Bis[1]benzothieno[1,4]thiazines: Planarity, Enhanced Redox Activity and Luminescence by Thieno‐Expansion of Phenothiazine

Abstract Twofold Buchwald–Hartwig aminations selectively furnish three regioisomers of bis[1]benzothieno[1,4]thiazines; X‐ray structure analyses and DFT calculations were corroborated for correlation of their electronic properties. All regioisomers outscore the parent compound phenothiazine with respect to a low‐lying oxidation potential and reversible redox activity. The anti ‐ anti bis[1]benzothieno[3,2‐ b :2′,3′‐ e ][1,4]thiazines possess the lowest oxidation potentials in this series and displayed pronounced green luminescence in solution ( Φ F ≈20 %) and in the solid state. Syn ‐ anti regioisomers were only weakly luminescent in solution, but showed aggregation‐induced emission enhancement and solid‐state luminescence. Most interestingly, X‐ray structure analyses revealed that anti‐anti derivatives have an amazingly coplanar structure of the pentacyclic anellated 1,4‐thiazine system, emphasizing a structural similarity to heteroacenes. The calculated theoretical nucleus‐independent chemical shifts additionally suggested that these 8π‐electron core systems can be considered as the first electronically unbiased anellated 1,4‐thiazines with antiaromatic character.