Design, Synthesis, and Imaging of a Stable Xanthene-Based Dye with NIR-II Emission up to 1450 nm.

The development of long-wavelength near-infrared II (NIR-II, 900-1700 nm) dyes is highly desirable but challenging. To achieve both red-shifted absorption/emission and superior imaging capabilities, a donor-acceptor-donor (D-A-D) xanthene core was strategically modified by extending π-conjugated double bonds and enhancing electron-donating properties. Two dyes named and were synthesized and exhibited notably red-shifted absorption/emission peaks at 942/1250 and 1098/1450 nm, respectively. Among them, demonstrated superior chemo- and photostability even at such long wavelengths. Fluorescent angiography using micelles enabled high-clarity blood vessel imaging with a remarkable signal-to-noise ratio (SNR), underscoring that the dye's large Stokes shift (352 nm), good brightness (13 M cm), and long wavelength served as key factors for high-quality biosensing. Additionally, combined with for dual-color imaging achieved near-zero optical cross talk, enabling different organ labeling. This study provides a new direction for the design of long-wavelength organic dyes.