Aggregation–induced emission activity and further Cu2+-induced self-assembly process of two Schiff compounds

Abstract Two Schiff-base compounds ( 1 and 2 ) based on the condensation of salicylaldehyde or 2-hydroxy-1-naphthaldehyde with hydrazine hydrate are designed and synthesized. The observation suggests that they are aggregation–induced emission (AIE) active compounds in pure aqueous solution with strong green emission, λ max  = 530 nm. Both of the aggregation, AIE ( 1) and AIE ( 2 ), show comparatively high sensitivity to Cu 2+ via emission significantly quenched compared to other metal ions of interest. Notablely, 3-folds reduction of the fluorescence intensity is observed when 0.2 equiv. of Cu 2+ ions is added to AIE ( 2 ) (10 μM) in aqueous solution. Detection limit for Cu 2+ is (200 ± 23) nM ( 1 ) and (10 ± 0.3) nM ( 2 ), respectively. Importantly, mechanism investigation by dynamic light scattering (DLS), scanning electron microscopy (SEM), ESI–MS, 1 H NMR, resonance light scattering spectra and EDTA competing analysis indicate that the presence of Cu 2+ induced the rearrangement of AIE ( 1 ) or AIE ( 2 ) with the formation of a very tight self-assembly [ 1 -Cu 2+ ] n or [2 -Cu 2+ ] m particle. The AIE effect and Cu 2+ -induced self-assembly subsequently have been achieved in bioimaging with satisfactory results.