A Rotation-Inversion Dual-Motion Molecular Switch: Race for NMR Signaling.

The interplay between the thermal helical inversion (THI) of the stiff -stilbene moiety and the rotation of the dimethylamino (DMA) group in 1 results in a dependence of the DMA NMR signals on the THI kinetics in ( E )- 1 but the rotation kinetics in ( Z )- 1 , because the faster motion mode is responsible. Consequently, the photochemical switching from ( E )- 1 to ( Z )- 1 illustrates the phenomenon of "switchable motion detection" by the same set of NMR signals in a dual-motion molecular system.