Previously Described Synthetic Systems based on Purely Organic Components

Previously Described Synthetic Systems based on Purely Organic Components 

Photochemistry offers many examples of large-scale movement at the molecular level. The cis-trans isomerization127-33- of an azo group is a very attractive process for modification of the geometry and the properties of compounds, although several other photochemical reactions can be utilized,134-371 including the photoisomerization of stilbene-like compounds. 

A chemical signal can also be used, as in the recently described molecular brake .1381 In this case, rather than its shape, it is more the motion dynamic properties of the compound (rotation of a group about a C-C bond) that are modified, by addition of a transition metal. 

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