Two- and Three-Dimensional Silver Cluster Assemblies: Effect of Argentophilic Interactions in Photoluminescence

Silver nanocluster assemblies are an emerging class of fluorescent and stable solid materials by virtue of their structural tunability and stability compared to isolated clusters. The photophysical properties of the cluster nodes are influenced by an intra- or intercluster interaction. In this work, we show two-dimensional (2D) [Ag₅(C₂^<i>t</i>Bu)₂(CF₃COO)₃(C₄H₄N₂)](CHCl₃) and three-dimensional (3D) [Ag₄(C₂^<i>t</i>Bu)(CF₃COO)₃(C₄H₄N₂)] silver nanocluster assemblies obtained by tuning the molar ratios of the same protecting ligands and linker. The 2D assembly possesses a one-dimensional (1D) chain held together through the Ag···Ag interactions, whereas in the 3D assembly, Ag₄ units are linked through trifluoroacetate ligands to form the 1D chain with Ag₄-O-Ag₄ and Ag₄-O-C-O-Ag₄ connectivity. This varying effect of argentophilic interaction influences photoluminescence properties. In the 2D assembly, the emission was found to be dominated by the cluster-centered state owning to enhanced argentophilic interactions, whereas in 3D, the emission is from the linker. The theoretical investigations also revealed that the lowest unoccupied molecular orbitals (LUMOs) of the 3D assembly are localized on the pyrazine linker. In contrast, the LUMOs of the 2D assembly are mostly localized on the metal atoms within the cluster. This work highlights not only the importance of synthesis but also emphasizes the understanding of the cluster structure-luminescence relationship.