The field of molecular electronics aims at advancing the miniaturization of electronic devices, by exploiting single molecules to perform the function of individual components. A molecular switch is defined as a molecule that displays stability in two or more states (e.g. “on” and “off” involving conductance, conformation etc.) and upon application of a controlled external perturbation, electric or otherwise, undergoes a reversible change such that the molecule is altered. Previous work has shown multi-state molecular switches with up to four and six distinct states. Using low temperature scanning tunnelling microscopy and spectroscopy, we report on a multi-state single molecule switch using the endohedral fullerene Li@C 60 that displays 14 molecular states which can be statistically accessed. We suggest a switching mechanism that relies on resonant tunnelling via the superatom molecular orbitals (SAMOs) of the fullerene cage as a means of Li activation, thereby bypassing the typical vibronic excitation of the carbon cage that is known to cause molecular decomposition.

Angle-resolved photoelectron spectroscopy and scanning tunnelling spectroscopy studies of the endohedral fullerene Li@C 60 .Gas phase photoelectron spectroscopy, TD-DFT calculations and low temperature UHV STM experiments are combined to provide information about the infl uence of the encapsulated Li on the symmetry and energetics of the low lying diff use Super-Atom Molecular Orbitals (SAMOs) of Li@C 60 . PAPER Yao Cai, Yongxin Pan et al. Positive magnetic resonance angiography using ultrafi ne ferritin-based iron oxide nanoparticles Nanoscale rsc.li/nanoscale Volume Gas phase photoelectron spectroscopy (Rydberg Fingerprint Spectroscopy), TDDFT calculations and low temperature STM studies are combined to provide detailed information on the properties of the diffuse, low-lying Rydberg-like SAMO states of isolated Li@C 60 endohedral fullerenes. The presence of the encapsulated Li is shown by the calculations to produce a significant distortion of the lowest-lying S-and P-SAMOs that is dependent on the position of the Li inside the fullerene cage. Under the high temperature conditions of the gas phase experiments, the Li is mobile and able to access different positionswithin the cage. This is accounted for in the comparison with theory that shows a very good agreement of the photoelectron angular distributions, allowing the symmetry of the observed SAMO states to be identified. When adsorbed on a metal substrate at low temperature, a strong interaction between the lowlying SAMOs and the metal substrate moves these states to energies much closer to the Fermi energy compared to the situation for empty C 60 while the Li remains frozen in an off-centre position. † Electronic supplementary information (ESI) available: Temperature-dependent mass spectrometry, laser power ionisation dependence and STM imaging details.

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