An AIE active anthracene-based Schiff base probe for “turn-on” detection of Cu²⁺ ions: Demonstrations with nanostructural investigations, DFT, cellular imaging, and real water analysis

An aggregation induced emission (AIE) active anthracene-based Schiff base probe “(2-((anthracen-9-ylmethylene) amino) phenol); AP” was synthesized via one-pot reaction and utilized in “turn-on” detection of Cu²⁺ ions. Ultraviolet–visible and photoluminescence (UV–vis/PL) interrogations confirm the AIE between 0 and 99 % water fraction (f_w) and high selectivity of AP to Cu²⁺. PL studies establish the linear regression of Cu²⁺ between 0 and 24 µM with a detection limit (LOD) of 53.2 nM. The Job plot and high-resolution mass (HR-mass) data affirm 2:1 stoichiometry and the association constant (K_a) value appraised as 1.88 × 10⁻⁴ M⁻². Time-resolved photoluminescence (TRPL) studies reveal decay kinetics of AIE, Cu²⁺ sensors and complex's reversibility. Moreover, ¹H NMR titration and density functional theory (DFT) investigations identify the binding mode, π-π stacking in AIE, AP − Cu²⁺ − AP* excimer formation, band gap variations and involvement of photoinduced electron transfer (PET) and chelation enhanced fluorescence (CHEF) mechanism. Crystallinity and nanostructural variations of AIE and Cu²⁺ sensors are investigated by using powder-X-ray diffraction (PXRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and dynamic light scattering (DLS). AIE and Cu²⁺ sensory method are validated by MDA-MB-231 cellular imaging studies. Finally, real water-based titrations show nanomolar LODs and recoveries > 97 % with RSDs < 3.5 %.