For the development of electronics down to atomic scale, it is of fundamental importance to build devices and atomic-size interconnections in a planar geometry and to be able to controllably switch between different connection paths. Molecular wires, molecular switches and atomic circuits are therefore intensively investigated. In this talk, recent results will be reviewed, where molecularwires and switches are studied by scanning tunneling microscope (STM)at low temperature on metallic and semiconducting surfaces.  Acene chains are molecular wires that present an extended rigid, planar and fully π-conjugated backbone. Larger acenes are expected to show superior electronic properties with increasing radical character.

However, their limited stability under ambient conditions has hampered their application so far. Here, I will discuss the electronic properties of hexacene and smaller acenes, that we directly synthetized on Au(111).  Dangling bond wires on H:Si(100) provides an alternative to molecules for building electronic devices at the atomic scale. In such dangling bond quantum circuits, molecular switches are necessary to provide the logical input. I will show that acetylbiphenyl molecules adsorbed on Si(100) can be electronically switched between two stable conformations, passivating and de-passivating a dangling-bond pair.  Finally, mechanical molecular systems can provide an alternative route to transmit information at the nanoscale and could compete, in terms of high-clock frequency and robustness to radiations, with electronic, optical and magnetic devices. In the last part of this talk, I will discuss recent results and perspectives for the transmission of motion between molecules, towards the construction of single molecule-machines.