(BO)<sub>2</sub>‐Doped Tetrathia[7]helicene: A Configurationally Stable Blue Emitter
Luigi Menduti, Clara Baldoli, Simone Manetto, Michael Bolte, Hans-Wolfram Lerner, Giovanna Longhi, Claudio Villani, Emanuela Licandro, Matthias Wagner
Abstract
Abstract Helicenes combine two central themes in chemistry: extended π‐conjugation and chirality. Hetero‐atom doping preserves both characteristics and allows modulation of the electronic structure of a helicene. Herein, we report the (BO) 2 ‐doped tetrathia[7]helicene 1 , which was prepared from 2‐methoxy‐3,3′‐bithiophene in four steps. 1 is formally derived by substituting two (Mes)B−O moieties in place of (H)C=C(H) fragments in two benzene rings of the parent tetrathia[7]helicene. X‐ray crystallography revealed a dihedral angle of 50.26(9)° between the two terminal thiophene rings. The ( P )‐/( M )‐ 1 enantiomers were separated by chiral HPLC and are configurationally stable at room temperature. The experimentally determined enantiomerization barrier of 27.4±0.1 kcal mol −1 is lower than that of tetrathia[7]helicene (39.4±0.1 kcal mol −1 ). The circular dichroism spectra of ( P )‐ and ( M )‐ 1 show a perfect mirror‐image relationship. 1 is a blue emitter ( λ em =411 nm) with a photoluminescence quantum efficiency of Φ PL =6 % ( cf . tetrathia[7]helicene: λ em ≈405 nm, Φ PL =5 %).