Near-infrared photosensitization via direct triplet energy transfer from lanthanide nanoparticles

Photosensitization under near-infrared (NIR) excitation is attractive for applications in photocatalysis and theragnostics because NIR light offers deeper penetration depth through various media, including biological tissues. Nevertheless, most photosensitization processes can only be stimulated by ultraviolet or visible light. Here, we demonstrate a new paradigm, based on the coupling of lanthanide inorganic nanoparticles and organic photosensitizers, for NIR photosensitization through lanthanide-triplet sensitization. We show that the triplet levels of a series of porphyrin and phthalocyanine sensitizers can be effectively populated by energy transfer from lanthanide nanoparticles. This approach allows to directly active lower-lying triplet states of photosensitizers without the need to populate their higher-lying excited singlet states. It enables photosensitization to generate singlet oxygen at ultralow NIR irradiance with over 100-fold improved performance compared with conventional upconversion-based NIR photosensitization, which may provide new opportunities for applications such as deep-tumor phototherapy and NIR-light driven photosynthesis.