The photothermal properties of a series of neutral radical gold-bis(dithiolene) complexes absorbing in the near-infrared-III window (1550-1870 nm) have been investigated. This class of complexes was found to be good photothermal agents (PTAs) in toluene under 1600 nm laser irradiation with photothermal efficiencies around 40 and 60 % depending on the nature of the dithiolene ligand. To the best of our knowledge, these complexes are the first small molecular photothermal agents to absorb so far into the near infrared. To test their applicability in water, these hydrophobic complexes have been encapsulated into nanoparticles constituted by amphiphilic block-copolymers. Stable suspensions of polymeric nanoparticles (NPs) encapsulating the gold-bis(dithiolene) complexes have been prepared which show a diameter around 100 nm. The encapsulation rate was found to be strongly dependent on the nature of the dithiolene ligands. The photothermal properties of the aqueous suspensions containing gold-bis(dithiolene) complexes were then studied under 1600 nm laser irradiation. These studies demonstrate that water has strong photothermal activity in the NIR-III region that, cannot be overcome even with the addition of gold complexes displaying good photothermal properties.
Keywords: Gold-bis(dithiolene) complexes; Molecular photothermal agent; NIR-III Laser irradiation; Nanoparticles; Photothermal index.
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