Investigation of triphenylene-based radical-containing ligand bridges in mediating electronic spin coupling and sensing chemical analytes

Abstract

Tritopic radical-containing ligand bridges are important components for the design of molecular and solid-state magnetic material, as they mediate strong spin exchange coupling between paramagnetic metals, and have potential for maintaining coherence at room temperature. In this thesis, the author explores ligand-mediated spin coupling and quantum properties of the tritopic radical bridge HXTP (HXTP = 2,3,6,7,10,11-hexa-substituted triphenylene). In the first part, a series of trimetallic complexes containing HXTP radical bridges are studied. Radical-mediated spin exchange between the metal centers, as well as the electronic delocalization across the HXTP ligands are investigated with combined crystallographic, spectroscopic, magnetic, and electrochemical techniques. Structurally resembling the building blocks of HXTP-based two-dimensional metal-organic frameworks (2D MOFs), these trimetallic complexes are further discussed as molecular models for the MOFs in the context of dimensional reduction. Moreover, the HXTP-centered radical with oxygen bridgehead atoms possesses long spin relaxation times at room temperature when integrated into a MOF matrix. The second part of the thesis explores such radicals as electronic spin qubits and their application as qubit sensors for chemical analytes. Chapter 1 provides an overview of the current research on HXTP-bridged trimetallic complexes and the dimensional reduction approach in the context of HXTP-based 2D MOFs. An overview of qubit-embedded MOF in the sensing of chemical analytes is also provided. Then, the author’s works are discussed in a broader context while providing possible future directions. Chapter 2 discusses synthesis and characterization of two tricopper HXTP complexes, where the HXTP-mediated spin coupling between paramagnetic metal centers was first quantified. Chapter 3 investigates the redox tuning of spin coupling in three trinickel complexes bridged by closed-shell, monoradical, and diradical HXTP ligands. Chapter 4 presents extremely strong magnetic coupling persistent at room temperature achieved in a trinickel HXTP complex with nitrogen bridgehead atoms. Finally, chapter 5 describes room-temperature quantitative detection of alkali metal ions using radical spin qubits in an HXTP MOF. Broader implications to the chemistry and quantum-related frontiers are also discussed.