Less Is More: Donor Engineering of a Stable Molecular Dye for Bioimaging in the NIR-IIb Window

Fluorescence molecular imaging aims to enhance clarity
in the region
of interest, particularly in the near-infrared IIb window (NIR-IIb,
1500–1700 nm). To achieve this, we developed a novel small-molecule
dye, named DA-5, based on classic cyanine dyes (heptamethine
or pentamethine is essential for wavelengths beyond 1000 nm). By reducing
excessive polymethine to a single methine and disrupting symmetry
to form an asymmetric donor-π-acceptor (D-π-A) architecture,
we enhanced the donor’s electron-donating capability, yielding
emission at 1088 nm. DA-5 exhibits superior properties,
including excellent chemo- and photostability, resistance against
solvatochromism-caused quenching, and antiaggregation in aqueous solution.
With a large Stokes shift (241 nm) and high brightness (321 M–1 cm–1), DA-5 enables
high-performance imaging of the lymphatic system, intestinal vessels,
whole-body angiography, and cerebral and hindlimb microvasculature
in NIR-IIb. This molecular design strategy offers a promising platform
for advancing in vivo biophotonics.