Selective detection of thorium (IV) in aqueous systems using advanced AIE materials : water-soluble AIE sensor for thorium detection

Thorium (Th), a naturally occurring radioactive element critical to India's strategic nuclear energy programs, also poses significant health risks due to its radiological and chemical toxicity. Accurate detection of Thorium in water is essential not only for environmental monitoring and health safety but also for ensuring its safe and sustainable utilization within the Department of Atomic Energy's initiatives. Traditional detection methods like ICP-MS require complex setups, while optical sensors offer cost-effective, simple, and selective solutions. However, achieving effective aggregation-induced emission (AIE)-based turn-on sensing for Th(IV) in 100% aqueous media has been a challenge due to the need for water-soluble, lowbackground fluorescence fluorophores. A novel fluorophore, tetra(4-sulfophenyl) ethylene (SuTPE), was developed, exhibiting significant emission enhancement upon aggregation induced by Th(IV) in pure water. This fluorophore demonstrated remarkable sensitivity with a limit of detection to 56 ppb and high selectivity, even in complex matrices such as tap and seawater. The underlying sensing mechanism was thoroughly validated using several techniques, including steady-state and time-resolved fluorescence, FTIR, SEM, AFM, and DLS. The aggregation of Th(IV) effectively restricts the intramolecular rotation in SuTPE, thereby blocking nonradiative decay pathways and significantly enhancing its fluorescence intensity