(E)-3-(Biphenyl-4-yl)-1-(3-bromophenyl)prop-2-en-1-one

In the title compound, C21H15BrO, there are two planar rings connected through a conjugated double bond. As it crystallizes in a non-centrosymmetric space group it can be regarded as a good candidate for non-linear optical applications. The molecule adopts an E configuration and the C—C=C—C torsion angle is 177.1 (4)°. The overall conformation of the compound may be described by the values of dihedral angles between the approximately planar parts. The terminal rings are twisted by an angle of 51.52 (9)°, while the biphenyl part is almost planar, the dihedral angle between the planes of the rings being 4.44 (17)°. The unit cell has one long dimension, above 35 Å, characteristic also of a majority of related compounds. The molecules pack head-to-tail along this direction. C—H⋯π interactions are observed in the crystal structure.

In the title compound, C 21 H 15 BrO, there are two planar rings connected through a conjugated double bond. As it crystallizes in a non-centrosymmetric space group it can be regarded as a good candidate for non-linear optical applications. The molecule adopts an E configuration and the C-C C-C torsion angle is 177.1 (4) . The overall conformation of the compound may be described by the values of dihedral angles between the approximately planar parts. The terminal rings are twisted by an angle of 51.52 (9) , while the biphenyl part is almost planar, the dihedral angle between the planes of the rings being 4.44 (17) . The unit cell has one long dimension, above 35 Å , characteristic also of a majority of related compounds. The molecules pack head-to-tail along this direction. C-HÁ Á Á interactions are observed in the crystal structure.

Comment
For such a structurally simple group of compounds, chalcones have displayed an impressive array of biological activities, among which antimalarial (Liu et al., 2003), antiprotozoal (Nielson et al., 1998), nitric oxide inhibition (Rajas et al., 2002) and anticancer (Dinkova-Kostova et al., 1998) activities have been cited in the literature. Also, among organic compounds reported for non-linear optical (NLO) properties, chalcone derivatives are notable materials for their excellent blue-light transmittance and good crystallizability. They provide the necessary configuration to show NLO properties, with two planar rings connected through a conjugated double bond (e.g., Sarojini et al., 2006). Substitution on either of the benzene rings greatly influences the non-centrosymmetric crystal packing. It is speculated that, in order to improve the activity, more bulky substituents should be introduced to increase the spontaneous polarization of non-centrosymmetric crystals (Fichou et al., 1988). The molecular hyperpolarizability is strongly influenced, not only by the electronic effect, but also by the steric effect of the substituent (Cho et al., 1996). Prompted by this, and in a continuation of our quest to synthesize new materials which can find use in the photonics industry, we have synthesized new chalcones and studied their SHG (second harmonic generation) efficiency.

(2E)-3-(biphenyl-4-yl)-1-(3-bromophenyl)prop-2-en-1-one (I) crystallizes in the non-centrosymmetric space group
Pca2 1 , which makes NLO activity possible. The overall conformation of the molecule can be described by the dihedral angles between the planar fragments: two rings of biphenyl system (A and B, cf. Fig. 1), the enone fragment (C) and the (bromo)phenyl ring (D). All these fragments are in a good approximation planar (maximum deviation from the least-squares plane is 0.018 (4)Å for the enone fragment). The biphenyl rings are almost coplanar, the dihedral angle between them is 4.44 (17)°; the enone fragment is significantly inclined with respect to both neighbouring rings, B/C angle is 30.74 (11)°a nd C/D -16.34 (12)°.
In general, the conformation of the molecule (I) is similar to the related compounds (e.g., Fischer et al., 2007a, b, c, Moorthi et al., 2007. The unit cell of (I) has a long c axis of 36.619 (2) Å, and the molecules pack head-to-tail along this direction (Fig. 2).
Such a long unit-cell parameter is observed in a number of similar compounds, even though they crystallize in different space groups and even in different crystal classes. For instance, 4-bromo (Fischer et al., 2007b), 4-chloro (Fischer et al., 2007a) and 4-methoxyphenyl (Fischer et al., 2007c analogues crystallize all in the Cc space groups with the long parameter (ca. 36 Å) along c-direction, 4-fluoro derivative (Sarojini et al., 2007) -in P2 1 space group (Z' = 2) with the long b direction etc. It might be also noted, that other unit-cell parameters in all these structures are also similar to those observed in (I), and the comparison of the packing modes shows a significant degree of isostructurality. This suggests that the same interactions are responsible for the crystal packing in these structures: these can be some relatively short and linear C-H···π contacts, and van der Waals interactions. supplementary materials sup-2 Experimental 5 ml 40% KOH solution was added to a thoroughly stirred solution of 3-bromoacetophenone (1.0 g, 5 m mol) and 4-biphenylcarboxaldehyde (1.0 g, 5.4 m mol) in 15 ml of methanol. The mixture was stirred overnight and filtered. The product formed was crystallized in methanol. X-ray quality crystals were grown from slow evaporation of ethyl acetate solution (m.p.: 378 -380 K).

Refinement
Hydrogen atoms were placed in idealized positions, and refined as riding. Their isotropic thermal parameters were set at 1.2 times U eq 's of appropriate carrier atoms. Fig. 1. Anisotropic ellipsoid representation of the compound I together with atom labelling scheme. The ellipsoids are drawn at 50% probability level, hydrogen atoms are depicted as spheres with arbitrary radii.  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 > σ(F 2 ) is used only for calculating Rfactors(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.