Binaphthyl–Bipyridyl Cyclic Dyads as a Chiroptical Switch

A series of chiral cyclic dyads, axially chiral binaphthyls linked to a 3,3'-bipyridyl, was synthesized. The dyad 2 bearing methoxy groups exhibited ON/OFF properties in circularly polarized luminescence (CPL), yielding a | glum| of 1.6 × 10⁻³ or 0 without any change in fluorescence. This type of CPL switch is unprecedented. Regioisomer 4 exhibited a dextro/ levo rotation switching ability in [α]D. X-ray structures as well as experimental and theoretical analyses suggested that the switching properties depended on conformational changes.