Bis[1]benzothieno[1,4]thiazine‐ <i>S</i> ‐oxides–Luminescence of the <i>Anti</i> ‐ <i>Anti</i> ‐Regioisomer

Abstract Three regioisomeric N ‐ para ‐fluorophenyl bis[1]benzothieno[1,4]thiazines (BBTT) are selectively oxidized under mild conditions to give the corresponding BBTT‐ S ‐oxides, which were fully characterized by single crystal structural analysis. The newly formed S ‐oxide is uniformly oriented in a pseudo‐axial S ‐ extra position, whilst the N ‐aryl substituent adopts an N ‐ intra conformation. In comparison to the diminished planarization of the BBTT scaffold according to DFT calculations, the structures are considerably planarized in the crystal. Only the anti ‐ anti ‐BBTT‐ S ‐oxide emits intensively and the electronic structure of the absorption and emission spectra can be elucidated by TDDFT calculations. This blue emission, both in solution (Φ f = 17%) and in the solid state (Φ f = 66%), is significant and qualifies this isomer as an attractive emitter.