Reversible pH-Responsive Fluorescence of Water-Soluble Polyfluorenes and Their Application in Metal Ion Detection

摘要

A novel water-soluble conjugated polymer poly{(4,4'-azobenzene)-2,7-[9,9-bis(6'-N',.N,N,-trimethylammonium)hexyl fluorene] dibromide} (PFAB) has been designed and synthesized via Suzuki cross-coupling the fluorene units and azobenzene units. Through simple photo-reduction, the azo group of the nonfluorescent PFAB to hydrazine group using UV light, polyfluorene PFAB-L with turn-on fluorescence in aqueous solution is obtained. The optical measurements illustrate that the generation of the flexible hydrazine group induces face-to-face arrangement of phenyl—fluorene—phenyl moieties. Therefore, the excimer formation of phenyl—fluorene—phenyl moieties was induced in PFAB-L. And the fluorescence of PFAB-L can be controlled through modulating the protonation of the — NH—NH— group in solution with different pH. The pH-responsive property is reversible. Moreover, the Fe~(3+) ions can selectively quench the fluorescence of the PFAB-L. This new polymer PFAB-L could be used for selective and sensitive sensing Fe~(3+) ions in aqueous solution.