Synthesis and crystal structure of 2-(anthracen-9-yl)-1-(tert-butyl-dimethyl-sil-yl)-3,6-di-hydro-1λ4,2λ4-aza-borinine.

The title compound, C24H30BNSi (I), is an asymmetric 1,2,3,6-tetra-hydro-1,2-aza-borinine consisting of a BN-substituted cyclo-hexa-diene analog with a B-anthracenyl substituent. A ring-closing metathesis with subsequent substitution of the obtained BCl 1,2-aza-borinine using anthracenyl lithium yielded the title compound I. The asymmetric unit (Z = 8) belongs to the ortho-rhom-bic space group Pbca and shows an elongated N-C bond compared to previously reported BN-1,4-cyclo-hexa-diene [Abbey et al. (2008 ▸) J. Am. Chem. Soc. 130, 7250-7252]. The primarily contributing surface inter-actions are H⋯H and C⋯H/H⋯C (as elucidated by Hirshfeld surface analysis) which are dominated by van der Waals forces. Moreover, the non-aromatic BN heterocycle and the protecting group exhibit intra- and inter-molecular C-H⋯π inter-actions, respectively, with the anthracenyl substituent.

BN-Substitution in Dithienylpyrenes Prevents Excimer Formation in Solution and in the Solid State.

Boron-nitrogen substitutions in polycyclic aromatic hydrocarbons (PAHs) have a strong impact on the optical properties of the molecules due to a significantly more heterogeneous electron distribution. However, besides these single-molecule properties, the observed optical properties of PAHs critically depend on the degree of intermolecular interactions such as π-π-stacking, dipolar interactions, or the formation of dimers in the excited state. Pyrene is the most prominent example showing the latter as it exhibits a broadened and strongly bathochromically shifted emission band at high concentrations in solution compared to the respective monomers. In the solid state, the impact of intermolecular interactions is even higher as it determines the crystal packing crucially. In this work, a thiophene-flanked BN-pyrene (BNP) was synthesized and compared with its all-carbon analogue (CCP) in solution and in the solid state by means of crystallography, NMR spectroscopy, UV-vis spectroscopy, and photoluminescence (PL) spectroscopy. In solution, PL spectroscopy revealed the solvent-dependent presence of excimers of CCP at high concentrations. In contrast, no excimers were found in BNP. Clear differences were also observed in the single-crystal packing motifs. While CCP revealed overlapped pyrene planes with centroid distances in the range of classical π-stacking interactions, the BNP scaffolds were displaced and significantly more spatially separated.

High molecular weight poly(N-methyl-B-vinylazaborine) - a semi-inorganic B-N polystyrene analogue.

We present the synthesis of a B-N analogue of polystyrene, poly(N-methyl-B-vinylazaborine) in high molecular weight (MW = 24.9 kDa). Furthermore, it was possible to prepare a copolymer with the C-C analogue. A thorough comparison between the polymers by NMR spectroscopy, TGA, DSC and GPC showed significant differences between these polymers.