On–off switching of the correlated motion in a rotation‐inversion dual‐mode molecular system

• Published in: Journal of the Chinese Chemical Society (Taipei) Vol. 69; no. 8; pp. 1475 - 1484
• Main Authors: Chen, Zi‐Jian, Lu, Hsiu‐Feng, Chao, Ito, Yang, Jye‐Shane
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley‐VCH Verlag GmbH & Co. KGaA 01.08.2022; Wiley Subscription Services, Inc
• Subjects: Correlation; Isomerization; molecular device; Molecular machines; NMR; Nuclear magnetic resonance; organic chemistry; Protons; Rotation; spectroscopy; Stilbene; Switches; theoretical molecular science
• ISSN: 0009-4536; 2192-6549
• DOI: 10.1002/jccs.202200190

We report herein a new rotation‐inversion dual‐motion molecular switch (1), in which a 3,3‐dimethylazetidinyl (DMAZ) group is the rotator and a stiff‐stilbene is the helical stator. There are two sets of nuclear magnetic resonance (NMR) signals in the DMAZ group, the H‐shaped AZ protons and the planar C2‐symmetrical Me protons, for probing the kinetics of the DMAZ rotation and the stiff‐stilbene inversion. While the two motion modes are highly correlated in (E)‐1, they are decoupled in (Z)‐1. The rotation‐inversion correlated motion in (E)‐1 is governed by the faster inversion mode, whereas the inversion is much slower than the rotation in (Z)‐1. Consequently, photochemical isomerization between (E)‐1 and (Z)‐1 switches not only the relative rate of the rotation versus inversion motion but also the on–off behavior of the rotation‐inversion correlated motion. This work shows the cooperation of two sets of proton signals in elucidating the correlated motion in a dual‐motion molecular system. The dimethylazetidinyl rotator, which contains both the H‐shaped and the C2‐planar NMR proton signals, in 1 is able to probe the rotation‐inversion correlated motion in (E)‐1 and the independent rotation kinetics in (Z)‐1.