Fluorenylidene bridged cyclotriphosphazenes: 'turnoff' fluorescence probe for Cu2+ and Fe3+ ions

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(N)2(P) and S(N)1(P) reactions, respectively. The structural investigations of the compounds were verified by elemental analyses, mass spectrometry, UV-vis, FT-IR, H-1 and P-31 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.