Optical Properties of Monolayer-Protected Aluminum Clusters: Time-Dependent Density Functional Theory Study

Abstract

We examine the electronic and optical properties of experimentally known monolayer-protected aluminum clusters Al4(C5H5)4, Al50(C5Me5)12, and Al69(N(SiMe3)2)183– using time-dependent density functional theory. By comparing Al4(C5H5)4 and the theoretical Al4(N(SiMe3)2)4 cluster, we observe significant changes in the optical absorption spectra caused by different hybridization between metal core and ligands. Using these initial observations, we explain the calculated spectra of Al50(C5Me5)12 and Al69(N(SiMe3)2)183–. Al50(C5Me5)12 shows a structured spectrum with clear regions of low-intensity core-to-core transitions followed by high-intensity ligand-to-core transitions due to its high symmetry and π-bonding to the Cp ligands. The spectrum of Al69(N(SiMe3)2)183– is rather featureless as the core-to-core and ligand-to-core regions partially merge because of the lower symmetry found in the metal core and differences in the ligand–core hybridization. Though there are minimal features in the spectra, the most i...