Convenient construction of fluorescent markers for lipid droplets with 1,8-naphthalimide unit

1,8-Naphthalimide is widely applied in the construction of probes because it is easy to be modified. However, 1,8-naphthalimide has been reported rarely in the application of organelle labelling especially lipid droplets (LDs). Herein, three types of amine compounds, aliphatic amine ( a , b ), aromatic amine ( c , d ) and heterocyclic amine ( e , f ), were chosen to construct fluorescent dyes ( 1a - 1f ) with 4-bromo- N -butylnaphthalimide ( 1 ) by Ullmann reaction. The maximum emission wavelength ranged from 490 nm to 550 nm. What's more, 1a-1e showed high fluorescence quantum yields (0.54–0.93) in chloroform and 1e-1f had excellent photostability (>92%). In addition, the cell imaging experiment showed that they could label lipid droplets for HeLa cancer cells and L929 normal cells with extremely low toxicity. This work realizes the classical fluorophore 1,8-naphthalimide to synthesize a series of LDs markers without complex synthesis steps.