2,7-Dibromo-9,9-dimethyl-9H-fluorene

The title molecule, C15H15Br2, has crystallographic m2m site symmetry. As a result, all atoms, except for those of the methyl groups, are exactly coplanar. In the crystal structure, there are weak π–π interactions with a centroid–centroid distance of 3.8409 (15) Å between symmetry-related molecules, which stack along the c axis.

The title molecule, C 15 H 15 Br 2 , has crystallographic m2m site symmetry. As a result, all atoms, except for those of the methyl groups, are exactly coplanar. In the crystal structure, there are weakinteractions with a centroid-centroid distance of 3.8409 (15) Å between symmetry-related molecules, which stack along the c axis.

Comment
Because of their good thermal and chemical stability along with high emission efficiency, fluorene derivatives have shown many applications as electronic materials, especially for organic light emitting diodes (OLEDs) (Holder et al., 2005;Kulkarni et al., 2004;Seneclauze et al., 2007;Padmaperuma et al., 2006;Tsuboyama et al., 2003). In this regard, small molecules, oligomers, or polymers with the 9,9-dialkylfluorene subunit possess interesting emissive properties. The quality and efficiency of such OLEDs have been shown to depend crucially on the stacking mode of the fluorene motif. On the other hand, the selected alkyl groups with different lengths or branched alkyl chains have a deep influence on the property and the packing mode of fluorene-based molecules (Scherf & List, 2002). During our study on such OLEDs crystalline materials, the crystal structure of the title compound has been determined in order to elucidate its molecular conformation and packing mode, which may be useful for further understanding its properties.
The molecular structure of the title compound is shown in Fig. 1. The complete molecule is generated two mirror planes which intersect each other [ crystallographic m2m site symmetry]. As a result, all the carbon atoms [except for those of the methyl groups] and the bromide atoms are exactly co-planar. In the crystal structure, weak π-π interactions between symmetry related benzene rings [C1-C6] with a centroid to centroid distance of 3.8409 (15) Å and perpendicular distance of 3.456 (1) Å form a one-dimensional chain along the c axis (see Fig. 2).

Experimental
The title compound was prepared according to the literature method (Belfield et al., 2000). Single crystals suitable for X-ray diffraction were obtained by recrystallization of a solution of the title compound in a mixture of ethyl acetate and petroleum ether.

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 , convention-