A fullerene molecular tip can detect localized and rectified electron tunneling within a single fullerene–porphyrin pair

Abstract

A fullerene molecular tip was used to detect electron tunneling from a single porphyrin molecule. Electron tunneling was found to occur locally from an electron-donating moiety of the porphyrin to the fullerene through charge-transfer interaction between them. In addition, electron tunneling within the single fullereneporphyrin pair exhibited rectifying behavior in which electrons can be driven only at the direction from the porphyrin to the fullerene. It is demonstrated that localized electron tunneling enables us to spatially visualize the frontier orbital of the porphyrin involved in electron tunneling. In addition, rectification demonstrates that the fullerene-porphyrin pair constitutes a molecular rectifier. We believe that molecular tips bring insight into intermolecular electron transmission toward realization of molecular electronics as shown here. molecular electronics ͉ nanoscience ͉ scanning tunneling microscopy E lectron transmission through single molecules is currently an interdisciplinary subject of substantial interest (1) because of molecular-scale electronic device research (2, 3). It is desired to measure the molecular conduction on a single molecule rather than on an ensemble of molecules to eliminate a cooperative transport (4) and avoid averaging out the conduction through the molecules in different conformations (5). Recently, there have been significant advances in knowledge of electron transmission through a single molecule (4). However, few works have been reported on electron transmission through a single molecule to an adjacent single molecule on a nanoscale.Scanning tunneling microscopy (STM) has been an essential tool in nanosciences (6). We have studied the construction of molecular tips for STM. The molecular tip is prepared by chemical modification of an underlying metal tip, and the outermost single adsorbate probes electron tunneling to or from a sample molecule. Importantly, the tunneling current increases when sample and tip molecules form metal coordination or hydrogen-bond interactions that provide overlap of their electronic wave functions. The current increase is ascribed to facilitated tunneling through overlapped wave functions. We have demonstrated that this phenomenon can be used for selective observation of chemical species to overcome poor chemical selectivity in conventional STM (7-13). Because the overlap of electronic wave functions is important for the facilitation of electron tunneling, these results suggest that intermolecular electron tunneling can also be facilitated through a charge-transfer interaction as well as metal coordination and hydrogen-bond interactions.Here, we report on the detection of intermolecular electron tunneling within a single fullerene-porphyrin molecular pair. Electron tunneling was found to occur locally from an electrondonating moiety of the porphyrin to the fullerene through charge-transfer interaction between them, but not in the opposite direction. It was shown that localized tunneling can be applied to visualize the frontier orb...

Interactions between two C60molecules measured by scanning probe microscopies

“…As a result, the short-range force around the point of maximal attraction could be determined as a function of the intermolecular distance. Owing to their rigidity C 60 tips may also be used for lateral scanning [1,[16][17][18]. This enables measurements in the distance range near mechanical contact that extend the previous one-dimensional measurements to the lateral dimensions.…”

Molecular Tips for Scanning Tunneling Microscopy: Intermolecular Electron Tunneling for Single-molecule Recognition and Electronics

“…Thus, it was concluded that the C60 tip allows the quantification of electron transfer in a single fullerene-porphyrin assembly linked via the chargetransfer interaction. We previously demonstrated the rectification property of a porphyrin-fullerene pair, 9 which renders the molecular assembly particularly attractive in molecular electronics. The I-z measurement using the C60 tip was successfully applied to the quantitative evaluation of the rectification for a single porphyrin-fullerene assembly.…”

“…In molecular electronics, individual molecules or a small group of molecules are utilized as electronic components, such as wires, 6,7 diodes, [8][9][10] switches, 11,12 and transistors, 13,14 to perform certain electronic functions. 15 Therefore, the most fundamental question in this field is what is the electronic conductance of a junction composed of a single (or a few) molecule(s).…”

“…Therefore, it was concluded that electron tunneling through charge-transfer interactions can spatially visualize the frontier orbitals involved in the interactions. 9 In addition to the charge-transfer interaction, hydrogen-bond and coordination-bond interactions between the sample and the tip molecules can be used to achieve chemically selective imaging.…”

“…These studies have been motivated by increasing interest in molecular electronics, which utilizes an individual molecule or a small group of molecules as an electronic component to perform certain functions. A large number of molecules with unique electronic functions, e.g., wires, 6,7 diodes, [8][9][10] switches, 11,12 and transistors, 13,14 have been reported. 15 We have developed molecular tips for STM.…”