Fluorescent sensors for Ca2+ and Pb2+ based on binaphthyl derivatives

Two novel binaphthyl compounds have been synthesized for the selective fluorescent recognition of Ca2+ or Pb2+. By introducing different terminal groups to the receptor unit, the fluorescence signals of the receptors are significantly changed: 1 is fluorescence enhancement for Ca2+, 2 is fluorescence quenching for Pb2+. The binding properties for metal ions were examined by the absorption and fluorescence spectra. The fluorescence intensity enhancement was ascribed to the complex formation between Ca2+ and 1 which blocked the photo-induced electron transfer process.