A stilbene-based fluoroionophore for copper ion sensing in both reduced and oxidized environments

The high sensitivity and abundance of fluorophores makes fluorescence technique among one of the most promising tools to develop chemo- and biosensors. Fluorescent sensors for ions, also called fluoroionophores, are commonly composed of an ion recognition unit (ionophore) and a fluorogenic unit (fluorophore). Here we report the synthesis and characterization of a new stilbene derivative conjugated with the di-2-picolylamine (dpa) group. It is found that the fluorescence of the stilbene derivative using dpa as ionophore is sensitive to copper ions, including Cu²⁺ (oxidized state) and Cu⁺ (reduced state). The sensitive and selective stilbene-based fluoroionophore for copper ions are based on the internal charge transfer along with the electron donor-π-acceptor stilbene motif and incorporate a dpa-containing aniline-derivatized ligand framework. By modifying the stilbene with di-2-picolylamine (dpa), the significant fluorescence quenching was observed upon binding with copper ions involving both the reduced and oxidized environments, indicating the great sensitivity and specificity for copper ion sensing. The presence of metal ions such as Ag⁺, Al³⁺, Ba²⁺, Ca²⁺, Cd²⁺, Co²⁺, Cr³⁺, Fe²⁺, Fe³⁺, Hg²⁺, K⁺, Mg²⁺, Mn²⁺, Na⁺, Ni²⁺, Pb²⁺, Sn²⁺, and Zn²⁺ had little influence on the selectivity and sensitivity of Cu²⁺ and Cu⁺. The optical sensor design undertakes promising for potential application to multiplex sensing of different analytes through distinct ligand conjugation and functionalization of individual fluorophore.