Densely Fluorinated Polymer Dots with Peak Absorption beyond 1000 nm for High-Contrast NIR-II Fluorescence Imaging

Fluorescence probes in the second near-infrared (NIR-II) window hold promise for high-contrast optical imaging. However, it remains challenging to develop organic fluorophores with a peak absorption beyond 1000 nm. Here, we explore a dense fluorination strategy to tune the optical properties of semiconducting polymer toward the NIR-II region. The densely fluorinated polymer dots (Pdots) exhibit a peak absorption at ∼1040 nm and fluorescence at ∼1120 nm with a quantum yield of ∼1% in aqueous solution. A direct side-chain PEGylation facilitates the preparation of small Pdots of ∼25 nm diameter, while the hydrophobic fluorinated polymers tend to form nanoparticles larger than 150 nm. The small Pdots enabled in vivo fluorescence imaging via 1064 nm excitation and 1450 nm band-pass detection, while the Hessian-matrix processing method significantly enhances the image contrast of small blood vessels. This study indicates that the 1064 nm excitable Pdots are promising for in vivo fluorescence imaging of deep turbid tissues.