Chiroptical Inversion Induced by Rotation of a Carbon–Carbon Single Bond: An Experimental and Theoretical Study

We propose a new strategy to construct chiral molecular switches with highly reversible and sensitive chiroptical responses to variations in the external environment. Its fundamental concept involves a stimuli-triggered exchange of two conformations presenting significantly different chiroptical properties through the rotation of a carbon–carbon single bond, as demonstrated by chiral Schiff bases <i>s</i>-<b>1</b>, <i>s</i>-<b>2</b>, and a salicylamide analogue <i>s</i>-<b>3</b>. Upon addition of base in solution, the circular dichroism (CD) spectra of these molecular switches displayed unique changes featuring an inversion of the Cotton effect’s signs, and the original CD profiles can be recoverd by acidification. Various spectroscopic studies as well as the conformational analysis combining with TDDFT computations allowed clear elucidation of the chiroptical inversion mechanism. It is expected that this kind of chiroptical switches is of great interest for molecular recognition, chemosensing, and the construction of molecular-scale devices. Furthermore, the present study indicates that the use of the conformational transition about a single bond may serve as the basis for designing chiroptical inversion systems.