Constructing Stable and Wavelength-Extended Heptamethine Cyanines via Donor Ectopic Substitution for NIR-IIa/b Bioimaging

Abstract

Organic NIR-II dyes, particularly cyanine fluorophores, offer high molar extinction coefficients, biocompatibility, and structural tunability and are popular for noninvasive, high-resolution, and -contrast in vivo imaging. However, achieving stable, long-wavelength, and large Stokes shift NIR-II cyanine suitable for NIR-IIa/IIb bioimaging is still a formidable challenge. Herein, we introduce a novel strategy that extends the emission wavelength by the enhanced Highest occupied molecular orbital (HOMO)–Lowest occupied molecular orbital (LUMO) separation through simple donor ectopic substitution at the terminal structure of NIR-II cyanine. Compared to the original NIR-II cyanine Flav7, these novel dyes (NIR-ACs) exhibited a significant emission redshift and larger Stokes shift, with the maximum emission wavelength exceeding 1300 nm (NIR-IIa) and a tail emission exceeding 1500 nm (NIR-IIb). Notably, they also demonstrate excellent stability and deeper tissue imaging ability in vivo imaging. Finally, through surface modification of nanoparticles, NIR-ACs nanoparticles (NPs) have successfully achieved high-contrast tumor and bone-targeted detecting as well as multicolor imaging, providing robust tools for in vivo diagnostics and biomedical research.