Quinoline- and isoquinoline-derived ligand design on TQEN (N,N,N′,N′-tetrakis(2-quinolylmethyl)ethylenediamine) platform for fluorescent sensing of specific metal ions and phosphate species

Abstract

Rational molecular structure alterations of TQEN (N,N,N′,N′-tetrakis(2-quinolylmethyl)ethylenediamine) produced variable fluorescent sensors for specific metal ions and phosphate species. Utilization of methoxy-substituted quinoline and isoquinoline chromophores, conformational restriction and multidentate coordination structure allow discrimination between Zn²⁺ and Cd²⁺. Pyrophosphate (P₂O₇⁴⁻, PPi) and phosphate (PO₄³⁻) also are selectively detected with dinuclear Zn²⁺ complexes of tetrakisquinoline-based ligands. Differential stability and structure of the metal complexes, as well as resulting fluorescence enhancement mechanism, such as intramolecular excimer formation via change in coordination geometry, play key roles in the discrimination of target ions.