PhD Prospectus Defense: Zelin Miao

PhD Prospectus Defense: Zelin Miao

TITLE: Incorporating Paramagnetic Molecular Wires into Single-Molecule Circuits

ADVISOR: Masha Kamenetska Chem, Physics, MSE

COMMITTEE: Linda Doerrer Chem, MSE; Sahar Sharifzadeh ECE, MSE, Chem; Joerg Werner ME, MSE, Chem

ABSTRACT: The push to miniaturize electrical circuits has motivated the search for molecular materials that could serve as active components in future electronic devices. While many studies have focused on neutral, close-shell organic molecular systems, integration of paramagnetic molecules into metal-molecule-metal junctions presents opportunities for exploring the electronic and spintronic properties and applications of molecules. Here, I explore strategies for forming molecular junctions incorporating metal ions and organic radicals. Recent single molecule conductance studies have shown that in situ incorporation of electrode metal atoms (e.g., Au) into coordination chains formed in the junction can occur with deprotonated, negatively charged organic ligands, such as imidazolate (Im-) anion. However, the mechanism and chemical principles behind are still unclear. In the first part of proposed project, I probe the role of the ligand charge state and electronic structure in the formation of metal-molecule coordination chains with gold atom. We perform break junction measurements with triazole isomers, which can bridge junctions both in their neutral and charged forms, and find that prior deprotonation of the ligands is not required for coordination complex assembly with gold ions. Instead, our results emphasize that the electron density distribution within the molecule is a more significant determinant than the overall ligand charge state.

Next, I will demonstrate a new electrochemical conductance measurement which leads to in situ assembly of coordination chains containing group 11, coinage transition metals, such as silver and copper. Specifically, I show data suggesting successful formation of Im- coordination chains containing Ag(I) and Cu(II) at tip of the STM break junction in polar aprotic organic solvent propylene carbonate (PC), alongside previously observed results for Au (I). These findings, supported by first-principle density functional theory (DFT) calculations, suggest that open-shell junctions, such as those containing Im-Cu(II)-Im can be assembled under ambient conditions and offer insights into design principles for in situ assembly of coordination wires. I will also discuss briefly how the charge transport properties and spin state of a class of dTMeS organic diradicals can be modulated by applying an electric field and altering the solvent environments. These results open the door to further electronic and spintronic studies of such materials.