Multicolor Tuning of Perylene Diimides Dyes for Targeted Organelle Imaging In Vivo

The
adjustment of the emission wavelengths and cell permeability
of the perylene diimides (PDI) for multicolor cell imaging is a great
challenge. Herein, based on a bay-region substituent engineering strategy,
multicolor perylene diimides (MCPDI) were rationally
designed and synthesized by introducing azetidine substituents on
the bay region of PDIs. With the fine-tuned electron-donating ability
of the azetidine substituents, these MCPDI showed high
brightness, orange, red, and near infrared (NIR) fluorescence along
with Stokes shifts increasing from 35 to 110 nm. Interestingly, azetidine
substituents distorted to the plane of the MCPDI dyes,
and the twist angle of monosubstituted MCPDI was larger
than that of disubstituted MCPDI, which might efficiently
decrease their π–π stacking. Moreover, all of these MCPDI dyes were cell-permeable and selectively stained various
organelles for multicolor imaging of multiple organelles in living
cells. Two-color imaging of lipid droplets (LDs) and other organelles
stained with MCPDI dyes was performed to reveal the interaction
between the LDs and other organelles in living cells. Furthermore,
a NIR-emitting MCPDI dye with a mitochondria-targeted
characteristic was successfully applied for tumor-specific imaging.
The facile synthesis, excellent stability, high brightness, tunable
fluorescence emission, and Stokes shifts make these MCPDI promising fluorescent probes for biological applications.