A PCT-based, pyrene-armed calix[4]crown fluoroionophore

A photoinduced charge transfer (PCT)-based 1,3-alternate calix[4]crown fluoroionophore containing two cation recognition sites, a crown ether ring and two facing pyreneamide groups, is synthesized. Upon addition of K⁺, Pb²⁺, or Cu²⁺, wavelength changes are observed in both the fluorescence and absorption spectra, but with different binding modes. With K⁺, fluorescence emissions of the ligand scarcely change, while addition of Pb²⁺ or Cu²⁺ produces a remarkable change in both the excimer and monomer emissions. The observed data indicate that the metal cation is encapsulated in the crown-5 ring for K⁺ and by the two facing amide groups in the latter case, which is verified by a metal ion exchange experiment. The wavelength shifts in both fluorescence and absorption spectra upon addition of Cu2+ show that, in contrast to Pb²⁺, Cu ²⁺ interacts with the nitrogen atoms of the amide groups, resulting in a PCT mechanism.