Spectral and biodistributional engineering of deep near-infrared chromophore

Fluorescence-guided surgery calls for development of near-infrared fluorophores. Despite the wide-spread application and a safe clinical record of Indocyanine Green (ICG), its maximal absorption wavelength at 780 nm is rather short and longer-wavelength dyes are desired to exploit such benefits as low photo-toxicity and deep penetration depth. Here, we report ECY, a stable deep near-infrared (NIR) fluorochromic scaffold absorbing/emitting at 836/871 nm with a fluorescence quantum yield of 16% in CH₂Cl₂. ECY was further rationally engineered for biological distribution specificity. Analogous bearing different numbers of sulfonate group or a polyethylene glycol chain were synthesized. By screening this focused library upon intravenous injection to BALB/c mice, ECYS2 was identified to be a suitable candidate for bioimaging of organs involved in hepatobiliary excretion, and ECYPEG was found to be a superior candidate for vasculature imaging. They have potentials in intraoperative imaging.