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.