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 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 fluorescence imaging of deep turbid tissues.