Synthesis and X-ray analysis of a perfluoroalkyl-substituted azobenzene dye

• Single crystal X-ray structure of a perfluoroalkyl-substituted azobenzene dye.
• π-Electron densities differences between the ground and the electronically excited state.
• Synthesis and spectroscopic analysis of 4-N,N-diethylamino-4′-tridecafluorohexylazobenzene.

A search for colorants capable of reducing the surface energy of synthetic fibers as well as adding color led to the synthesis and characterization of the repellency behavior of dyes such as 4-N,N-diethylamino-4′-tridecafluorohexylazobenzene. Unexpectedly high surface energy values and a low fluorine content on fiber surfaces then led to an interest in determining the crystal structure of this new dye. Accordingly, a single crystal was grown from acetone solution, and its structure was established using X-ray diffraction analysis. Interestingly, it was found that the azobenzene skeleton is appreciably nonplanar, having an N2–N1–C1–C2 torsion angle of 30.6°, despite the absence of substituents ortho to the azo bond. Further, the structure is characterized by head-to-tail molecular stacking and the N-ethyl groups in the molecule are positioned above the aminobenzene plane on the same side. It is likely that this combination of factors contribute to the observed surface properties of the target dye.