Substituent dependent sensing behavior of Schiff base chemosensors in detecting Zn2+and Al3+ ions: Drug sample analysis and living cell imaging

Abstract

Some novel Schiff base chemosensors (L1-L5) have been designed on the basis of electron activating/ deactivating properties in the salicyldehyde ring and developed to detect Al3+ and Zn2+ selectively in MeOH-H2O (1/9; v/v) solvent system. The chemosensor, L1 has been characterized by single crystal X-ray crystallography apart from various common spectroscopic techniques and ESI-MS. Among those, the molecular probe having most electronegative group selectively sense Al3+ and Zn2+ by switching on the fluorescence in the adduct. The molecule L1 remains non-fluorescent in solution due to photo-induced electron transfer (PET), excited state intramolecular proton transfer (ESIPT) and C[dbnd]N bond isomerization. However, in presence of metal ion, chelation-induced enhanced fluorescence (CHEF) comes into play to inhibit all the processes and induce dramatic fluorescence increase in the adduct. The underlying mechanism and experimental observations have been corroborated with theoretical calculations. The chemosensor, L1 has been found to be effective to determine the concentration of the selective ions in real sample (drug analysis) and detect them in living cells through optical imaging at physiological pH. The LOD value for Al3+ and Zn2+ have been found to be 8.04 × 10−7 and 7.95 × 10−7 M range respectively. The sensor-metal ion adduct can be further distinguished selectively by turning off the fluorescence of the adduct upon treatment with specific anions for particular metal ion. © 2018 Elsevier B.V.