Acrylate-Substituted Thiadiazoloquinoxaline Yields Ultralow Band Gap (0.56 eV) Conjugated Polymers for Efficient Photoacoustic Imaging

Conjugated polymers have been proven to be full of promising application in photoacoustic (PA) imaging. Generally, the absorption spectra of PA contrast agents lying in the near-infrared (NIR) II window are requisite to eliminate the light absorption and scattering of tissue, skin, and blood. In this concise study, strong acceptor acrylate-substituted thiadiazoloquinoxaline (ATQ) was developed and used to copolymerize with different donors, yielding three NIR II polymers. Results show that (i) ATQ-based polymers can reach an ultralow optical band gap of 0.56 eV; (ii) the ATQ-based polymer nanoparticles have good biocompatibility and high PA signal intensity with a tissue penetration depth up to 10 mm; and (iii) under NIR II laser irradiation, the signal-to-noise ratio of mouse cerebrovascular during in vivo PA imaging enhanced by 10 times after injecting ATQ-based nanoparticles. This work reveals that acrylate-substituted ATQ-based polymers, which can be easily synthesized and functionalized, extend the absorption spectra to longer wavelengths, and decrease the radiative decay rate (kr), are a promising class of NIR polymers for developing efficient PA contrast agents.