Monocarboxylate-protected two-electron superatomic silver nanoclusters with high photothermal conversion performance.

The first series of monocarboxylate-protected superatomic silver nanoclusters was synthesized and fully characterized by X-ray diffraction, fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and electrospray ionization mass spectrometry (ESI-MS). Specifically, compounds [Ag16(L)8(9-AnCO2)12]2+ (L = Ph3P (I), (4-ClPh)3P (II), (2-furyl)3P (III), and Ph3As (IV)) were prepared by a solvent-thermal method under alkaline conditions. These clusters exhibit a similar unprecedented structure containing a [Ag8@Ag8]6+ metal kernel, of which the 2-electron superatomic [Ag8]6+ inner core shows a flattened and puckered hexagonal bipyramid of S6 symmetry. Density functional theory calculations provide a rationalization of the structure and stability of these 2-electron superatoms. Results indicate that the 2 superatomic electrons occupy a superatomic molecular orbital 1S that has a substantial localization on the top and bottom vertices of the bipyramid. The π systems of the anthracenyl groups, as well as the 1S HOMO, are significantly involved in the optical and photothermal behavior of the clusters. The four characterized nanoclusters show high photothermal conversion performance in sunlight. These results show that the unprecedented use of mono-carboxylates in the stabilization of Ag nanoclusters is possible, opening the door for the introduction of various functional groups on their cluster surface.

Construction of eight mixed-valence pentanuclear CuI4CuII clusters using ligands with inhomogeneous electron density distribution: synthesis, characterization and photothermal properties.

To enhance light absorption in the visible region for the utilization of sunlight, eight mixed-valence polynuclear CuI/CuII clusters have been synthesized for evaluating their photothermal conversion performance. They are fabricated considering the ligand's electron density distribution inhomogeneity using 1,2,3-triazole (3N) or tetrazole (4N) and different mono-phosphine ligands. We report here the synthesis, crystal structure, characterization, optical properties, and photothermal conversion performance of these clusters. X-ray crystal structures reveal that those pentanuclear clusters are neutral clusters with octahedrally-coordinated copper(II) ion being surrounded by four tetrahedrally coordinated copper(I) ions. Interestingly, with the introduction of the mixed-valence centers, these compounds show additional light absorption centers in 350-600 nm via the IVCT transition mechanism, compared with our previously reported Cu(II) compounds. These clusters show excellent photothermal conversion performance, with an average equilibrium temperature (∼60 °C) and a temperature increment (∼40 °C), which are also superior to Cu(II) complexes (the average equilibrium temperature ∼55 °C). This work proves that it is possible to design and prepare new polynuclear mixed-valence CuI/CuII clusters for achieving high-performance photothermal conversion materials.