The crystal structure of 2-[5-(dimethylamino)naphthalene-1-sulfonamido]phenyl 5-(dimethylamino)naphthalene-1-sulfonate

The complete molecule of the title compound, C30H29N3O5S2, is generated by a crystallographic twofold axis: the O atom and NH group attached to the central benzene ring are statistically disordered. The dihedral angle between the naphthalene ring system and the central benzene ring is 52.99 (6)°, while the pendant naphthalene ring systems subtend a dihedral angle of 68.17 (4)°. An intramolecular C—H⋯O hydrogen bond closes an S(6) ring. In the crystal, the molecules are linked by weak C—H⋯O hydrogen bonds.


S1. Introduction
Dansyl derivatives can be widely used as fluorescence probes in biological and environmental systems. Dansyl tags have been increasingly used to monitor biological activities in the enzyme system for providing the accurate information (Brown et al., 1970;Liu et al., 2010). An example is dansyl-conjugated liposome for modulating fluorescence resonance energy transfer (FRET) mechanism (Li et al. 2006). Furthermore, dansyl fluorogenic sensors were prepared for recognition and detection of many targets such as cationic and anionic species (Cao et al., 2014;Jisha et al., 2009;Bhalla et al., 2007). Crystal structures of dansyl derivatives (Bhatt et al., 2011;Zhang et al., 2009) and metal complexes of calix[4]arene bearing two dansyl carboxamide units have been reported (Buie et al., 2008).

S2. Synthesis and crystallization
The title compound was synthesized by condensation of 2-aminophenol (0.55 g, 5.04 mmol) and dansyl chloride (2.72 g, 10.08 mmol) using potassium carbonate (17.27 g, 12.50 mmol) as a base in acetonitrile (30 ml). The solution was heated and stirred under N 2 atmosphere for 24 h. The solvent was then removed by a rotary evaporator. Water (10 ml) was added to the residue and the organic phase was extracted with dichloromethane (3 x 20 ml). The organic layer was dried with Na 2 SO 4 . The product was purified by column chromatography using dichloromethane as an eluent. The solvent was evaporated to afford a yellow crystalline solid in 55% yield. Single crystals suitable for X-ray measurements were obtained by recrystallization using the mixture solution of dichloromethane and hexane (1:1, v/v) at room temperature.

S3. Refinement
Atom O1 and the N1H1 group attached to the central benzene ring are statistically disordered and were refined with the occupancies of the N, H and O atoms fixed at 0.5. All H atoms were positioned geometrically and refined using a riding model, with C-H = 0.93 Å for aryl and 0.96 Å for methyl H atoms, U iso (H) = 1.2U eq (C) for aryl and 1.5U eq (C) for methyl H atoms. The N-bound H-atom was refined with N-H = 0.86 Å, and with U iso (H) = 1.2U eq (N).

Figure 1
The molecular structure of the title compound with 30% probability ellipsoids and atom numbering. Hydrogen atoms are omitted for clarity.

Figure 2
The crystal packing of the title compound, viewed along the [110] direction.