Novel Polyphenylenes Containing Phenol-Substituted Oxadiazole Moieties as Fluorescent Chemosensors for Fluoride Ion

Novel phenyl-based conjugated polymers with different content of 2,5-bis(2-hydroxyphenyl)-1,3,4-oxadiazole (1) or 2-(2-hydroxyphenyl)-5-phenyl-1,3,4-oxadiazole (2) units in the main chain were synthesized through Suzuki coupling. The measurements of sensing behavior to various anions, i.e., F^-, Cl^-, Br^-, I^-, BF₄^-, PF₆^-, and H₂PO₄^-, reveal that the polymers are highly sensitive and selective F^- sensory materials, and the sensitivity is much higher than that of small molecules 1 and 2. The best performance was observed with polymer P3 containing 40 mol % oxadiazole unit 1. A 380-fold fluorescence quenching occurred upon adding F^- into P3 chloroform solution, with only 6-fold reduction of emission by using H₂PO₄^- instead. Addition of other anions caused almost no change in emission spectra. The sensitivity of the polymers to F^- decreases with increasing solvent polarity. Like molecules 1 and 2, these polymers can also be used as colorimetric sensors for F^- and H₂PO₄^-.