(1E,4E)-1,5-Bis[4-(diethylamino)phenyl]penta-1,4-dien-3-one

There are two crystallograpically independent molecules in the asymmetric unit of the title bischalcone derivative, C25H32N2O. Both molecules are twisted with a dihedral angle between the two substituted benzene rings of 11.19 (16)° in one molecule and 14.40 (15)° in the other. The central penta-1,4-dien-3-one fragments make dihedral angles of 8.49 (17) and 4.26 (17)° with the two adjacent benzene rings in one molecule, whereas the corresponding values are 8.42 (16) and 6.18 (16)° in the other. In the crystal, molecules are arranged into chains along the c-axis direction. Adjacent chains are inter-linked by weak intermolecular C—H⋯O interactions. The crystal is further stabilized by C—H⋯π interactions.

There are two crystallograpically independent molecules in the asymmetric unit of the title bischalcone derivative, C 25 H 32 N 2 O. Both molecules are twisted with a dihedral angle between the two substituted benzene rings of 11.19 (16) in one molecule and 14.40 (15) in the other. The central penta-1,4-dien-3-one fragments make dihedral angles of 8.49 (17) and 4.26 (17) with the two adjacent benzene rings in one molecule, whereas the corresponding values are 8.42 (16) and 6.18 (16) in the other. In the crystal, molecules are arranged into chains along the c-axis direction. Adjacent chains are inter-linked by weak intermolecular C-HÁ Á ÁO interactions. The crystal is further stabilized by C-HÁ Á Á interactions.
Supporting information for this paper is available from the IUCr electronic archives (Reference: SJ5396).

Comment
Mono-carbonyl analogues of curcumin are an important class of compounds due to their variety of properties. For example these compounds exhibit anti-inflammatory (Zhao et al., 2010), antimalarial (Wanare et al., 2010), antitumor (Shibata et al., 2009) and anti-oxidant properties (Weber et al., 2005). They also act as dye sensitizers (Barnabas et al., 1992) and fluorescence agents (Makarov et al., 2012). These analogues were designed to counteract some of the disadvantageous properties of curcumin such as its poor bioavailability and instability in neutral to basic conditions. We have previously reported the crystal structures of (1E,4E)-1,5-bis(2,4,5-trimethoxyphenyl)penta-1,4-dien-3-one (I) (Fun et al., 2010) and (1E,4E)-1,5-bis(2,4,6-trimethoxyphenyl)penta-1,4-dien-3-one (II) (Ruanwas et al., 2011). The title compound (III) is one of the mono-carbonyl analogues of curcumin designed and synthesized by our group to study antityrosinase activity and its fluorescence properties. It was found that the title compound exhibits fluorescence properties with an orange fluorescence color which will be reported elsewhere with its closely related compounds, it also possesses anti-tyrosinase activity by the dopachrome method with an IC 50 value of 0.018 mg ml -1 . We reported herein the crystal structure of (III).
There are two crystallographically independent molecules A and B in the asymmetric unit of (III) ( Fig. 1) with the same conformation but slight differences in bond angles. The molecular structure of (III), C 25 H 32 N 2 O is unsymmetrical and twisted. The dihedral angle between the C1-C6 and C12-C17 benzene rings is 11.19 (16)° in molecule A (Fig. 2a) whereas it is 14.40 (15)° in molecule B. The central penta-1,4-dien-3-one unit (C7-C11/O1) is planar with r.m.s.  (Allen et al., 1987) and are comparable with those found in related structures (Fun et al., 2010;Harrison et al., 2006 andRuanwas et al., 2011).
In the crystal packing (Fig. 2), the molecules are arranged into chains along the c axis and the adjacent chains are further linked by weak C-H···O interactions ( Table 1). The crystal is further stabilized by weak intermolecular C-H···π interactions (Table 1). Interestingly there are only one C-H···O and two C-H···π interactions stabilising the structure of (III). This contrasts sharply with the packing for (I) and (II) where significantly more weak C-H···O and C-H···π interactions were observed (Fun et al., 2010 andRuanwas et al., 2011).

Experimental
The title compound was synthesized by mixing 4-diethylaminobenzaldehyde (0.90 g, 6 mmol) and acetone (0.25 ml, 3 mmol) in ethanol (30 ml). 30% NaOH aqueous solution (5 ml) was then added and the mixture was stirred at room temperature for 2 h, The resulting orange solid obtained was collected by filtration, washed with distilled water and dried.
Orange block-shaped single crystals of the title compound were grown in ethanol by slow evaporation, Mp. 440-441 K.

Refinement
All H atoms were positioned geometrically and allowed to ride on their parent atoms, with d(C-H) = 0.93 Å for aromatic and CH; 0.96 Å for CH 3 atoms. The U iso values were constrained to be 1.5U eq of the carrier atom for methyl H atoms and 1.2U eq for the remaining H atoms. A rotating group model was used for the methyl groups. The same U ij parameters were used for atom pairs N1A/C18A and N2B/C22B.

Figure 1
The molecular structure of the title compound, drawn with 30% probability displacement ellipsoids and the atomnumbering scheme.
Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.