1-(4-{[(1,3,3-Trimethylindolin-2-ylidene)methyl]diazenyl}phenyl)ethanone

The title compound, C20H21N3O, has crystallographic mirror symmetry with all non-H atoms apart from the methyl C atom of the CMe2 group lying on the mirror plane. Molecules are linked into planar sheets parallel to (010) by phenyl–azo C—H⋯N and phenyl–ethanone C—H⋯O interactions. Methyl C—H⋯π interactions provide crosslinking between the planes.

The title compound, C 20 H 21 N 3 O, has crystallographic mirror symmetry with all non-H atoms apart from the methyl C atom of the CMe 2 group lying on the mirror plane. Molecules are linked into planar sheets parallel to (010) by phenyl-azo C-HÁ Á ÁN and phenyl-ethanone C-HÁ Á ÁO interactions. Methyl C-HÁ Á Á interactions provide crosslinking between the planes.
However, despite the vast range of possibilities, there are some strategies for designing effective NLO materials that consistently give good results, including the incorporation of azo linkers into the conjugated interconnect. Consequently, a number of such D-azo-A systems have been investigated, with many azo-containing systems showing improved nonlinear optical performance and thermal stability (Zhang et al., 1997) when compared to the olefinic analogues.
Furthermore, over the past two decades, azobenzene/azoheterocycle containing polymers have been the subject of intensive research in optical switching, and digital and holographic storage applications (Prim et al., 1994). Thus, they represent a useful class of compound to study as they hold promise for applications beyond just non-linear optics. Hence, there is a need to synthesize new organic NLO materials with azo linkers and study their structural, physical, thermal and optical properties. We have recently reported a range of NLO materials containing an azo linker (Ashraf et al., 2013).
The asymmetric unit contains the title compound which lies on a crystallographic mirror plane (Fig. 1). The planarity of structures containing an azo linkage and indeed, the N-N bond length, varies considerably depending on the bound ring systems (Allen, 2002; CSD Version 5.34, with May 2013 updates). For example in LAQYAE (Odabasoglu et al., 2005) the dihedral angles of the pendant phenyl rings being 0.31 (12) and 26.74 (14)° for the two independent molecules with N-N lengths of 1.158 (4) and 1.247 (3) Å, respectively. The closest related structure with appended phenyl and alkene chain is ULEGAT (Simunek et al., 2003) with a comparable N-N length of 1.282 (2) Å, and dihedral angle 0.4 (2)°. The quality of the crystal packing & consequent diffraction data confirms that the methyl hydrogen atoms based on the inplane carbon C11 are ordered unlike the disorder model required for the related compound 2 (Bhuiyan et al., 2011), hereafter FATN, which also The planar molecules in the title compound form sheets utilizing two interactions in a similar way although with different interactions to those in FATN. Here, the phenyl(C14)-H14···N3(azo) interaction provides one of the in-plane links making the common R 2 2 (8) motif (Bernstein et al., 1995) parallel to ethene(C)-H···N3(cyano) R 2 2 (16) interaction in FATN, aligned around a two fold axis of symmetry (Fig. 2). Likewise, a second in-plane interaction here occurs between phenyl(C2)-H and the ketone oxygen O1 described by the C(14) motif whilst in FATN a (dichloromethane)C-Cl···N(cyano) interaction performs the same role. A methylC-H···O(ketone) interaction is also found in the ULEGAT crystal packing. The planar (0 1 0) sheets are then cross-linked by two (symmetric) methyl(C11)-H11A···π(phenyl) interactions as shown in Fig. 2

Refinement
All H atoms except those on C11 & C20 bound to carbon were constrained to their expected geometries (C-H 0.95-0.98 Å). The methyl-H atoms bound to atoms on the mirror plane were located on difference Fourier maps and their positions refined. All methyl-and phenyl-H atoms were refined with U iso 1.5 & 1.2 times, respectively, that of the U eq of their parent atom.