With the hope of directing future bottom-up fabrication through bulk external stimuli (such as electric fields) on nanometer-sized transporters, we sought to study controlled molecular motion on surfaces through the rational design of surface-capable molecular structures called nanocars. Here we show that the observed movement of the nanocars is a new type of fullerene-based wheel-like rolling motion, not stick-slip or sliding translation, due to evidence including directional preference in both direct and indirect manipulation and studies of related molecular structures.

Design, syntheses, and testing of new, fullerene-wheeled single molecular nanomachines, namely, nanocars and nanotrucks, are presented. These nanovehicles are composed of three basic components that include spherical fullerene wheels, freely rotating alkynyl axles, and a molecular chassis. The use of spherical wheels based on C60 and freely rotating axles based on alkynes permits directed nanoscale rolling of the molecular structure on gold surfaces. The rolling motion observed by STM resembles the same motion performed by macroscopic entities in which rolling occurs perpendicular to the axles. A new synthesis methodology, in situ ethynylation of fullerenes, was developed for the realization of the fullerene-wheeled molecular machines. Four generations of the fullerene-wheeled structures were developed, and the latest fourth generation nanocar, 3b, along with three-wheeled triangular compounds, 4a and 4b, provided definitive evidence for fullerene-based wheel-like rolling motion, not stick-slip or sliding translation. The studies here underscore the ability to control directionality of motion in molecular-sized nanostructures through precise molecular design and synthesis.

Nanocars with an angled chassis have been synthesized and imaged using scanning tunneling microscopy. These angled chassis nanocars were designed to further our understanding of the directional control and surface-rolling capabilities of this class of nanomachines. The alkylated carbazole inner core might enable the molecular scaffold to produce circular rolling motions of the nanovehicles on surfaces.

To build up true molecular machines and understand the mechanics of nanoscale motion and manipulation in molecular system, we have created and investigated a family of molecules based around the concept of the nanocar, which has the rolling wheels made of spherical fullerene or carborane molecules. Assisted by scanning tunneling microscopy (STM), we have successfully characterized and manipulated these molecules. In addition, we have observed the behavior of these systems when thermal energy is applied. These initial studies open a new realm of nano-sized mechanical, chemical, and electrical devices.