Topology Dictates Magnetic and Conductive Properties of a π-Stacked System: Insight into Possible Coexistence of Magnetic and Conductive Systems

In this paper, conductivity and magnetism in alternant hydrocarbons are discussed based on the topology of π-conjugated networks. In a molecular system with two spin centers, when the spins are separated by an odd-length walk, they interact antiferromagnetically with each other, but when they are separated by an even-length walk, they interact ferromagnetically. The conduction through the pathway connecting the two spins is expected to be effective for the former case, while ineffective for the latter case, but both show almost the same conductance in a magnetic system. This is because in the latter case, a feature in the electron transmission spectrum that causes destructive quantum interference is localized away from the Fermi level of the electrode and in a very narrow energy range, not affecting the zero-bias conductance. This tendency is further accentuated by generating weak coupling between the electrode surfaces and the spins to preserve the radical character of the molecule sandwiched between two electrodes. Although there is a challenge on how to stabilize radical molecules in a confined environment between electrodes, what is presented in this paper would give a clue on how to construct a system where magnetism and conductivity coexist.