Highly Luminescent, Electron-Deficient Bora-cyclophanes

A highly luminescent conjugated organoboron macrocycle containing six Lewis acidic boron centers was synthesized. Comparison of the optical and electronic properties with those of a hexameric linear oligomer revealed important differences due to delocalization within the highly symmetric cyclic conjugated structure. Exposure of this unique electron-deficient bora-cyclophane to fluoride or cyanide results in amplified fluorescence quenching and can be exploited to switch between an electron-deficient macrocycle and a highly charged, electron-rich borate cycle.