Controlling the Supramolecular Assembly and Photophysical Properties of Atomically Precise Metal Chalcogenide and Noble Metal Nanoclusters

Abstract

Noble metals such as gold and silver—when confined to the nanoscale (1–100 nm)—enable control of electromagnetic fields in the sub-wavelength size regime. This property has pioneered state-of-the-art technologies spanning telecommunications, light harvesting, and medical treatment. However, one underlying challenge in understanding the origin of these phenomena is that no two nanoparticles are the same: inherent heterogeneity in nanoparticle size, shape, and surface morphology create ambiguity when correlating function to structure. When confined to the ultrasmall size regime (1–3 nm), nanoparticles can be synthesized with atomic precision—often termed atomically precise nanoclusters (NCs)—enabling their purification and crystallization as molecular entities, thereby providing nanoparticles with exact uniformity in size, shape, and composition. However, harnessing these atomically precise properties in functional materials has proved difficult. The work presented in this dissertation establishes a strategy to precisely assemble nanoclusters into crystalline materials which exhibit unique supramolecular architectures and optical behaviors. Chapter One introduces a brief history of colloidal nanochemistry from its original scientific investigation to the current state of the art. The emergence of atomically precise NCs as an answer to the heterogeneity problem is then discussed as highlighted by their catalytic and optical properties. Precedent for NC-based materials and their design challenges are described, and a potential strategy to overcome these challenges is then presented. In Chapter Two, I discuss structure-property relationships for NCs towards catalytic CO2 electroreduction. Using a new series of silver NCs and their comparison to established structures, a facile computational method is developed to express NC surface accessibility towards specific substrates, providing excellent agreement with their measured catalytic activity. This method provides a new descriptor and qualitative heuristic for NC structure-property correlation. Chapter Three examines a novel approach to control NC assembly. Using single-valence silver clusters as structural surrogates for zero-valence NCs, triangulene platforms are employed to direct their cocrystallization and superlattice arrangement. Developing a new, slow-nucleation strategy for silver cluster synthesis, clusters with nuclearities spanning an order of magnitude are prepared and can assemble with the triangulene directing agent. These hybrid cocrystals are interrogated with steady-state and time-resolved photoluminescence microspectroscopy which reveal cluster-to-triangulene energy transfer and exciton coupling between the triangulenes. Chapter Four extends this methodology to zero-valence silver NCs, exploring the effects of triangulene helical distortion and symmetry breaking on the superlattice morphology and NC interactions. By precisely tuning this interaction, NC-based near-infrared enhancement up to three orders of magnitude can be achieved, and mechanistic insight is garnered by time-resolved photoluminescence and quantum chemical simulation. Finally, Chapter Five explores an evolution in superlattice assembly when the triangulene footprint size is adjusted. Using achiral silver NCs and achiral triangulenes, the cocrystal assemblies evolve from achiral to racemic to chiral, demonstrating chirogenesis originating from these precise supramolecular interactions. These structures are examined with fluorescence-detected circular dichroism, exhibiting very high chiroptical dissymmetry factors.