(BO)(2)‐Doped Tetrathia[7]helicene: A Configurationally Stable Blue Emitter

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 %).