4-{(E)-2-[4-(But-3-en-1-yloxy)phenyl]diazen-1-yl}benzoic acid

The title compound, C17H16N2O3, has an E conformation about the azobenzene (–N=N–) linkage. The benzene rings are twisted slightly with respect to each other [6.79 (9)°], while the dihedral angle between the plane through the carboxy group and the attached benzene ring is 3.2 (2)°. In the crystal, molecules are oriented with the carboxy groups head-to-head, forming O—H⋯O hydrogen-bonded inversion dimers. These dimers are connected by C—H⋯O hydrogen-bonds into layers lying parallel to the (013) plane.


Related literature
199 parameters H-atom parameters constrained Á max = 0.51 e Å À3 Á min = À0.33 e Å À3 Table 1 Hydrogen-bond geometry (Å , ). latter can also occur in the "dark" by a process known as "thermal back relaxation" in a period ranging from minutes to tens of hours depending on the system. In this case molecules again transform from the metastable cis-conformation to the energetically stable trans-conformation. In conclusion, the present investigation on rod-shaped azo dyes is very useful for a variety of photonic applications. Excellent quality, cost effective, easy to prepare, are properties which make these devices very attractive for future generations. Detailed investigations on the physics of these azo dyes is under intense consideration.
In the crystal, the carboxyl groups are oriented head-to-head forming hydrogen bonded inversion dimers (Table 1 and Fig. 2). These dimers are further linked by C-H···O hydrogen bonds to a generate a layer parallel to the (013) plane (Table 1 and Fig. 2).

Experimental
The title compound was prepared from ethyl 4-aminobenzoate. Firstly the diazonuim salt was prepared using one equivalent of sodium nitrite to one equivalent of ethyl 4-aminobenzoate in methanol -water mixture at 275 K, in the presence of 3 equivalents of aqueous hydrochloric acid, which was coupled with phenol to yield ethyl 4-[(4-hydroxyphenyl)diazenyl]benzoate. This compound was then alkylated with 4-bromo-1-butene in the presence of potassium

Refinement
The H atoms were all located in a difference Fourier map, but those attached to carbon atoms were repositioned geometrically. They were all initially refined with soft restraints on the bond lengths and angles to regularize their geometry: C-H = 0.93 (2)-0.98 (2) Å and O-H = 0.82 (2) Å with U iso (H) = k × U eq (O,C) where k = 1.5 for the OH H atom and = 1.2 for the C-bound H atoms. In the final cycles or refinement they were allowed to ride on their parent atom.

Figure 1
The molecular structure of the title molecule with the atom numbering and displacement ellipsoids drawn at the 50% probability level.

Special details
Refinement. This compound, 9940 numbers of reflections were collected and measured during the refinement. Symmetry related reflections were measured more than once and after merging the symmetry equivalent reflections there were only 2783 reflection left. 10 more reflections were filtered, as sigma cutoff was set as 3 and (sinθ/x)set to>0.01 (to eliminate reflection measured near the vicinity of beam stop) therefore numbers of reflection reduced to 2773.