posted on 2023-11-15, 13:04authored byShana Havenridge, Christine M. Aikens
Alkynyl-protected
gold clusters have recently gained attention
because they are more structurally versatile than their thiolate-protected
counterparts. Despite their flexibility, however, a higher photoluminescent
quantum yield (PLQY) has been observed experimentally compared to
that of organically soluble thiolate-protected clusters. Previous
experiments have shown that changing the organic ligand, or R group,
in these clusters does not affect the geometric or electronic properties
of the core, leading to a similar absorption profile. This article
serves as a follow-up to those experiments in which the geometric,
optical, and photoluminescent (PL) properties of Au22(ETP)18 are pieced together to find the photoluminescence mechanism.
These properties are then compared between Au22(CCR)18 clusters where the ligand is changed from R = ETP to PA
and ET (ETP = 3-ethynylthiophene, PA = phenylacetylene, and ET = 3-ethynyltoluene).
As the theoretical results do not reproduce the same absorption profile
among the different ligands as in the experiment, this article also
presents a supplementary benchmark of the geometric and optical properties
among the three ligands for different levels of theory. The calculations
show that the photoluminescence mechanism with the ETP ligand results
in ligand-to-metal-to-metal charge transfer (LMMCT), while PA and
ET are likely a result of core-dominated fluorescence. The changes
are the result of the Au(I) ring atoms as well as how the aromatic
groups are connected to the cluster. Additionally, dispersion, solvent,
and polarization functions are all important to creating an accurate
chemical environment, but the most useful tool in these calculations
is the use of a long-range-corrected exchange-correlation functional.