UC Berkeley

This dissertation explores how low-energy electronic states in molecular and coordination networks can be deliberately engineered and probed at the atomic scale. Using a combination of bottom-up synthesis, on-surface assembly, and low-temperature scanning tunneling microscopy and spectroscopy (STM/STS), I investigate how symmetry, topology, and local chemical environment control band edges, metallic channels, and symmetry-breaking instabilities in low-dimensional quantum materials.I first introduce a one-dimensional π-conjugated polymer, poly(difluorenoheptalene-ethynyl-ene) (PDFHE), in which a pseudo–Jahn–Teller (PJT) mechanism drives a collective distortion of the backbone. By combining on-surface synthesis, bond-resolved STM (BRSTM), and density functional theory (DFT), I show that the combination of non-benzenoid difluoreno-heptalene units and ethynylene linkers produces frontier states of the appropriate symmetry to undergo strong PJT vibronic coupling. This coupling destabilizes the high-symmetry structure, driving a collective symmetry-lowering distortion that splits the frontier bands and reshapes the electronic band gap.I then turn to graphene nanoribbons (GNRs) as a platform for semiconducting and metallic one-dimensional (1D) channels. For N = 8 armchair GNRs (8-AGNRs), I use solution-phase A2B2 Suzuki polymerization combined with matrix-assisted direct (MAD) transfer and on-surface cyclodehydrogenation on Au(111) to realize structurally precise ribbons with an experimentally measured band gap of 0.74 ± 0.04 eV, in the technologically relevant range between silicon and germanium. Beyond this, I develop an engineered a 5-membered-ring-decorated 7-AGNR (H2-7-iGNR) that can be toggled from a gapped semiconductor to a robust two-channel metal (7-iGNR) by STM-induced edge dehydrogenation. Wannier analysis of the metallic state maps its frontier bands onto an extended Su–Schrieffer–Heeger zigzag ladder model, and local dehydrogenation within a single ribbon yields atomically sharp metal-semiconductor junctions with nearly barrierless p-type alignment.Moving beyond purely carbon-based systems, I introduce organometallic lattices based on N-heterocyclic carbene (NHC) ligands coordinated to Au. Linear NHC–Au–NHC junctions are assembled into 1D chains and two-dimensional (2D) Kagome-type lattices on Au-based substrates. STM/STS and DFT show that C–Au–C bonding states hybridize into dispersive bands that cross the Fermi level, imparting intrinsic metallicity and exceptionally low work functions comparable to alkali metals, but realized here in structurally well-defined molecular networks.Finally, I describe ongoing work on Kagome-type metal–organic frameworks (MOFs), exemplified by monolayer Ni3(HITP)2 grown on van der Waals substrates using a metal-salt-based chemical vapor epitaxy (CVE) approach. STM imaging confirms the Kagome coordination network and monolayer character on HOPG and WSe2, while STS combined with DFT and GW calculations reveals an isolated Kagome band manifold with identifiable flat bands on both the conduction and valence sides. When grown on graphene/hBN field-effect devices, the valence-side flat band can be shifted relative to the Fermi level by electrostatic gating, establishing a gate-addressable molecular Kagome flat band on a device-compatible platform.Across these systems, common design principles emerge: exploiting symmetry and its breaking, tuning backbone topology and ring chemistry, controlling edge and coordination environments, and carefully managing substrate coupling. Together, the results demonstrate a progression from 1D polymers and nanoribbons to organometallic lattices and 2D MOFs, all viewed through the common lens of low-energy electronic states engineered by molecular design and interrogated by local spectroscopy. The methods and concepts developed here lay a foundation for actively steering low-energy states in designer molecular networks toward targeted functionalities in future quantum devices.