Surface Engineering of Atomically Precise M(I) Nanoclusters: From Structural Control to Room Temperature Photoluminescence Enhancement.

Abstract

ConspectusUnderstanding the structural architecture of nanoparticles is essential for investigating their fundamental properties because these materials have become more desirable in modern nanoscience research. Designing a proper synthetic strategy to control their growth with atomic precision is crucial. The polydispersed nature of the nanoparticles makes determining their precise structural information challenging. Metal nanoclusters (NCs) have emerged as a promising solution to this problem as they bridge the gap between metal nanoparticles and discrete molecular complexes. Well-ordered molecular structures provide opportunities to look at structure-property correlations and find quantum confinement effects at the atomic level that reveal their similarity to molecular-like properties. While most M(0)/(I)-based NCs exhibit exceptional photoluminescence (PL) emission at room temperature, M(I)-based NCs are less likely to exhibit PL emissions due to their electronic environment. Developments in the field of metal nanoparticles have made it intriguing to achieve room-temperature PL emission in M(I) NCs. Efforts have focused on developing efficient methods for preparing luminescent M(I) NCs to better comprehend fundamental aspects of their PL emission properties. We provide an overview of various synthetic strategies for preparing NCs and their selective functionalization for generating room-temperature PL emissions. Our focus has been creating an Ag(I) NC with a core-shell architecture, as this unique structural design complements the charge transition phenomenon. The molecular structure obtained from single-crystal X-ray diffraction (SCXRD) and associated theoretical calculation revealed that our effort results in a unique hexagonal closed pack core and Keplerate shell containing [S@Ag50S12(StBu)20]4+ NC where the charge transition between the core and the metal-ligand shell facilitates emission properties. We also explored the approach of host-guest supramolecular adduct formations to engineer the surface of ligands that reduce nonradiative relaxation rates by restricting surface molecular vibrations and controlling the generation of PL emission. To do this, we capped precisely structured [Cl@Ag16S(S-Adm)8(CF3COO)5(DMF)3(H2O)2]·DMF with β-cyclodextrin via adamantane moieties. We also describe the effects of bimetallic cluster formation on increasing surface rigidity and modulating the frontier molecular orbital arrangement, which helps to attain synergy to generate room-temperature PL emission. We focused on the structural integrity of Ag(I) NCs, allowing us to incorporate heterometal atoms at peripheral positions that lead to the formation of [CO2@Ag20Cu2S2(StBu)10(CF3COO)8(DMA)4]·(DMA). We also explored the impact of introducing extra ligands into the Ag(I) cluster node on the generation of PL emission at room-temperature. These strategies are not limited to Ag NCs. We discussed the possibility of combining core-shell architecture and surface modifications to enhance PL emission in [Cu18H3(S-Adm)12(PPh3)4Cl2] NC at room temperature. SCXRD studies revealed its distinct core-shell architecture that ensures electronic transitions and that transition is controlled by the imposed surface rigidity that yields a higher PL emission. We believe that this innovative structural engineering holds potential for the advancement of NC research, and this Account will inspire the scientific community to synthesize functional M(I) NCs.