Dihydropyrimidones based chloride ion chemosensor functional in aqueous solution under environmentally relevant conditions

Compounds 1 and 2 were synthesised using multi-component one-pot condensation reaction between 2-hydroxynaphthaldehyde, urea/thiourea and ethyl/methyl acetoacetate, catalysed with Zn(ClO₄)₂·6H₂O in methanol. Compounds 1 and 2 were purified and characterised using ¹H and ¹³C NMR, mass and CHN analyses. Organic nanoparticles (ONPs) were developed from compounds 1 and 2 using reprecipitation technique. Size and morphology of nano-aggregates N1 and N2 were analysed using DLS and transmission electron microscope techniques. Nano-aggregates of 1 and 2 were further subjected to chemosensory applications in aqueous medium. Efficient nano-aggregates of compound 1 have shown excellent detection limit of 0.04 nM for chloride in aqueous medium. None of the other anions tested caused any interference in the detection of chloride. However, nano-aggregates of compound N2 were not active for any particular ion in aqueous medium. The difference in the recognition properties can be due to the difference in the size and electronegativity of oxygen and sulfur moieties attached on 1 and 2, respectively. The sensor was used to determine the chloride content in tap water. Results were validated using existing methods and the performance of the N1 was found to be in a satisfactory error range.