Monitoring tumor growth with a novel NIR-II photoacoustic probe

In this chapter, we designed and synthesized a series of thiadiazoloquinoxaline (TQ)-based semiconducting polymers (SPs) with a broad absorption covering from NIR-I to NIR-II regions. Theoretical calculation suggests that the BTD-TQE with ester-substituted TQ-acceptor shows a large dihedral angle and narrow adiabatic energy as well as low radiative decay, resulting in higher reorganization energy for efficient photoinduced nonradiative decay (PNRD). As a result, the obtained BDT-TQE SP-cored nanoparticles, a NIR-II PA probe, exhibit a highest NIR-II photothermal conversion efficiency (61.6%) and achieved PA tracking of in situ hepatic tumor growth for 20 days. Herein, we propose a strategy to construct an effective NIR-II photoacoustic reagent through the enhanced PNRD effect of twisted intramolecular charge transfer (TICT), thereby extending the application of NIR-II PA reagents in in vivo bioimaging.