
• Publisher: Wiley
• Peer Reviewed: Peer Reviewed
• Volume: 18
• Issue: 27
• Pages: 8347-8357
• DOI: https://doi.org/10.1002/chem.201200390
• Keywords: Carboranes, Charge transfer, Diazaboroles, Donor–acceptor systems, Luminescence.
• Public URL: https://durham-repository.worktribe.com/output/1457551