Circularly Polarized Luminescence Liquids Based on Siloxybinaphthyls: Best Binaphthyl Dihedral Angle in the Excited State.

A series of axially chiral 1,1'-binaphthyls with trialkylsiloxy (OSiR 3 ) groups were synthesized. Among them, 1a - c possessing OSiR 3 groups at the 7,7'-positions and methyl groups at the 2,2'-positions were liquids at room temperature, and the neat liquids showed circularly polarized luminescence (CPL) (R = Bu; Φ fl,liquid = 0.21, | g lum,liquid | = 1.6 × 10 -3 ). The | g lum,liquid | value is the highest of pure liquids. These compounds remained liquid over a broad range of temperature, down to -50 °C. TD DFT calculations indicated that in the excited state, the binaphthyls adopt a transoid conformation with a small angle between the electric and magnetic transition dipole moments ( θ μ , m = 77°), which is a key factor in their CPL-activity. The best binaphthyl dihedral angle in the excited state is approximately 110°.