A new fluorescent probe for sensing Al3+ ions in the solution phase and CH3COO− in the solid state with aggregation induced emission (AIE) activity

Abstract

An AIE (aggregation induced emission) active probe DFP–AMQ was designed and synthesized as a hexa-coordinated N₂O donor chelator for the selective sensing of Al³⁺ colorimetrically as well as fluorimetrically with a 27-fold fluorescence enhancement for CH₃CN–H₂O (9 : 1, v/v, pH 7.2, HEPES buffer). The fluorescence enhancement occurred through the blocking of ESIPT, chelation enhanced fluorescence effect (CHEF) arose, and as a result fluorescence enhancement was observed through 1 : 1 complexation with Al³⁺ ions. Detailed spectroscopic studies including UV-Vis, FTIR, ¹H NMR, and HRMS studies were carried out to characterize the probable structure of DFP–AMQ including the complexation of DFP–AMQ with Al³⁺ ions. The spectrophotometric and spectrofluorimetric titrations revealed strong binding towards Al³⁺ and the K_d values were obtained from UV-Vis (3.26 × 10⁻⁵ M⁻¹) and fluorescence titration (2.02 × 10⁻⁵ M⁻¹). The limit of detection of Al³⁺ by DFP–AMQ was 1.11 μM. The quantum yields of DFP–AMQ and [DFP–AMQ–Al]⁺ were calculated to be 0.008 and 0.211, respectively. Dynamic light scattering (DLS) studies showed that the sizes of the particles increased with increasing water percentage due to aggregation. SEM (scanning electron microscopy) studies revealed interesting morphological changes in microstructures in which DFP–AMQ demonstrated a rod-like shape, which was converted to a spherical-like shape in the presence of Al³⁺ and when DFP–AMQ aggregated in H₂O it showed aggregated block-like shape. In the solid phase, DFP–AMQ with nitrate has no particular shape, but in the presence of acetate, it converts to stone-like shape. This probe (DFP–AMQ) could be employed for on-site Al³⁺ ion detection in the solid state.