Crystal structure of N 1-phenyl-N 4-[(E)-(pyren-1-yl)methylidene]benzene-1,4-diamine

The title compound is non-planar, with the mean plane of the pyrene ring system and the terminal N-phenyl ring being inclined to the central p-phenylenediamine ring by 29.34 (4) and 43.43 (7)°, respectively. In the crystal, molecules are linked by a number of weak N—H⋯π, C—H⋯π and π–π interactions [inter-centroid distances = 3.5569 (11)–3.708 (1) Å], forming slabs lying parallel to (30).


Chemical context
Schiff bases often exhibit various biological activities, and in many cases have been shown to have antibacterial, anticancer, anti-inflammatory and antitoxic properties (Lozier et al., 1975). They are used as anion sensors (Dalapati et al., 2011), as non-linear optical compounds (Sun et al., 2012) and as versatile polynuclear ligands for multinuclear magnetic exchange clusters (Moroz et al., 2012). The pyrene unit is one of the most commonly used fluorophores due to its strong luminescence and chemical stability (Aoki et al., 1991;Nishizawa et al., 1999;van der Veen et al., 2000). Another interesting feature of the pyrene unit is theinteraction between pyrene aromatic rings in the crystal packing, which can permit the formation of highly ordered molecular aggregates in the solid state by architecturally controlled selfassembly (Desiraju et al., 1989;Munakata et al., 1994). Pyrene is a commonly used fluorophore due to its unusual fluorescent properties: intense fluorescence signals, vibronic band dependence with the media (Karpovich & Blanchard, 1995), and use in fluorescence sensors (Bell & Hext, 2004) and excimer formation (Lodeiro et al., 2006). As a result of these particular properties and because of its chemical stability, it is also employed as a probe for solid-state studies (Corma et al., 2002) and polymer association (Seixas de Melo et al., 2003). We report herein on the crystal structure of the title compound, synthesized by the condensation reaction of 1-pyrenecarboxaldehyde and N-phenyl-p-phenylenediamine.

Synthesis and crystallization
80 mg (0.435 mmol) of N-phenyl-p-phenylenediamine were dissolved in 10 ml of absolute ethanol. To this solution, 100 mg (0.435 mmol) of pyrene-1-carbaldehyde in 5 ml of absolute ethanol was added dropwise under stirring. The mixture was stirred for 10 min, two drops of glacial acetic acid were then added and the mixture was further refluxed for 2h. The resulting yellow precipitate was recovered by filtration, washed several times with small portions of ice-cold ethanol and then with diethyl ether to give 150 mg (87%) of the title compound. Yellow block-like crystals suitable for X-ray analysis were obtained within 3 days by slow evaporation of a solution in MeOH. The molecular structure of the title compound, showing the atom labelling. Displacement ellipsoids are drawn at the 40% probability level. Table 1 N-HÁ Á Á and C-HÁ Á Á interactions (Å , ).
Cg5 and Cg6 are the centroids of the C20-C24/C29 and C24-C29 rings, respectively, in the pyrenyl ring system.

Figure 2
A view along the b axis of the zigzag chain in the crystal of the title compound. The C-HÁ Á Á and N-HÁ Á Á interactions are shown as dashed lines (see Table 1 for details).

Figure 3
A view along the b axis of the crystal packing of the title compound. The C-HÁ Á Á, N-HÁ Á Á andinteractions are shown as dashed lines (see Table 1 for details).

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. 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 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.