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

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 (ALE) active compounds in pure aqueous solution with strong green emission, lambda(max) =530 nm. Both of the aggregation, AIE (I) and AIE (2), show comparatively high sensitivity to Cu2+ 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 Cu2+ ions is added to AIE (2) (10 mu M) in aqueous solution. Detection limit for Cu2+ 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, H-1 NMR, resonance light scattering spectra and EDTA competing analysis indicate that the presence of Cu2+ induced the rearrangement of AIE (1) or AIE (2) with the formation of a very tight self-assembly [1-Cu2+](n) or [2-Cu2+](m) particle. The AIE effect and Cu2+-induced self-assembly subsequently have been achieved in bioimaging with satisfactory results. (C) 2017 Elsevier B.V. All rights reserved.