Two reasonably designed polarity-viscosity sensitive fluorescent probes with large Stokes shift for lighting up lipid droplets in cells

Lipid droplets (LDs) are involved in a variety of complex life activities in cells, which are closely related to human diseases including obesity, diabetes and cancer. LDs are generally considered as a kind of organelle with extremely low water content and high viscosity. Herein, two novel probes (E)-2-(3-(2-(7-(diethylamino)-2-oxo-2H-chromen-3-yl)vinyl)-5,5-dimethylcyclohex-2-en-1-ylidene)malononitrile (LDP-1) and (E)-2-(3-(4-(diethylamino)styryl)-5,5-dimethylcyclohex-2-en-1-ylidene)malononitrile (LDP-2) were synthesized, which exhibited large Stokes shifts of 4758 cm−1 and 3986 cm−1 respectively. The two probes emitted strongly in hydrophobic and high viscosity environments. Moreover, bio-probes LDP-1 and LDP-2 exhibited low biological toxicity, and good selectivity. The two probes were also fit for selectively monitoring LDs distribution in living HeLa cells.