A synthetic approach to two regioisomeric πelectron extended [1,4]thiaborins annulated with two benzothiophene units has been developed. The central thiaborin rings of the boracycles obtained exhibit different electronic properties; this is reflected in their different aromatic characters, boron Lewis acidity and UV-vis spectroscopic behavior. Thiaborins were converted to boron dipyrromethene (BODIPY) complexes. Their emission spectra exhibit two distinct bands resulting from 1 LE and 1 CT transitions. Strong near-infrared phosphorescence in Zeonex thin films at 77 K indicates efficient intersystem crossing and the formation of triplet states. Separation of HOMO and LUMO orbitals between boracyclic and BODIPY moieties facilitates electron transfer to a 1 CT state followed by a transition to the 3 LE triplet state located on the ligand. These unique properties of spiro thiaborin-BODIPY complexes were explored for their application as singlet-oxygen photosensitizers. They show excellent photocatalytic performance with singlet oxygen quantum yields reaching 77 % and full conversion of the model organic substrate achieved after 1.5 h with only 0.05 % mol catalyst load.

Invited for the cover of this issue are Krzysztof Durka and co‐workers at Warsaw University of Technology, University of Warsaw, Silesian University of Technology and Heinrich‐Heine‐Universität. The image depicts the generation of singlet oxygen by the BODIPY photosensitizer. Read the full text of the article at 10.1002/chem.202300680.

Singlet oxygen is generated by the BODIPY photosensitizer, whose X‐ray structure is shown in the central part of the picture. The structures in the left and right corners of the doors are those of bis(benzothienylo)[1,4]thiaborins—basic building blocks of BODIPY. The sensitization process requires white light, which is symbolized by a light bulb. Triplet oxygen enters through the red door, where it is excited to the singlet state, and leaves through the blue door. More information can be found in the Research Article by P. H. Marek‐Urban, K. Durka, and co‐workers (DOI: 10.1002/chem.202300680). Artwork by P.H.M.‐U.