Multiple-color aggregation-induced emission-based Schiff base sensors for ultrafast dual recognition of Hg ²⁺ and pH integrating Boolean logic operations

Seven Schiff base fluorescent sensors (L ¹ −L ⁷ ) with multiple-color aggregation-induced emission (AIE) properties for detection of Hg ²⁺ ions and pH integrating Boolean logic operations were reported. With appropriate ligand-to-metal coordination (L−HgCl ₂ ) and AIE characteristic, L−HgCl ₂ can aggregate into nanoparticles, followed by activation of strong emission, therefore, the “turn-on” assay for detection of Hg ²⁺ can be established. Sensing mechanism was calculated through single-crystal X-ray diffraction, Job’s Plot, Benesi−Hildebrand equation, dynamic light scattering, scanning electron microscopy, and elemental mapping analysis. Density functional theory calculations revealed that L−HgCl ₂ can avoid one-electron transfer and retain bright luminescence compared with that of L. Different (highest unoccupied orbit) HOMO and (Lowest empty orbit) LUMO energy gaps enable the different electron transitions, resulting in the multiple-color fluorescence properties. Especially, L ¹ −L ⁷ exhibit pH-dependent fluorescent characteristics: different electron-donating ability of the substituent groups for L ¹ −L ⁷ show different titration jump of pH. Advanced level molecular logic gates have been constructed integrating the sensing of Hg ²⁺ and pH. More importantly, the L-coated test paper applied in Hg ²⁺ sensing makes tracing possible, which is convenient for confidential purposes.