Photoswitching in a Molecular Cube

Switchable molecular materials are interesting both for future molecular electronics devices and for fundamental studies. Here we investigate the photoswitching in a Fe₄Co₄ molecular cube using X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). While in the ground state the molecule is diamagnetic, it can be promoted to the magnetic state by visible light. This excited state is stable at low temperatures, and the ground state can be recovered by heating up to room temperature. Our study shows that at the heart of the change in magnetism is a metal-to-metal charge transfer between pairs of Co and Fe ions triggered by light. This leads to a change in the oxidation states and to the presence of unpaired spins. In the XMCD experiment we investigate the element specific magnetic behavior, which contains information about the possible magnetic coupling between Co and Fe ions.