A new turn-off fluorescent chemosensor for iron (III) based on new diphenylfluorenes with phosphonic acid

Novel phosphonic acid-functionalized fluorene derivatives 9, 9-bis (3′-phosphonic acid propyl)-2,7-diphenylfluorene and 2,7-diphenylfluorene-9-ylphosphonic acid, synthesized by Suzuki-Miyaura coupling reaction, were evaluated as a chemoselective Fe3+ ion sensor. Through the disappearance of the characteristic sorption peak of PO, POH and the form of new broad band (POFe stretching bands) in FT-IR spectra, it was verified that the Fe3+ ion cause the quenching of their fluorescence emission, due to the Fe3+ ion binding to them via the O-atoms of the phosphonic group. UV-vis analyses also gave evidences by the change of absorption peak of them. A linear relationship that flowed with the Perrin model of static quenching was observed between the relative fluorescence intensity (ln F0/F) of BPPDPF and the concentration of iron(III) in the range of 1-8 μM with a detection limit of 0.02 μM, so was with DPFPA in the range of 1-5 μM with a detection limit of 0.01 μM. Selectivity of them for Fe3+ was demonstrated over other metal ions by photoluminescence analysis in DMF-H2O solution. It showed that the other studied metal ions do not affect the determination of iron. We successfully monitored trace levels of iron (III) in tap water samples.