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

Abstract 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.