Pyrene Scaffold as Real-Time Fluorescent Turn-on Chemosensor for Selective Detection of Trace-Level Al(III) and Its Aggregation-Induced Emission Enhancement

A pyrene based fluorescent probe, 3-methoxy-2-((pyren-2yl-imino)­methyl)­phenol (HL), was synthesized via simple one-pot reaction from inexpensive reagents. It exhibited high sensitivity and selectivity toward Al³⁺ over other relevant metal ions and also displayed novel aggregation-induced emission enhancement (AIEE) characteristics in its aggregate/solid state. When bound with Al³⁺ in 1:1 mode, a significant fluorescence enhancement with a turn-on ratio of over ∼200-fold was triggered via chelation-enhanced fluorescence through sensor complex (Al-L) formation, and amusingly excess addition of Al³⁺, dramatic enhancement of fluorescence intensity over manifold through aggregate formation was observed. The 1:1 stoichiometry of the sensor complex (Al-L) was calculated from Job’s plot based on UV–vis absorption titration. In addition, the binding site of sensor complex (Al-L) was well-established from the ¹H NMR titrations and also supported by the fluorescence reversibility by adding Al³⁺ and EDTA sequentially. Intriguingly, the AIEE properties of HL may improve its impact and studied in CH₃CN–H₂O mixtures at high water content. To gain insight into the AIEE mechanism of the HL, the size and growth process of particles in different volume percentage of water and acetonitrile mixture were studied using time-resolved photoluminescence, dynamic light scattering, optical microscope, and scanning electron microscope. The molecules of HL are aggregated into ordered one-dimensional rod-shaped microcrystals that show obvious optical waveguide effect