Nanomechanical function made possible by suppressing structural transformations of polyarylacetylenes

Self-assembling dendrons sterically disfavor the cisoid conformation through which 6 pi-electrocyclization proceeds in cis-polyarylacetylenes. Through the same mechanism, selected self-organizable dendronized helical cis-polyphenylacetylenes (cis-PPAs) undergo an unprecedented thermally induced cisoid-to-transoid conformational isomerism in bulk. The motion of helix (un)winding can be converted to unidirectional motion in self-organizable den-dronized cis-PPAs. By eliminating 6 pi-electrocyclization, nanomechanical actuators capable of lifting a US dime have been prepared from self-organizable dendronized cis-PPAs.