title: C,C'-bis(benzodiazaborolyl)dicarba-closo-dodecaboranes: synthesis, structures, photophysics and electrochemistry.
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 17,330 and 21,290 cm(-1) are typical for C,C'-bis(aryl)-ortho-carboranes, the observed low-energy emissions with Stokes shifts between 8320 and 15,170 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.
authors.affiliation: Fakultät für Chemie der Universität Bielefeld, 33615 Bielefeld, Germany. lothar.weber@uni-bielefeld.de
authors.forename: Lothar
authors.initials: L
authors.lastname: Weber
authors.forename: Jan
authors.initials: J
authors.lastname: Kahlert
authors.forename: Regina
authors.initials: R
authors.lastname: Brockhinke
authors.forename: Lena
authors.initials: L
authors.lastname: Böhling
authors.forename: Johannes
authors.initials: J
authors.lastname: Halama
authors.forename: Andreas
authors.initials: A
authors.lastname: Brockhinke
authors.forename: Hans-Georg
authors.initials: HG
authors.lastname: Stammler
authors.forename: Beate
authors.initials: B
authors.lastname: Neumann
authors.forename: Carlo
authors.initials: C
authors.lastname: Nervi
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Harder
authors.forename: Mark A
authors.initials: MA
authors.lastname: Fox