Date of Award

2026-08-01

Degree Name

Doctor of Philosophy

Department

Chemistry

Advisor(s)

Sreeprasad T. Sreenivasan

Abstract

Predicting function in low-dimensional materials are often framed in terms of the composition of an active site, transport channel, or spin center. However, as functional units are reduced to the single-entity limit - a single molecule, a single electron, or a single spin - their behavior becomes increasingly governed by the local environment to which they are coupled. Interfaces, edges, disorder landscapes, confinement, and coordination environments can exert a stronger influence on performance than the identity of the active site itself. This dissertation examines how local environment coupling governs charge transfer, sensing response, charge localization, and spin coherence across a series of low-dimensional material systems and establishes environmental engineering as a unifying design strategy for controlling function. The first two studies focus on activating and amplifying charge-transfer processes. Chapter 2 investigates a graphene-supported single-molecule oxygen evolution catalyst based on the dichloro(1,3-bis(diphenylphosphino)propane) nickel (NiCl2dppp) coordination complex. Although catalytic performance would traditionally be attributed to the metal center, interfacial charge transfer between the molecule and graphene acid is shown to activate the Ni site, while an operando structural transformation generates a field-responsive paramagnetic state. The resulting field-dependent enhancement is consistent with a spin-sensitive interfacial contribution to oxygen evolution catalysis. Chapter 3 examines molecular sensing for perfluorooctanoic acid (PFOA) in individual graphene nanoribbon field-effect transistors (FETs). While sensor performance is often associated with surface area or molecular binding affinity, the dominant variables are shown to be ribbon width, edge structure, reduced electrostatic screening, and fringe-field concentration. Controlled edge roughness enhances molecular anchoring and charge-transfer efficiency, producing an effective coverage-normalized response of approximately 116 ± 10 mV per molecule for the narrowest ribbons.

The final two studies focus on localizing and preserving electronic and spin states. Chapter 4 investigates lithographically defined graphene nanoribbon devices containing embedded graphene-island geometries. Although the lithographic geometry might be expected to determine charging behavior, the dominant factor is shown to be the electrostatic disorder landscape created by edge morphology and local charge inhomogeneity. Smooth constrictions exhibit cleaner Coulomb blockade characteristics and larger effective localized-island charging-energy descriptors, whereas rougher devices produce fragmented, disorder-dominated transport. Chapter 5 examines coherence in oxygen-coordinated Cu(II) qubit-candidate metal–organic frameworks. Rather than being governed primarily by Cu···Cu separation, spin relaxation and phase-memory behavior are found to depend strongly on framework connectivity, proton density, hydrogen bonding interactions, and lattice rigidity. A two-dimensional Cu-TPTriC ([1,1':4',1" terphenyl] 3,4",5 tricarboxylic acid), framework exhibits longer relaxation and coherence times than the structurally related one-dimensional Cu-TPTC ([1,1':4',1"-terphenyl] 3,3",5,5"-tetracarboxylic acid) framework despite possessing shorter Cu···Cu distances. Together, these studies show that the local environment often becomes the dominant design variable at the single-entity limit. Interfaces activate molecular catalysts, edges amplify sensing signals, disorder landscapes determine charge localization, and coordination environments preserve spin coherence. Importantly, the same environmental feature can enhance or degrade performance depending on the targeted function: edge roughness improves molecular sensing yet destabilizes single-electron transport. These results establish three general design principles: functional interfaces can outweigh active-site composition, environmental disorder must be matched to the desired function rather than universally minimized, and connectivity and secondary-sphere structure can govern quantum behavior more strongly than simple geometric distance. Collectively, this work demonstrates that deliberate engineering of local environments provides a powerful framework for controlling charge-transfer, single-electron, and spin dependent phenomena in low-dimensional materials.

Language

en

Provenance

Received from ProQuest

File Size

336 p.

File Format

application/pdf

Rights Holder

Kavish Saini

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Included in

Chemistry Commons

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