Speaker
Description
Imine-based molecular switches were recently developed, and so their properties remain largely unexplored[1]. Their potential to perform multi-step unidirectional rotations make them an important addition to the existing nanomotor toolbox[2]. Microwave rotational spectroscopy allows us to study the 3D structure of these molecules with great precision since we can relate the pattern of rotational frequencies to the structure through the moments of inertia. The different energies of the various conformations means that, when in equilibrium, they exist with a given distribution. In solution, the interactions between the solvent molecules and the solute can alter the energetic balance of the conformers[3]. In this contribution we present a rotational study of a chiral camphorquinone imine. From our investigations we uncovered the structure of the open (E) and closed (Z) configurations of the switch and their first and second order microsolvated species, which were validated using experimental isotopic information. The predicted favoured stability of Z over E in the gas phase is experimentally shown to reverse in the presence of water, with increasing abundance of E over Z with increasing cluster size. In an attempt to understand the origin of this reversal, we used quantum chemistry calculations to interpret the observed change in stability for isolated versus solvated scenarios. We will discuss our findings and the suitability of rotational spectroscopy to engage in structural studies of highly functional micro-solvated molecular systems.
References:
[1] L. Greb, A. Eichhöfer, J.-M. Lehn, Angew. Chem. Int. Ed., 2015, 54, 14345-14348
[2] S. Kassem, T. van Leeuwen, A. S. Lubbe, M. R. Wilson, B. L. Feringa, D. A. Leigh, Chem. Soc. Rev., 2017, 46, 2592-2621
[3] C. H. Pollok, T. Riesebeck, C. Merten, Angew. Chem. Int. Ed., 2017, 56, 1925-1928
