Novel pyrene- and anthracene-based Schiff base derivatives as Cu ²⁺ and Fe³⁺ fluorescence turn-on sensors and for aggregation induced emissions

Novel pyrene- and anthracene-based Schiff base derivatives P1 and A1 were synthesized via a one-pot reaction and utilized as fluorescence turn-on sensors towards Cu²⁺ and Fe³⁺ ions, respectively, and for aggregation induced emissions (AIEs). P1 in CH₃CN and A1 in THF illustrated the fluorescence turn-on sensing towards Cu²⁺ and Fe ³⁺ ions, respectively, via chelation enhanced fluorescence (CHEF) through excimer (P1-P1* and A1-A1*) formation. The 2:1 stoichiometry of the sensor complexes (P1 + Cu²⁺ and A1 + Fe³⁺) were calculated from Job plots based on UV-Vis absorption titrations. In addition, the binding sites of sensor complexes (P1 + Cu²⁺ and A1 + Fe ³⁺) were well established from the ¹H NMR titrations and supported by the fluorescence reversibility by adding metal ions and PMDTA sequentially. The detection limits (LODs) and the association constant (K _a) values of P1 + Cu²⁺ and A1 + Fe³⁺ sensor responses were calculated by standard deviations, linear fittings and from their fluorescence binding isotherms. More importantly, P1 + Cu²⁺ and A1 + Fe³⁺ sensors were found to be active in wide ranges of pHs (1-14 and 2-14, respectively). Moreover, the time effect along with the enhancements of quantum yield (Φ) and time resolved photoluminescence (TRPL) decay constant (τ) towards sensor responses were investigated. Similarly, P1 in CH ₃CN and A1 in THF showed AIEs by increasing the aqueous media concentration from 0% to 90%, with altered fluorescence peak shifts (red and blue shifts, respectively). As well as τ value enhancements, the Φ values of 0.506 and 0.567 (with 630- and 101-fold enhancements) were acquired for P1 in CH₃CN:H₂O (20:80) and A1 in THF:H₂O (40:60), respectively.