A conjugated polymer nanowire can be created at any designated position in a monomolecular layer by initiating chain polymerization using a scanning tunneling microscope tip with a spatial precision of the order of 1 nm. The demonstration has been presented for a self-ordered monomolecular layer of 10,12-pentacosadiynoic acid, which is a diacetylene compound, adsorbed on a graphite surface. The polymer nanowires created have a length ranging from 5 to 300 nm, the length being controlled by domain boundaries or artificial defects in the molecular layer. The frequency of occurrence of chain polymerization is measured against the pulsed bias voltage, which suggests that the excitation of the molecule is caused by the inelastically tunneling electrons.

Single functional molecules offer great potential for the development of novel nanoelectronic devices with capabilities beyond today's silicon-based devices. To realise single-molecule electronics, the development of a viable method for connecting functional molecules to each other using single conductive polymer chains is required. The method of initiating chain polymerisation using the tip of a scanning tunnelling microscope (STM) is very useful for fabricating single conductive polymer chains at designated positions and thereby wiring single molecules. In this feature article, developments in the controlled chain polymerisation of diacetylene compounds and the properties of polydiacetylene chains are summarised. Recent studies of “chemical soldering”, a technique enabling the covalent connection of single polydiacetylene chains to single functional molecules, are also introduced. This represents a key step in advancing the development of single-molecule electronics.