Interface Electronic Properties Between a Gold Core and Thiolate Ligands: Effects on an Optical Absorption Spectrum in Au133(SPh-tBu)52

Abstract

We analyze the electronic structures and optical absorption spectrum of Au133(SPh-tBu)52, particularly in terms of interface electronic properties between the Au core and the thiolate ligands. Computations are performed by using the time-dependent density functional theory approach in real-time and real-space that has recently been developed by our group. Local density of states analysis reveals a relationship between an icosahedral Au core and a thiolate-protected Au cluster; Au atoms associated with the edge or surface sites of the icosahedral core anchor the ligands to the core, whereas Au atoms associated with the apex sites bridge two thiolates forming −S–Au–S– bonds. We compare the optical absorption spectrum of Au133(SPh-tBu)52 with that of an icosahedral Au146 bare cluster to clarify effects of the ligands on the optical absorption. The absorption intensity for Au133(SPh-tBu)52 is obviously higher than that for the bare cluster. The significant increase in the optical absorption of Au133(SPh-tBu)52 is attributed to mutual enhancement of electric polarizations induced both in the Au core and in the thiolate ligands. The effect of the enhancement is computationally visualized by analyzing the electric fields generated in the Au core and the thiolate ligands.