Crystal structure of 8-hexyloxy-2-[(Z)-2-(naphthalen-2-yl)ethenyl]quinoline

In the title molecule, C27H27NO, the naphthalene and quinoline groups are both planar and subtend a dihedral angle of 15.47 (7)°. They are nearly coplanar with the cis-vinyl bridge and the hexyloxy chain, which adopts an all-trans conformation, resulting in transannular bifurcated intramolecular C—H⋯N,O contact. The crystal structure features γ-packing of the aromatic moieties, while the parallel packing of alkyl chains resembles that of alkanes.


Chemical context
In recent decades, -conjugated organic molecules with donor-acceptor architectures have received considerable attention regarding their diverse applications in organic optoelectronics and electronics, for example in non-linear optics and as organic semiconductors (Rao et al., 2010;Siram et al., 2011;Wang et al., 2015;Zhang et al., 2015). As for vinylbridged donor-acceptor molecules incorporating naphthalene as a donor and quinoline as an acceptor, the poor solubility (which hinders purification and processibility) is due to the good molecular coplanarity (Ishikawa & Hashimoto, 2011). The introduction of long substituents into quinoline or naphthalene cores is an effective method of solving this problem. Hexyloxy-substituted donor-acceptor molecules based on naphthalene and quinoline are a promising class owing to their satisfactory solubility. Moreover, the introduction of alkyl substituents of suitable length can not only increase the capacity for self-assembly, but also improve carrier mobility (Garnier et al., 1993;Halik et al., 2003). The title compound (1) was synthesized by a Wittig reaction and has been shown by single-crystal X-ray diffraction analysis to be a rare example of a stilbene-like donor--acceptor (D-Á Á ÁA) type molecule with a cis configuration, and the first structurally characterized cis-naphthalene-C C-quinoline derivative. The D-Á Á ÁA structure is known to favour highintensity two-photon absorption .

Supramolecular features
In the crystal, molecules related by b translation pack face-toface, forming strongly slanted stacks running along the b-axis direction (see Fig. 2). However,stacking between aromatic moieties (Hunter & Sanders, 1990) is practically absent. Thus, although the quinoline (Cg1) -systems are parallel, their overlap is marginal, involving only one carbon atom on either side, with a C10Á Á ÁC15(x, y + 1, z) contact distance of 3.540 (3) Å , while the naphthalene moiety overlaps with the alkyl chain of the next molecule. Molecules belonging to different stacks and related by a screw axis form a typicalmotif (Loots & Barbour, 2012), their quinoline and naphthalene moieties contact at an interplanar angle of 68.60 (5) . The packing of the n-hexyl chains resembles that of pure alkanes, with a parallel arrangement of the chains, which adopt an alltrans conformation.  Table 1 Hydrogen-bond geometry (Å , ). Symmetry code: (i) x; y À 1; z.

Figure 2
Crystal packing of compound (1). Hydrogen atoms are omitted for clarity.

Figure 1
Molecular structure of compound (1) with atom labelling. Atomic displacement ellipsoids are drawn at the 30% probability level. more planar conformation than the latter. In cis-2,5-bis(2methylbutoxy)-and cis-2,5-dibutoxy-1,4-bis[2-(pyrid-2-yl)vinyl]benzene (SIXQOH and SIXQUN; Liu et al., 2014), the (pyrid-2-yl)vinylbenzene fragments have a cis-configuration about the C C bond, but in both structures the pyridyl N atom is oriented outward, not intraannularly. Thus the pyridyl and benzene rings cannot be coplanar with the ethenyl bridge, due to the steric repulsion between ortho-H atoms, and are inclined to this bridge by 28-47 in a propeller-like fashion.
The C-C C bond angles in the vinyl bridge (129-131 ) are narrower than in (1).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. C-bound H atoms were refined using a riding model with C-H = 0.93-0.97 Å and U iso (H) = 1.2-1.5U eq (C), except for H27, which was refined in an isotropic approximation.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. 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 > 2sigma(F 2 ) is used only for calculating R-factors(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.