A synergetic strategy of NIR-II squaraine dyes with ultrahigh photothermal conversion efficiency for photothermal therapy

Recent research on photothermal therapy (PTT) has sparked significant interest in the development of new organic photothermal agents (PTAs), ranging from single-molecule to aggregated levels. However, controlling aggregation pathways for PTAs with ultrahigh photothermal conversion efficiency (PCE) remains a major challenge. Herein, a two-pronged approach utilizing “H-aggregation” and “intramolecular motion” was employed to enhance the PCE of an acceptor-substituted squaraine dye (NSQs). The C2v molecular symmetry of the NSQs, which possess a ground state dipole moment (μg), promotes H-dimeric aggregates through dipole-dipole counteraction. Peripheral triphenylethylene or diphenylamine groups were added to this H-dimeric nanoplatform. This was done to enhance intramolecular motions for heat generation and also to extend conjugation, which red-shifted the optical absorption and balanced the blue-shift induced by H-aggregation. With this technique, an organic PTA with NIR-II absorption was developed, and its nanoparticle achieved a remarkable PCE of 86.3