A novel colorimetric and fluorometric method based on coumarin as signalling unit was developed for Hg2+ recognition and quantification. Initially, the alkyne functionality was incorporated into a coumarin system and the resulting molecule showed higher specificity and sensitivity for Hg2+ over other cations in both absorption and emission sensing assays. The Hg2+ recognition was detected as visible colour change from colourless to yellow and as fluorescence quenching. The colour change was assigned to the increased intramolecular charge transfer (ICT) in the signalling unit upon Hg2+ binding whereas a decline in the fluorescence intensity was ascribed to the heavy atom effect from Hg2+. In order to generate a material with high sensing performance level, alkyne-functionalized molecule was hosted into a polymeric material. The resulting functionalized polymer showed higher sensitivity and selectivity for Hg2+ over its corresponding coumarin molecule. The investigation of the possible binding modes for Hg2+ suggested both alkyne and triazole functionalities as potential binding sites for Hg2+. The limit of detection (LOD) and limit of quantification (LOQ) of the proposed method were evaluated and values less than a recommended maximum level of Hg2+contaminant in drinking water (2.00 μg/L) were obtained (LOD = 0.44 μg/L and LOQ = 1.33μg/L). The real-life application of the method was investigated using natural water samples containing Hg2+ levels equivalent to the maximum tolerable concentration of Hg2+ in drinking water. The outcomes suggested that the method could be used in the sensing and determination of Hg2+ level of contaminant in the environment.
Keywords: Fluorescence quenching; Functional linkage; ICT; Post-polymerization functionalization; Recognition events.