Fullerene-Based Switching Molecular Diodes Controlled by Oriented External Electric Fields.

Employing multiscale in silico modeling, we propose switching molecular diodes on the basis of endohedral fullerenes (fullerene switching diode, FSD), encapsulated with polar molecules of general type MX (M: metal, X: nonmetal) to be used for data storage and processing. Here, we demonstrate for MX@C70 systems that the relative orientation of enclosed MX with respect to a set of electrodes connected to the system can be controlled by application of oriented external electric field(s). We suggest systems with two- and four-terminal electrodes, in which the source and drain electrodes help the current to pass through the device and help the switching between the conductive states of FSD via applied voltage. The gate electrodes then assist the switching by effectively lowering the energy barrier between local minima via stabilizing the transition state of switching process if the applied voltage between the source and drain is insufficient to switch the MX inside the fullerene. Using nonequilibrium Green's function combined with density functional theory (DFT-NEGF) computations, we further show that conductivity of the studied MX@C70 systems depends on the relative orientation of MX inside the cage with respect to the electrodes. Therefore, the orientation of the MX inside C70 can be both enforced ("written") and retrieved ("read") by applied voltage. The studied systems thus behave like voltage-sensitive switching molecular diodes, which is reminiscent of a molecular memristor.

How Does a Container Affect Acidity of its Content: Charge-Depletion Bonding Inside Fullerenes.

A recent study (Sci. Adv. 2017, 3, e1602833) has shown that FH⋅⋅⋅OH2 hydrogen bond in a HF⋅H2 O pair substantially shortens, and the H-F bond elongates upon encapsulation of the cluster in C70 fullerene. This has been attributed to compression of the HF⋅H2 O pair inside the cavity of C70 . Herein, we present theoretical evidence that the effect is not caused by a mere compression of the H2 O⋅HF pair, but it is related to a strong lone-pair-π (LP-π) bonding with the fullerene cage. To support this argument, a systematic electronic structure study of selected small molecules (HF, H2 O, and NH3 ) and their pairs enclosed in fullerene cages (C60 , C70 , and C90 ) has been performed. Bonding analysis revealed unique LP-πcage interactions with a charge-depletion character in the bonding region, unlike usual LP-π bonds. The LP-πcage interactions were found to be responsible for elongation of the H-F bond. Thus, the HF appears to be more acidic inside the cage. The shortening of the FH⋅⋅⋅OH2 contact in (HF⋅H2 O)@C70 originates from an increased acidity of the HF inside the fullerenes. Such trends were also observed in other studied systems.