Enhanced Photothermal Therapy under Low-Power Near-Infrared Irradiation Enabled by a Si-Cyclopentadithiophene-Based Organic Molecule.

Due to the inadequate photothermal conversion efficiency (PCE), most photothermal agents (PTAs) have to be used under high-power near-infrared (NIR) irradiation, which significantly exceeds medical safety standards, for achieving effective photothermal therapy (PTT) in antitumor treatment. This significantly hinders practical PTT application. Herein, three acceptor-donor-acceptor(A-D-A)-type molecules are synthesized based on cyclopentadithiophene unit to develop effective PTAs. By incorporating the large-size Si atom in the A-D-A molecules, the photosensitizer displays an increased packing distance in the aggregate state, leading to a blue-shifted absorption spectrum that better matches the medial laser wavelength. Also, the Si incorporation strategy elevates the nonradiative decay rate constants (k_nr) of the A-D-A photosensitizer, and thereby a further enhancement in PCE is achieved for the PTA. Consequently, the SiO-4F-based nanoparticles exhibited 64.23% PCE, with excellent biosafety and photothermal stability. Under NIR irradiation with medical safety (808 nm, 0.33 W cm^-2), SiO-4F nanoparticles with 100 µg mL^-1 yield a death rate of over 91% for diverse tumor cells. Moreover, in vivo experiments, SiO-4F-based PTT effectively inhibited and eliminated tumors. These findings suggest that the Si-incorporated CDPT is promising for constructing effective A-D-A photosensitizers, enabling the PTT under NIR irradiation that meets medical safety standards.