High fluorescence of carbazole derivatives for bioimaging of endoplasmic reticulum and lysosome: the influence of molecular structure on optical properties and cell uptake

Three new carbazole derivatives (L1–L3) with different functional groups have been synthesized and characterized. L1 and L2 are connected through methylene unit to construct L3 with enhanced molecular distortion configuration. The compounds exhibit dependent aggregation-induced enhanced emission (AIEE) properties and cellar uptake region in HepG2 cells. It is demonstrated that L1 and L2 exhibit modest AIEE properties in THF–H2O mixtures, while L3 shows superior AIEE character with 13 times enhancement. This is because of the enhanced molecular distortion configuration of L3 and the related restriction of π–π stacking interactions between adjacent L3 molecules resulted from the introduction of methylene unit. Due to the unique structure of the compounds, the superior fluorescence emission of L1–L3 in aqueous media, further imaging studies demonstrated the suitability of probes L1–L3 for the biological applications in both human liver hepatocellular carcinoma cells (HepG2) and plant tissues of Arabidopsis seedlings. The imidazole unit in L2 leads selective target to lysosome of HepG2 cells through acid–base interactions, while L1 and L3 are inclined to act with endoplasmic reticulum.