Red-emitting salicylaldehyde Schiff base with AIE behaviour and large Stokes shift

Three salicylaldehyde Schiff base (SSB), iso-PBP, PBP and EPB, were facilely synthesized and exhibited aggregation-induced emission. The introduction of C = N-N = C moiety in these SSB dyes largely extend the conjugation system and push their emission to yellow to red spectral region. These SSB dyes were negligibly fluorescent in dilute THF solution. In THF/water mixtures with high water fractions, they displayed strong yellow to red fluorescence (up to 617 nm) and large Stokes shifts (up to 152 nm). Single crystal analysis on EBP showed the longer emission of in aggregated state was attributed to the molecular packing effect as compared with that in dilute solution. The bio-imaging application indicated EBP could specifically accumulate in lipid droplets in living cells.