Fluorenylidene bridged cyclotriphosphazenes: ‘turn-off’ fluorescence probe for Cu2+ and Fe3+ ions

Abstract

A first series of the 4,4′-(9-fluorenylidene)diphenol (FDP), (2) and 4,4′-(9-fluorenylidene)dianiline (FDA), (7) bridged cyclotriphosphazene derivatives (3–6, 8–11) were synthesized by nucleophilic S_N2(P) and S_N1(P) reactions, respectively. The structural investigations of the compounds were verified by elemental analyses, mass spectrometry, UV-vis, FT-IR, ¹H and ³¹P NMR techniques, X-ray crystallography (for 4, 8, 9) and fluorescence spectroscopy. The metal sensing properties of novel bridged cyclotriphosphazene derivatives were also examined by fluorescence spectroscopy. These complexes showed high selectivity for Cu²⁺ and Fe³⁺ ions in solution.