H-aggregation induced dual emissive carbon nanoparticles for ratiometric detection of uranyl ions through dynamic to static excimer formation

Abstract

In this study, the photophysical mechanism of ratiometric detection of the uranyl ion (UO₂²⁺), a critical aspect of environmental monitoring and nuclear waste management, has been elucidated. For this purpose, H-aggregation-induced dual emissive furfural moieties in carbon nanoparticles (CNPs) were synthesized using dextrose through hydrothermal treatment. Detailed steady-state and time-resolved spectroscopic analysis revealed that the dynamic excimer exhibited by CNPs transforms into a static excimer upon the addition of UO₂²⁺, which is responsible for ratiometric sensing and results in concurrent quenching of blue and enhancement of excimer-induced green emission. The static excimer is believed to be formed by coordinating the dispersed molecular fluorophore with UO₂²⁺, which is facilitated through LMCT transition from the HOMO of the equatorially bonded fluorophore to the low-lying LUMO of uranium(VI), causing the quenching of the blue emission. A modified SV plot for the fluorescence quenching of CNPs in the detection of UO₂²⁺ was observed in the concentration range of 25–200 μM, and the limit of detection (LOD) was calculated to be as sensitive as 12 nanomolar.