“Crossbreeding” Small-Molecular Weight NIR-II Flavchromenes Endows Activatable Multiplexed In Vivo Imaging

High-performance near-infrared-II (NIR-II) fluorophores
have attracted
tremendous attention for in vivo dynamic bioimaging. However, the
lack of stable, bright, and biocompatible molecular fluorophores becomes
a major barrier on the way to the widespread endorsement of NIR-II
bioimaging for clinic diagnosis. Here we propose a π-conjugated
“crossbreeding” dyad strategy to develop novel desirable
NIR-II dyes, flavchromenes (flav+chromene) integrated from two individual
fluorophores of flavylium and chromene via a short methine bridge,
affording valuable features of extending spectra into the NIR-II region
and conferring a substantive leap in the photophysical properties.
Notably, these crossbreeding NIR-II dyes have small molecular weights,
high molar extinction coefficients, and outstanding chemical stability.
As demonstrated, the elaborated probe Flavchrom-4 endows activatable
dual-modal in vivo imaging of endogenous β-galactosidase activity,
along with lighting-up NIR-II fluorescence signals and dramatically
enhanced photoacoustic signals (16.3-fold). This concise π-conjugated
crossbreeding dyad strategy brings forth high-performance NIR-II fluorophore
scaffolds with small molecular weights, high stability, and good brightness,
thus greatly expanding high-resolution activatable in vivo imaging
tools for intact tissues and living animals.