A ferrocene based switchable molecular folding ruler.

A 2,2'-bipyridine-appended bis(ferrocene) three tiered molecular folding ruler, can be switched from a folded conformation to an extended conformation by the addition of [Cu(CH3 CN)4 ](PF6 ) and 6,6'-dimesityl-2,2'-bipyridine. This extension and contraction process could be triggered either chemically or electrochemically and was reversible.