Nanographene-based host–guest systems

The electronic structure of nanographene depends on the shape of their edges. Around the zigzag-shaped edges, nonbonding edge state of π-electron origin is created, which is the origin of electronic and chemical activities of nanographene. In addition, the strongly spin polarized edge state has localized spin, giving magnetic activity to nanographene. We investigate the magnetic properties of nanoporous activated carbon fibers consisting of a three dimensional disordered network of nanographite domains, each of which is a stack of 3–4 nanographene sheets, in relation to host–guest interaction. Chemically inert guest species such as water, organic solvent, argon physisorbed into the nanopores mechanically compress the nanographite domains, resulting in a high spin/low spin magnetic switching phenomenon induced by the physisorption. The presence of an energy gap and the nanographene edges decorated by oxygen-containing functional groups make nanographene less amphoteric, modifying charge transfer mechanism in the host–guest interaction. HNO3 shows a two-step charge transfer process. In the Br adsorption, physisorbed Br species cooperate with charge transfer Br species, giving an interesting interplay of charge transfer and magnetic switching. In the K adsorption, physisorbed K atoms form antiferromagnetic K clusters in the nanopores, while a part of K species is responsible for charge transfer.

► Unconventional features of host–guest interaction in semi-amphoteric nanographene.
► Mechanical compression induced magnetic switching phenomenon.
► Antiferromagnetic potassium clusters in nanographene-based nanoporous carbon.