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

Abstract: Helicenes combine two central themes in chemistry: extended ?-conjugation and chirality. Heteroatom 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 kcalmol? 1 is lower than that of tetrathia[7]helicene (39.4?0.1 kcalmol? 1). The circular dichroism spectra of (P)- and (M)-1 show a perfect mirror-image relationship. 1 is a blue emitter (?em= 411 nm) with a photoluminescence quantum efficiency of ?PL=6% (cf. tetrathia[7]helicene: ?em?405 nm, ?PL= 5%).