Fluorescent organic nanoparticles based on branched small molecule: preparation and ion detection in lithium-ion battery.

Fluorescent organic nanoparticles (FONs) as a new class of nanomaterials can provide more advantages than molecule based probes. However, their applications in specific metal ion detection have rarely been exploited. We design and synthesize a branched small-molecule compound with triazole as a core and benzothiadiazole derivative as branches. By a facile reprecipitation method, nanoparticles (NPs) of this compound can be prepared in aqueous solutions, which can show high selectivity and sensitivity to Fe(III) ions based on fluorescence quenching. In addition, the fluorescence intensity of these NPs is resistant to pH changes in solutions. Such characters of this kind of NPs can be utilized in Fe(3+) impurity detection in a promising cathode material (LiFePO4) for lithium ion batteries. When exposed to Fe(3+), both the triazole and benzothiadiazole groups contribute to the fluorescence quenching of NPs, but the former one plays a more important role in Fe(3+) impurity detection. The sensing mechanism has also been investigated which indicates that a Fe-organic complex formation may be responsible for such sensing behavior. Our findings demonstrate that specific metal ion detection can be realized by FONs and have extended the application field of FONs for chemical sensing in aqueous solutions.