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.