Wavelength-tunable AIEgens based on 6-methoxy-2-naphthaldehyde: AIE behavior and bioimaging performance

AIE-active dyes have lately received considerable attention due to their versatile applications, especially in bioimaging and theranostics. Herein, 6-methoxy-2-naphthaldehyde was used to construct fluorophores through Knoevenagel condensation with various active methylene compounds. All the obtained compounds showed varying degrees of AIE characteristics. It was worth mentioning that the condensation product of 6-methoxy-2-naphthaldehyde and malononitrile (MOP-e) exhibited a large redshift and a large Stokes shift when forming aggregates. Furthermore, it showed an ultra-wide AIE band which enabled it to be utilized for dual-channel bioimaging. The single crystal X-ray diffraction analysis showed that two different molecular arrangement modes, the monomolecular stacking and the discrete π-π dimeric stacking, existed in the aggregates of MOP-e. The discrete dimeric stacking leads to excimer-induced enhanced emission, which results in its unique AIE behavior. Moreover, MOP-e displayed an excellent bioimaging performance in living cells in green channel and in red channel respectively.