Rational Approaches to Achieve Luminescent Gold Clusters for Optical Applications

Date of Award

8-2025

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Ramakrishna Guda, Ph.D.

Second Advisor

Gellert Mezei, Ph.D.

Third Advisor

David Huffman, Ph.D.

Fourth Advisor

Asghar Kayani, Ph.D.

Keywords

Gold nanoclusters, photoluminescence, spectroscopy, ultrafast transient absorption

Abstract

Over the past two decades, quantum-sized gold clusters have emerged as ultra-small nanomaterials with intriguing photophysical characteristics, such as good photostability, long luminescence lifetimes, and large two-photon cross sections. Their molecule-like behavior, good biocompatibility, and high atomic precision reinforce their potential for varied optical applications. Their blink-less emission feature, owing to the strong coupling between the metal core and surface ligands, makes them superior to the well-recognized semiconductor quantum dots, as they are more reliable for single particle tracking. Nevertheless, their low Photoluminescence Quantum Yields (PLQY) compared to dyes, semiconductor quantum dots, and other luminescent materials hinder their utilization in practice. For water-soluble gold clusters, retaining their water solubility is difficult with photoluminescence enhancement strategies such as ion pairing with bulky substituents, aggregation in polar organic solvents, and all chromophore functionalization, thereby preventing their utilization for aqueous applications. Another challenge is the electrochemical profiling of water-soluble clusters in aqueous media due to lower peak resolution associated with water-soluble shells and the narrow potential window of water.

This work demonstrates strategies for enhancing the photoluminescence of thiol-protected gold nanoclusters, for both retained and varied solubilities. The first strategy employs flexible soft matter system-based confinements of the glutathione and captopril-protected clusters, including self-assemblies of reverse micelles and Small Unilamellar vesicles. While reverse micelle systems can be utilized for indirect sensing applications, the vesicle systems are highly biocompatible. The second strategy involves the Photoluminescence enhancement of clusters upon dye functionalization. Ligand exchange reactions with dye-functionalized thiol were performed to facilitate functionalization. Transient Absorption analysis revealed the electron-transfer/ energy-transfer processes occurring at the dye/cluster interface, leading to enhancement/quenching of the cluster’s luminescence. Various chromophore-functionalized gold clusters were synthesized and characterized. Ultrafast transient absorption and anisotropy measurements were able to probe the dynamics of charge transfer interactions at the interface of the cluster and dye. To achieve maximum PL enhancement at room temperature by suppressing kernel and shell vibrations, attempts were performed to cast thin films of water-soluble polymers to obtain smooth solid films that are device-ready for photonic applications, leading to a manifold increase in their emissions.

Access Setting

Dissertation-Abstract Only

Restricted to Campus until

8-1-2027

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