The multichannel fluorescence emission of europium(III) complex based on dehydroabietic acid derivative for detection of haloacetic acids

Three Eu(III) complexes, named DDA-Eu-7, DDI-Eu-7, and DDE-Eu-7, are constructed by dehydroabietyl imidazoline, ethyl aminoimidazole dehydroabietyl imidazoline, and ethyl esterimidazole dehydroabietyl imidazoline units, respectively. The coordinate structures of three Eu(III) complexes are characterized by FTIR, UV-vis, TG/DTG, ESI-MS, WAXD, elemental analysis, and XPS measurements. Among three Eu(III) complexes, DDA-Eu-7 exhibits the highest fluorescence lifetime (537.46 μM), the largest absolute quantum yield (54.84%), and the narrowest FWHM of ⁵D₀→⁷F₂ transition (5.9 nm). Due to the coordinate structure with high electric diploe and ligand polarization induced by more imidazole groups, DDA-Eu-7 exhibits more Stark-splitting emission peaks than those of DDI-Eu-7 and DDE-Eu-7. The results of fluorescence emission and the Judd–Ofelt parameters indicate that DDA-Eu-7 demonstrates the highest asymmetry of the coordinate structure. The fluorescence quenching ability of haloacetic acids on DDA-Eu-7 is in the order of iodoacetic acid > bromoacetic acid > chloroacetic acid. The analysis of fluorescence spectra and fluorescence lifetime verify that the quenching process of DDA-Eu-7 induced by iodoacetic acid conforms to the dynamic quenching model with the limit of detection of 2.31 μM, whereas the quenching processes invoked by chloroacetic acid and bromoacetic acid are in accord with the mixed quenching model including static and quenching models.