Benzo[a][1,4]benzothiazino[3,2-c]phenothiazine

The title compound, C22H12N2S2, crystallizes in space group P21/c with four molecules in the asymmetric unit. The heterocyclic molecule is quasi-planar with a dihedral angle between the phenyl rings on the periphery of the molecule of 1.73 (19)°. Short H⋯S (2.92 Å) and C-H⋯π [2.836 (3) Å] contacts are observed in the crystal with shorted π-π stacking distances of 3.438 (3) Å along the b axis. Surprisingly, and unlike a closely related material, this molecule readily forms large crystals by sublimation and by slow evaporation from dichloromethane. The maximum absorbance in the UV-Vis spectrum is at 533 nm. Emission was measured upon excitation at 533 nm with a fluorescence λmax of 658 nm and cutoff of 900 nm.