Conjugated Oligoelectrolytes for Long‐Term Tumor Tracking with Incremental NIR‐II Emission

The design and synthesis of the near-infrared (NIR)-II emissive conjugated oligoelectrolyte COE-BBT are reported. COE-BBT has a solubility in aqueous media greater than 50 mg mL-1 , low toxicity, and a propensity to intercalate lipid bilayers, wherein it exhibits a higher emission quantum yield relative to aqueous media. Addition of COE-BBT to cells provides two emission channels, at ≈500 and ≈1020 nm, depending on the excitation wavelength, which facilitates in vitro confocal microscopy and in vivo animal imaging. The NIR-II emission of COE-BBT is used to track intracranial and subcutaneous tumor progression in mice. Of relevance is that the total NIR-II intensity increases over time. This phenomenon is attributed to a progressive attenuation of a COE-BBT self-quenching effect within the cells due to the expected dye dilution per cell as the tumor proliferates.