A Polyoxometalate Cluster Paradigm with Self-Adaptive Electronic Structure for Acidity/Reducibility-Specific Photothermal Conversion

Photothermal conversion is one of the most important keys in the fields of solar collection, photo-hyperthermia, etc., and its performance is highly dependent on the photothermal conversion materials used. Especially in cancer photo-hyperthermia, the presently available small-molecule- or nanomaterial-based agents still suffer from numerous drawbacks, such as nonspecific accumulation and inevitable side effects on normal tissues. Here we identify a Mo-based polyoxometalate cluster that can change its dimension from small (1 nm) to big (tens of nanometer), favoring its intratumoral accumulation, and enhance photothermal conversion in response to the intratumoral acidity and reducibility, demonstrating a previously unrealized tumor-specific photo-hyperthermia. Distinct from the well-researched nano-based agents, a unique electronic structure of this cluster has been identified as the origin of the observed acidity-induced self-assembly and reduction-promoted NIR absorbance. In addition to providing a promising clinical agent, this finding is expected to establish a new physicochemical paradigm for photothermal materials design based on clusters.