2-{[(Biphenyl-2-yl)diazen-yl]methyl-idene}-1,3,3-trimethyl-indoline.

The title molecule, C24H23N3, shows some delocalization of charge based on the small [8.0 (2)°] angle between the indolin-2-ylidene ring system and the link methyldiazene C2N2 atom plane. A further twist of 17.2 (3)° is subtended between the C2N2 plane and its attached benzene ring. The dihedral angle between the biphenyl rings is 47.96(14)°. In the crystal, the molecules pack via C—H⋯π attractive interactions.

The title molecule, C 24 H 23 N 3 , shows some delocalization of charge based on the small [8.0 (2) ] angle between the indolin-2-ylidene ring system and the link methyldiazene C 2 N 2 atom plane. A further twist of 17.2 (3) is subtended between the C 2 N 2 plane and its attached benzene ring. The dihedral angle between the biphenyl rings is 47.96(14) . In the crystal, the molecules pack via C-HÁ Á Á attractive interactions.
Cg1, Cg2 and Cg3 are the centroids of the C19-C24, C4-C9 and C13-C18 rings, respectively. coefficients and their absorption maxima can usually be tailored to lie anywhere in the visible region via appropriate substitution onto the phenyl rings. Furthermore due to their geometrically rigid structures and large aspect ratios, azobenzene compounds are ideal as mesogens (Möhlmann & van der Vorst, 1989).

D-HÁ
Recently, we have become interested in developing photoswitchable molecules in order to alter the refractive index of a given material via photo-induced rather than electrically induced means (as occurs in nonlinear optical materials). As part of this we have been exploring how the placement of different substituents (e.g. donors, acceptors or neutral) on the backbone of various azo dyes affects the speed and reversibility of the photo-and thermal isomerization processes. Included in these studies have been a suite of compounds containing an indoline donor, an azo linker and a variety of substituents attached to the terminal nitrogen atom of the azo moiety. The molecules are easily prepared via diazotization of the corresponding aryl amine of the terminal substituent and coupling of the resultant diazonium salt with Fisher's base. The reaction is exemplified in Fig. 1 using 2-aminobiphenyl, 1, as the aromatic amine and which yielded the title compound, 3, in 80% yield. and YADTIH (Jones & Chrapkowski (2004)]. In these latter three compounds, where only a phenyl (or para-substituted phenyl) ring was bound to N3, an additional indol-2-ylidene ring was bonded to C12 rather than the hydrogen here (H12).
The molecules are held in the lattice by a concerted set of C-H···π interactions shown in Table 1 Table 1 is included because the second methyl hydrogen on C1 (H1A) interacts with atoms C14 & C15 in an adjacent (Cg3) supplementary materials sup-2 ring. We note that the acidic proton H12 is not positioned to interact with adjacent N2 or N3 acceptors as observed in related compounds with cyano N atoms (e.g. structure (II) in Gainsford et al., 2008). This packing highlights the main difference between this structure and the reference compounds which have extensive hydrogen bonding (C-H···O) to the perchlorate anion and no significant C-H···π interactions.

Refinement
In the absence of significant anomalous scattering, the values of the Flack parameter were indeterminate. Accordingly, the Friedel-equivalent reflections were merged prior to the final refinements. Two reflections affected by the backstop were omitted from the refinements (using OMIT) and three others were deemed to be outliers. The methyl H atoms were constrained to an ideal geometry (C-H = 0.98 Å) with U iso (H) = 1.5U eq (C), but were allowed to rotate freely about the adjacent C-C bond. All other H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms with C-H distances of 1.00 (primary), 0.99 (methylene) or 0.95 (phenyl) Å with U iso (H) = 1.2U eq (C).    Table 1) [Macrae et al., 2008]. Only significant H atoms are shown as balls for clarity. Symmetry (i) x -1/2, 2 -y, z (ii) 1/2 -x, 1 -y, z (iii) x, y -1, z (iv) 1 -x, 1 -y, 1/2 + z (v) x -1/2, 1 -y, z. Ring centres shown as red balls are Cg1 (C19-C24), Cg2 (C4-C9) and Cg3 (C13-C18).