Phenolphthalein based molecule as a lighting–up fluorescent chemoprobe for the nanomolar recognition of Al3+: DFT study and its applications in test kits, food and water samples

Abstract

Phenolphthalein–based compound (PHAB) was synthesized, well–characterized and studied as a lighting–up fluorescent chemosensor for Al3+. Fluorescence studies were performed at 25 °C in H2O/CH3CN (20/80, v/v) media. Free PHAB was non–fluorescent; but, it depicted a strong fluorescence toward Al3+ at 468 nm over potential competitive cations. The mechanism of C = N isomerisation and blocking PET enhanced its emission with a remarkable color alteration from colorless to blue. The LOD value was found at nano–molar level (51.5 nM), indicating high sensitivity toward Al3+. The validation study also confirmed the sensing performance of PHAB based on different analytical parameters. Job's plot, 1H NMR titration and MALDI TOF–MS studies authenticated the stoichiometry between PHAB and Al3+ (1:2). The binding of PHAB with Al3+ was further verified by the theoretical study. Furthermore, the fluorescence sensing performance of PHAB makes it perfect for practical applications in drinkable water and food samples with satisfactory recovery values (91.42%–108.8%), as well as in simple test–kit applications.