Towards Nano-Materials with Precise Control over Properties via Cluster-Assemblies*

One pathway towards nanomaterials with controllable band gaps is to assemble solids where atomic clusters serve as building blocks, because clusters' electronic structures vary with size, composition, and the charged state. To study the role of architecture in cluster assemblies, we synthesized multiple architectures of As$_{7}$$^{3-}$ clusters through controlling the counter-cations. Optical measurements revealed that the band gaps vary from 1.1-2.1 eV, even though the assemblies are constructed from identical cluster building blocks. First principles theoretical studies reveal that the variation is a result of altering the LUMO levels by changing the counter-cations. Additional variation in the gap is found by covalently linking the clusters with species of varying electronegativity to alter the degree of charge transfer. The findings offer a novel protocol for synthesis of nanoassemblies with tunable electronic properties.