Spin probe for dynamics of the internal cluster in endohedral metallofullerenes

Endohedral metallofullerenes (EMFs) are constructed by fullerene cages encapsulating various metal atoms or metal clusters, which usually exhibit some motion. However, due to the fact that the elusive endohedral dynamics are related to many factors, it remains a challenge to image the motion of internal species. Recently, the electron spin was found to be a sensitive probe to detect the motion of internal species in EMFs. Moreover, this technique can be widely applied for many metallofullerenes, i.e., for paramagnetic EMFs, the unpaired electron spin is a natural probe for the endohedral dynamics, and for diamagnetic EMFs, an electron can be introduced to produce spin-active EMF molecules. Based on the analysis of hyperfine coupling constants (hfcc), g-factors, and line patterns of the ESR spectra of EMFs, the spin centers and endohedral dynamics can be deduced. It has been revealed that the spin probes can provide unexpected information about the dynamics of the internal clusters in EMFs. Through changing the temperature, exohedral modification of the EMF, and supramolecular assembly, the motion of the internal species in EMFs can be manipulated, as clearly reflected by the spin probe. These studies revealed that the spin in EMFs exhibits promising applications in quantum sensing and molecular machine technology. In this review, we will address the use of the spin probe in EMFs and attempt to understand the effects in the detection of the endohedral dynamics.