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 Cu-I/Cu-II 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 (similar to 60 degrees C) and a temperature increment (similar to 40 degrees C), which are also superior to Cu(ii) complexes (the average equilibrium temperature similar to 55 degrees C). This work proves that it is possible to design and prepare new polynuclear mixed-valence Cu-I/Cu-II clusters for achieving high-performance photothermal conversion materials.