Exploring the Scope of Photo-Induced Electron Transfer–Chelation-Enhanced Fluorescence–Fluorescence Resonance Energy Transfer Processes for Recognition and Discrimination of Zn(2+), Cd(2+), Hg(2+), and Al(3+) in a Ratiometric Manner: Application to Sea Fish Analysis

[Image: see text] A rhodamine-based smart probe (RHES) has been developed for trace-level detection and discrimination of multiple cations, viz. Al(3+), Zn(2+), Cd(2+), and Hg(2+) in a ratiometric manner involving photo-induced electron transfer–chelation-enhanced fluorescence–fluorescence resonance energy transfer processes. The method being very fast and highly selective allows their bare eye visualization at a physiological pH. The optimized geometry and spectral properties of RHES and its cation adducts have been analyzed by time-dependent density functional theory calculations. RHES detects as low as 1.5 × 10(–9) M Al(3+), 1.2 × 10(–9) M Zn(2+), 6.7 × 10(–9) M Cd(2+), and 1.7 × 10(–10) M Hg(2+), whereas the respective association constants are 1.33 × 10(5) M(–1), 2.11 × 10(4) M(–1), 1.35 × 10(5) M(–1), and 4.09 × 10(5) M(–1). The other common ions do not interfere. The probe is useful for intracellular imaging of Zn(2+), Cd(2+), and Hg(2+) in squamous epithelial cells. RHES is useful for the determination of the ions in sea fish and real samples.