Molecular electronics is considered a promising approach for future nanoelectronic devices. In order that molecular junctions can be used as electrical switches or even memory devices, they need to be actuated between two distinct conductance states in a controlled and reproducible manner by external stimuli. Here we present a tripodal platform with a cantilever arm and a nitrile group at its end that is lifted from the surface. The formation of a coordinative bond between the nitrile nitrogen and the gold tip of a scanning tunnelling microscope can be controlled by both electrical and mechanical means, and leads to a hysteretic switching of the conductance of the junction by more than two orders of magnitude. This toggle switch can be actuated with high reproducibility so that the forces involved in the mechanical deformation of the molecular cantilever can be determined precisely with scanning tunnelling microscopy.

The efficient synthesis of tripodal platforms based on tetraphenylmethane with three acetyl-protected thiol groups in either meta or para positions relative to the central sp(3) carbon for deposition on Au (111) surfaces is reported. These platforms are intended to provide a vertical arrangement of the substituent in position 4 of the perpendicular phenyl ring and an electronic coupling to the gold substrate. The self-assembly features of both derivatives are analyzed on Au (111) surfaces by low-temperature ultra-high-vacuum STM, high-resolution X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, and reductive voltammetric desorption studies. These experiments indicated that the meta derivative forms a well-ordered monolayer, with most of the anchoring groups bound to the surface, whereas the para derivative forms a multilayer film with physically adsorbed adlayers on the chemisorbed para monolayer. Single-molecule conductance values for both tripodal platforms are obtained through an STM break junction experiment.

The efficient synthesis of a new tripodal platform based on a rigid 9,9'-spirobifluorene with three acetyl protected thiol groups in the positions 2, 3' and 6' for deposition on Au(111) surfaces is reported. The modular 9,9'-spirobifluorene platform provides both a vertical arrangement of the molecular rod in position 7 and its electronic coupling to the gold substrate. To demonstrate the validity of the molecular design, the model compound 24 exposing a para-cyanophenylethynyl rod is synthesized. Our synthetic approach is based on a metal-halogen exchange reaction of 2-iodobiphenyl derivative and his subsequent reaction with 2,7-disubstituted fluoren-9-one to afford the carbinol 16. Further electrophilic cyclization and separation of regioisomers provided the corresponding 2,7,3',6'-tetrasubstituted 9,9'-spirobifluorene 17 as the key intermediate. The molecular structure of 17 was determined by single-crystal X-ray diffraction crystallography. The self-assembly features of the target compound 24 were analyzed in preliminary UHV-STM experiments. These results already demonstrated the promising potential of the concept of the tripodal structure to stabilize the molecule on a Au(111) surface in order to control the spatial arrangement of the molecular rod.

We report on a cryogenic scanning tunneling microscope (STM) designed for single molecule studies, in which the light emitted from the tunneling junction is collected by an integrated optics on the tip. Using direct laser writing, the tip and the surrounding microscopic parabolic mirror are fabricated as one piece, which is small enough to collimate the collected light directly into an optical multimode fiber fixed inside the STM. This simple and compact setup combines high collection efficiency and ease of handling while not interfering with the cryostat operation, allowing uninterrupted measurements at 1.4 K for up to 5 days with low drift.

The tip of an STM induces transitions between six rotational states in tripodal sulfur-anchored stands with rotational axes.