Ion-Induced Supramolecular Reorganization of Cationic Oligo-Polyvinylene Derivatives for Bromide–Iodide Discrimination in Aqueous Medium

Abstract

Among halides, iodide is an essential micronutrient required in body for thyroid hormone synthesis and neurodevelopment, both deficiency and excess intake can lead to serious health issues, including goiter and hypothyroidism. In contrast, bromide, widely encountered through fumigants, processed foods, and natural water sources, poses toxicological risks at elevated levels, including neurotoxicity, endocrine disruption, and reproductive effects. Thus, selective detection as well as discrimination of halide ions in aqueous environments is a critical challenge in environmental and food safety monitoring. Herein, we report a rationally designed series of π-conjugated stilbene derivatives (compounds 1, 2, and 3), featuring pyridine or pyridinium termini with tunable self-assembly and charge-transfer properties. Compounds 1 and 2, synthesized via N-alkylation and aldol-type condensation, respectively, form distinct self-assembled aggregates in water, enabling differential optical responses toward halide ions. Fluorescence studies in aqueous medium revealed selective and sensitive detection of iodide via heavy atom-induced static quenching (~80 fold), while bromide induced a supramolecular reorganisation in compound 2, shifting emission from 470 to 620 nm. This dual-channel fluorescence allowed us to unambiguously distinguish I⁻ from Br⁻, a rarely reported capability in aqueous systems. All experiments were conducted using environmentally relevant analyte concentrations (0-0.2 mM), and the platform showed excellent reproducibility, low detection limits (~0.2-0.3 µM), and rapid response times (< 2 min). Real-life validation using iodized salt, grains, soil, seaweed, and mineral water confirmed the sensor’s performance without extensive sample pretreatment, and a paper-based platform was further developed for field-deployable applications. Compared to conventional techniques such as HPLC and GC-MS, this fluorescence-based strategy offers a portable, cost-effective, and practical solution for halide ion monitoring in food, water, and environmental matrices.