Lipid
droplets (LDs) are crucial organelles used to store lipids
and participate in lipid metabolism in cells. The abnormal aggregation
and polarity change of LDs are associated with the occurrence of diseases,
such as steatosis. Herein, the polarity-sensitive probe TBPCPP with
a donor–acceptor-π-acceptor (D-A-π-A) structure
was designed and synthesized. The TBPCPP has a large Stokes shift
(∼220 nm), excellent photostability, high LD targeting, and
considerable two-photon absorption (TPA) cross-section (∼226
GM), enabling deep two-photon imaging (∼360 μm). In addition,
the fluorescence lifetime of TBPCPP decreases linearly with increasing
solvent polarity. Therefore, with the assistance of two-photon fluorescence
lifetime imaging microscopy (TP-FLIM), TBPCPP has successfully achieved
not only the visualization of polarity changes caused by LD accumulation
in HepG-2 cells but also lipid-specific imaging and visualization
of different polarities in lipid-rich regions in zebrafish for the
first time. Furthermore, TP-FLIM revealed that the polarity gradually
decreases during steatosis in HepG-2 cells, which provided new insights
into the diagnosis of steatosis.