Crystal structure of (E)-2-cyano-3-(12-methyl-12H-benzo[b]phenothiazin-11-yl)acrylic acid

In the title compound, C21H14N2O2S, a donor–acceptor type of benzo[b]phenothiazine (bpz) derivative, the thiazine ring adopts a boat conformation and the bond-angle sum at the N atom is 360.0°. The dihedral angle between the benzene ring and the naphthelene ring system fused to the thiazine ring is 32.76 (5)°. In the crystal, carboxylic-acid inversion dimers linked by pairs of O—H⋯O hydrogen bonds generate R 2 2(8) loops. Aromatic π–π stacking [shortest centroid–centroid separaton = 3.5242 (13)Å] consolidates the structure and very weak C—H⋯O and C—H⋯N interactions also occur.

In the title compound, C 21 H 14 N 2 O 2 S, a donor-acceptor type of benzo [b]phenothiazine (bpz) derivative, the thiazine ring adopts a boat conformation and the bond-angle sum at the N atom is 360.0 . The dihedral angle between the benzene ring and the naphthelene ring system fused to the thiazine ring is 32.76 (5) . In the crystal, carboxylic-acid inversion dimers linked by pairs of O-HÁ Á ÁO hydrogen bonds generate R 2 2 (8) loops. Aromaticstacking [shortest centroid-centroid separaton = 3.5242 (13)Å ] consolidates the structure and very weak C-HÁ Á ÁO and C-HÁ Á ÁN interactions also occur.
As part of our studies for understanding the donor-acceptor interaction type dye molecule for dye-sensitized solar cell (Watanabe et al., 2014), we now report the title compound. In the title compound, C 21 H 14 N 2 O 2 S, consists a 12- phenothiazine as a donor moiety, which has a (E)-2-cyanobut-2-enoic acid moiety as acceptor at Dark-red crystals were obtained from 0.013 g of title compound in tetrahydrofuran (10 ml) solution by slow diffusion.
The C 21 H 14 N 2 O 2 S of 12-methyl-12H-benzo[b]phenothiazine moiety takes pyramidal structure, in which benzene and naphthalene had 147.2°, while the olefin bond at the cyanoacrylic moiety existed 123.8° from the naphthalene plane ( Figure 1). The title compounds showed an intermolecular hydrogen bonding at O1-H14 -O2′ (1.520 Å) in the two molecule structure of carboxylic acid moiety ( Figure 2). Furthermore, title compound have π-π stacking orientation along with a axis, where the two-naphthalene moieties oriented the parallel structures, which has a transannular distance at 3.273 Å ( Figure 3).

S2. Crystallization
The chloroform solution (10 ml) of title compound (0.013 g) was standing under ambient condition until the desired single crystal was produced.

S3. Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1 The molecular structure of C 21 H 14 N 2 O 2 S with displacement ellipsoids drawn at the 50% probability level.