Photoisomerization of a Chiral Imine Molecular Switch Followed by Matrix-Isolation VCD Spectroscopy

Characterizing the stereochemistry of transient photoisomerization products remains a big challenge for the design of molecular machines, such as unidirectional molecular motors. Often these states are not stable long enough to be characterized in detail using conventional spectroscopic tools. The structurally simple camphorquinone imine 1 serves to illustrate the advantage of combining the matrix-isolation technique with vibrational circular dichroism (VCD) spectroscopy for the investigation of photoisomerizations of chiral molecules. In particular, it is shown that both (E)- and (Z)-1 can be generated photochemically at cryogenic temperatures in an argon matrix, and more importantly, that the stereochemistry of both switching states can be characterized reliably.