Cluster-assembled materials: Toward nanomaterials with precise control over properties

One pathway toward nanomaterials with controllable band gaps is to assemble solids where atomic clusters serve as building blocks, since the electronic structures of clusters vary with size and composition. To study the role of organization in cluster assemblies, we synthesized multiple architectures incorporating As ₇ ^3- clusters through control of the countercations. Optical measurements revealed that the band gaps vary from 1.1-2.1 eV, even though the assemblies are constructed from the identical cluster building block. Theoretical studies explain this variation as being a result of altering the lowest unoccupied molecular orbital levels by changing the countercations. Additional variations in the gap are made by covalently linking the clusters with species of varying electronegativity to alter the degree of charge transfer. These findings offer a general protocol for syntheses of nanoassemblies with tunable electronic properties.