(E)-1-(4-Bromophenyl)-2-(4-tert-butylphenyl)-1-phenylethene

In the structure of the title compound, C24H23Br, the configuration about the double bond is E. The dihedral angles between the tert-butyl-substituted benzene ring and the unsubstituted and Br-substituted rings are 57.1 (2) and 78.2 (2)°, respectively. The methyl groups are disordered over two positions; the site occupancy factors are ca 0.8 and 0.2.

In the structure of the title compound, C 24 H 23 Br, the configuration about the double bond is E. The dihedral angles between the tert-butyl-substituted benzene ring and the unsubstituted and Br-substituted rings are 57.1 (2) and 78.2 (2) , respectively. The methyl groups are disordered over two positions; the site occupancy factors are ca 0.8 and 0.2.

Comment
Stilbene derivatives are attracting much attention due to their photoluminescent properties (Mooney et al., 1984). Stilbenes, short sub-units of PPV compounds that are important as the emissive layer of organic light-emitting diodes (Kraft et al., 1998), have also been of wide interest in research to gain an understanding of the light emission mechanisms and to predict the influence of substitution on the emitted light (Martin & Diederich, 1999). The title compound (I) was prepared as an important intermediate for such studies by the reaction of 4-bromobenzophenone and diethyl 4-methylbenzylphosphonate using potassium tert-butoxide as the base. The reaction produced a 60:40 mixture of (Z)-and (E)-stereoisomers (Scheme 1). The initial recrystallization process from 2-propanol solution allowed the selective crystallization of the (Z)-isomer (II).
The title isomer (I) was obtained by consecutive recrystallizations of the remaining mixture from 2-propanol.

Experimental
To the mixture of 4-tert-butylbenzyl phosphonate (35.1 mmol, 9.98 g) and potassium tert-butoxide (54.0 mmol, 6.06 g) in THF (54 ml) was added a solution of 4-bromobenzophenone (27.0 mmol, 5.00 g) in THF (200 ml) at room temperature under an Ar atmosphere. The mixture was stired at refluxing temperature for 3 h. The reaction mixture was cooled to room temperature, diluted with ethyl acetate (300 ml), washed with 1% aqueous HCl (200 ml), water (300 ml) and brine, dried over MgSO 4 , and concentrated in vacuo. The crude product, which was a 60:40 mixture of (Z)-and (E)-stereoisomers by GC analysis, was initially recrystallized from 2-propanol solution to generate the (Z)-isomer (II) as pure crystals. The title isomer (I) was obtained by the consecutive recrystallization of the remaining mixture from 2-propanol solution.

Refinement
The H atoms were included in their idealized positions and refined riding on the corresponding C atoms with C-H = 0.93 to 0.96 Å, and with U iso = 1.2U eq (C) or 1.5U eq (C) for methyl-H. The methyl groups of the tert-butyl residue were found to be disordered over two positions and from refinement, the major component had a site occupancy factor = 0.791 (17).