Chromenylium Star Polymers: Merging Water Solubility and Stealth Properties with Shortwave Infrared Emissive Fluorophores

Fluorescence imaging in the shortwave infrared (SWIR) region has emerged as a vital tool for studying mammals. SWIR emissive polymethine dyes are well-suited to this endeavor; however, advancing <i>in vivo</i> imaging utility with these dyes is primarily limited by hydrophobicity and/or nonspecific protein association. Herein, we take a distinct approach to combine hydrophilicity and stealth behavior to construct bright, SWIR emissive chromenylium fluorophores by employing a well-defined poly(2-methyl-2-oxazoline) (POx) star polymer architecture, which we refer to as chromenylium stars, or "CStars." Of these polymer-shielded dyes, the variant containing five POx chains (<b>CStar30</b>) boasts particularly enhanced aqueous solubility and SWIR brightness, enabling high-resolution SWIR imaging in mice. The swift renal clearance and stealth behavior displayed <i>in vivo</i> also achieves improved noninvasive visualization of the lymphatic system. Further, CStar's orthogonal biodistribution to an FDA-approved dye, indocyanine green (<b>ICG</b>), facilitates excitation-multiplexed SWIR imaging in two colors to achieve simultaneous visualization of both fluid dynamics and protein dynamics in the same animal in real time at video-rate frame counts.