Manipulating the coupling between electronic and spin degrees of freedom in molecules

The miniaturisation of semiconductors is running into physical limitations. In order to further enhance computational powers, reaching the atomic or molecular level is both necessary and inevitable. At the nanometre scale, the quantum properties of materials become important. These can be used for qubits in quantum computers, which are able to process information significantly faster than traditional counterparts. One approach towards such novel nanoelectronic devices is realised via molecular magnetic materials. Single-molecule magnets, which represent the smallest possible molecular magnetic structures, are currently being tested in such devices. However, the physics of these materials is not yet completely understood. The magnetic property of electrons, known as the electron spin, plays a crucial role here. It is furthermore very sensitive to its surroundings. Interactions with neighbouring nuclear spins, for instance, lead to decoherence, which translates to a loss of stored quantum information. In order to promote the development of new elements for nanoelectronics or qubits, it is therefore essential to unravel the couplings of the spins and their surroundings, and learn how to control and manipulate them. The present work focuses on how light, as an ultra-clean technique, can be used to manipulate the molecular spin states, and how magnetic centres interact when chemically attached to a graphene nanoribbon. We employ state-of-the-art electron spin resonance techniques and SQUID magnetometry to investigate the effect of light on a new cobalt valence tautomer, where we find an enhanced blocking temperature of a metastable light-excited state. Furthermore, we examine an Fe3Cr-based single-molecule magnet, where light causes a change in the giant spin. We then progress to graphene nanoribbons, which offer an interesting semiconducting backbone for magnetic molecules. Through a comprehensive analysis of spin-spin couplings in nitronyl-nitroxide graphene nanoribbons, we eventually prove the existence of an edge state, which allows for two-qubit applications.