Novel pyrene- and anthracene-based Schiff base derivatives as Cu2+ and Fe3+ fluorescence turn-on sensors and for aggregation induced emissions

Abstract

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 Fe³⁺ 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 + Fe³⁺) 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 CH₃CN 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.