(Z)-3-(9-Anthryl)-1-(2-thienyl)prop-2-en-1-one1

There are two crystallographically independent molecules in the asymmetric unit of the title heteroaryl chalcone, C21H14OS: the dihedral angle between the thiophene and anthracene rings is 75.07 (17)° in one molecule and 76.32 (17)° in the other. The crystal structure is consolidated by short C⋯O [3.348 (5)–3.394 (5) Å], C⋯S [3.607 (5)–3.666 (5) Å] and S⋯O [2.926 (3) Å] contacts, as well as by C—H⋯π and π–π interactions [Cg⋯Cg = 3.745 (3) Å].


Comment
Chalcones have been studied for their chemical and biological activities for a long time. They have a wide range of applications such as in non-linear optical (NLO) materials (Patil & Dharmaprakash, 2008), fluorescent materials (Svetlichny et al., 2007) and for showing various biological activities (Saydam et al., 2003). The anthracene moieties are well known for their high absorption co-efficients as well as their high fluorescence yields (Oliveira et al., 2007). These interesting properties has lead us to synthesize the title heteroaryl chalcone derivative, (I), which contains the donor sub-unit (anthracene) and fluorophore (thiophene) in order to study its NLO and fluorescent properties. We have previously synthesized and reported the crystal structures of chalcones and heteroaryl chalcone derivatives (Chantrapromma et al., 2009;Suwunwong et al., 2009a, b) which exist in the E configuartion. Herein, we report the crystal structure of the (I) which is in the Z configuration.
Compound (I) crystallizes in the non-centrosymmetric orthorhombic space group Pna2 1 and therefore, it should exhibit second-order nonlinear optical properties. Moreover, (I) also shows interesting fluorescence properties which will be reported elsewhere.
The asymmetric unit of (I) contains two molecules, A and B, with the same configuration but with slight differences in bond lengths and angles. The molecule of (I)(  (Chantrapromma et al., 2009;Suwunwong et al., 2009a, b).

Experimental
Compound (I) was synthesized by the condensation of anthracene-9-carbaldehyde (2 mmol, 0.41 g) with 2-acetylthiophene (2 mmol, 0.22 ml) in ethanol (30 ml) in the presence of NaOH (5 ml, 30 %). After stirring for 2 h, a yellow solid appeared which was then collected by filtration, washed with distilled water, dried and purified by repeated recrystallization using ethanol/acetone in a 1:5 ratio as solvent. Orange block-shaped crystals of (I) were obtained from hot ethanol by the slow evaporation of the solvent held at room temperature for several days; M.p. 391-392 K.

Refinement
All H atoms were placed in calculated positions with C-H = 0.93 Å and U iso = 1.2U eq (C). The highest residual electron density peak was located 0.14 Å from atom C19B and the deepest hole was located 0.48 Å from atom S1B.
Figures Fig. 1. The molecular structure of (I), showing 50% probability displacement ellipsoids and the atom-numbering scheme.