Crystal structure of (E)-1,2-bis(6-bromo-9-hexyl-9H-carbazol-3-yl)ethene

In the title compound, the two carbazole groups are nearly coplanar, making a dihedral angle of 16.90 (5)°, and are bridged by vinyl. The crystal structure features π–π and C—H⋯π interactions and C—H⋯Br short contacts.


Chemical context
To date, -conjugated organic molecules have attracted considerable attention because of their applications in many fields, such as non-linear optics (Kim et al., 2016;Percino et al., 2016;Xue et al., 2014) and optoeletronic devices (Shi et al., 2016;Zhang et al., 2015). Carbazole-based -conjugated compounds have been utilized as the light-emitting layers in OLEDs (Liu et al., 2006. The design of the title molecule combines the advantages of several factors. Firstly, vinyl has been introduced to bridge molecules; this is of importance for extension of the -conjugated system, which is beneficial for carrier mobility (Wang et al., 2012). Secondly, introducing long alkyl substituents to carbazole cores is an effective method to solve poor solubility (Teetsov & Fox, 1999) and fluorescence quenching in the solid state (Hua et al., 2015). In addition, introduction of Br into the structure of vinyl-bridged carbazoles can enhance intermolecular interactions by forming non-classical hydrogen bonds. Br-substituted molecules are excellent intermediate products since the bonding energy of the C-Br bond is weaker than that of C-H, and Br substituents are easily replaced by other substituents. ISSN 2056-9890

Structural commentary
The title compound crystallizes in the space group P ı " with one molecule in the asymmetric unit, as shown in Fig. 1. The molecule is an (E) isomer and has approximate C s symmetry. The mean deviation from the plane of the cabazole unit including N1 is 0.0272 Å , with deviations of 0.159 (2) Å for C11 and 0.059 (2) Å for Br1, while the mean of the cabazole unit including N2 is 0.0224 Å with deviations of 0.052 (2) Å for C12 and 0.084 (2) Å for Br2. Note that there is a double bond between carbon atoms C11 and C12. Each carbazole group is planar, excluding hexyl groups, and its respective peripheral atoms such as bromine and the double-bonded carbon atoms were accommodated in a planar geometry, as shown by the C6-N1-N2-C17 torsion angle of À147.5 (2) and the Br1-C25-C32-Br2 torsion angle of À167.70 (3) . The two carbazole groups are almost in the same plane, making a dihedral angle of 16.9 (5) . The angles between the leastsquares planes of neighboring rings are in the range of 1.00-1.42 . Furthermore, they are trans to the C C double bond, as indicated by the C10-C11-C12-C13 torsion angle of 176.1 (2) . The intramolecular Br1Á Á ÁBr2 distance of 16.710 (5) Å is much longer than the sum of the van der Waals radii (3.7 Å ) and the angle between C-Br bonds is 169.4 , indicating that the title molecule forms an extended, conjugated -system.

Database survey
A search of the Cambridge Crystallographic Database (WebCSD, Version 1.1.2, last update November 2016; Groom et al., 2016) for (E)-1,2-di(9H-carbazol-3-yl)ethene, reveals six structures. The structure of (E)-1,2-bis(9-hexyl-9H-carbazol-3yl)ethene was determined successfully by our research group (Shi, Liu, Dong et al., 2012;Shi, Liu, Guo et al., 2012) and we have also investigated the propeller-shaped structures of two ethene derivatives substituted by carbazole, phenyl and dimesitylboron (Shi et al., 2016). The single crystal structure of the ethene substituted by two cabazole groups and two phenyl rings has been reported  as well as structures where the two carbazole groups are linked via several organic groups, including vinyl (Kumar et al., 2006;Song et al., 2008). The crystal packing of the title compound 1 viewed along the b axis. Details of C-HÁ Á ÁBr also were showed. Table 1 Hydrogen-bond geometry (Å , ).

Figure 1
The molecular structure of the title compound, 1, with the atom labelling. Displacement ellipsoids are drawn at the 30% probability level.

Funding information
SHELXTL (Bruker, 2005). Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.