Nanomaterials that generate reactive oxygen species (ROS) upon light irradiation play crucial roles in a plethora of areas, such as photocatalysis, pollution treatment, fine chemical synthesis, and photodynamic therapy (PDT). (1−4) However, most of these materials lack the capability to be excited by light of relatively long wavelength, especially near-infrared (NIR) light. For example, nanosemiconductors such as TiO2, which are commonly used in photocatalysis, respond to wavelengths shorter than 387.5 nm because they have a band gap of 3.2 eV. (5) By engineering of defect energy levels, the absorption could be marginally expanded to over 400 nm. (6−8) The efficiency of utilizing sunlight would therefore be limited, as visible and NIR light accounts for over 90% of the energy of solar radiation. (9,10) In parallel, most organic photosensitizers employed in PDT are excited by wavelengths shorter than approximately 700 nm. (11,12) Because visible light cannot easily penetrate biotissues, (13) a metal-containing tetrapyrrolic photosensitizer, padeliporfin, was developed to function under NIR irradiation (λex = 753/763 nm), (14,15) initiating the exploration of long-wavelength-light stimulation. Furthermore, a few molecules/nanoparticles, such as indocyanine green (16) and CuS, (17,18) have been discovered to generate ROS upon NIR irradiation, although the absorbed energy would be partially consumed by the photothermal effect. (19) Alternatively, upconversion nanoparticles have been applied as the carriers of classical photosensitizers, resulting in ROS production under irradiation with NIR lasers. (20−22) Despite this progress, it should be mentioned that no single sensitizer or light source is ideal for all applications. (4) Therefore, seeking alternative ROS-generating materials that can be stimulated by NIR light is still warranted for diverse applications.
