The Influence of Passivating Ligand Identity on Au25(SR)18 Spin-Polarized Emission.

Magnetic circular photoluminescence (MCPL) spectra were collected following 3.1 eV excitation of two ligand-passivated Au25(SR)18 monolayer-protected clusters (MPCs). Both clusters generated spin-polarized emission; however, the degree of circular polarization noted for Au25(SC8H9)18, which was passivated with the aromatic phenylethanethiol ligand, was 5× that obtained for Au25(SC3)18, whose passivating ligand was aliphatic. Variable-magnetic field data were analyzed to determine Landé g-factors and spectroscopic term symbols for observable transitions contributing to the clusters' MCPL spectra. For Au25(PET)18, transitions originated from one doublet and two quartet fine-structure superatomic electronic states; by comparison, the Au25(SC3)18 spectrum contained only two components, both of which arose from doublet superatomic electronic states. Additionally, Faraday B-term contributions, which report on field-induced mixing, were more pronounced for Au25(SC3)18 spectral components. Therefore, the decreased spin-polarized emission by Au25(SC3)18 was attributed to stronger coupling to nonradiative decay channels. These results suggest the Au25(SR)18 cluster's passivating ligand can be used to tune the relative populations of emissive fine-structure states, the extent of mixing between radiative and nonradiative states, and the amplitude of spin-polarized emission in MPCs.