Synthesis of yellow-emitting fluorescent aniline-doped ellagic acid via C-N coupling reaction and its application in the selective detection of metal ions

Ellagic acid (EA), a natural polyphenol, features a highly organized planar structure with an extensive sp 2 carbon-conjugated area, making it favorable for light energy absorption and fluorescent emission. However, this planar structure can easily aggregate through π-π stacking, leading to aggregation-caused quenching of fluorescence. In this research, aniline-doped ellagic acid (EAAn 2 ) was successfully synthesized via a C-N coupling reaction to address this issue. The fluorescence properties of EAAn 2 in various organic solvents were thoroughly investigated. Compared to EA, EAAn 2 exhibited a red shift in fluorescence emission, primarily revealing yellow fluorescence instead of the green fluorescence of EA. Moreover, the fluorescence intensity and the concentration at which aggregation-caused quenching occurs for EAAn 2 were substantially improved due to the two grafted aniline molecules. EAAn 2 was utilized as a molecular fluorescent probe in DMSO to detect three kinds of metal ions: alkali and alkaline-earth metal ions, transition metal ions, and post-transition metal ions, using EA as a control. It was found that the combination of EAAn 2 with these metal ions exhibited stronger fluorescence intensity than EA and effectively resisted the blue shift in fluorescence emission due to aniline doping. Based on these results, Mg 2 ⁺ ions could be clearly distinguished from other alkali and alkaline-earth metal ions by differences in their fluorescence emission, as could Cr 2 ⁺ ions among transition metals. This research effectively enhances the fluorescence properties of EA through C-N coupling and demonstrates its greater potential in the detection of metal ions, providing fundamental and valuable information for future fluorescent applications.