The introduction of bulky substituents at the stereogenic center of light-driven second-generation molecular motors results in an acceleration of the speed of rotation. This is due to a more strained structure with elongated C=C bonds and a higher energy level of the ground state relative to the transition state for the rate-limiting thermal isomerization step. Understanding the profound influence that variation of the substituent at the stereogenic center holds over the rotational speed of the light-driven molecular motor has enabled the development of the fastest molecular motor reported thus far.
Department of Organic and Molecular Inorganic Chemistry, Stratingh Institute, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, The Netherlands.
