Polarization effect in luminescent mesogenic BF2 complexes derived from heterocyclic benzothiazoles

Abstract Two series of benzo(thia)xazoles 1–2 and one series of boron difluoride complexes 2-BF2 derived from benzothiazoles 2 were reported, and their mesomorphic and optical properties were investigated. The crystal and molecular structures of compound 2 and 2-BF2 (all n = 8) were determined by means of X-ray structural analysis, and both crystallize in the triclinic P-1 and monoclinic P21/c. The geometry at boron center is perfectly tetrahedral, and the overall molecular shapes are considered as rod-shape. Both benzo(thia)xazoles 1 and 2 exhibited N or/and SmC phase, and boron complexes 2-BF2 formed N or/and SmC phase. Benzothiazoles 2 showed a much wider temperature range of mesophase than those of benzoxazoles 1, which were attributed to the better polarization by sulfur atom incorporated. Boron complexes 2-BF2 (n = 10, 12) emitted a yellow-to-green emission at λmax = 569–571 nm in CH2Cl2. This is the first mesogenic BF2 complexes derived from benzothiazoles.