Controlling the Conformation of 2-Dimethylaminobiphenyls by Transient Intramolecular Hydrogen Bonding.

Temporal control of molecular motions is receiving increasing attention because it is central to the development of molecular switches and motors and nanoscopic materials with life-like properties. Inspired by previous studies, here, we report that acid can be used to temporally control the conformational freedom around the C-C bond connecting the two aromatic rings of the ditopic bases and . Consistent with NMR measurements and DFT calculations, before fuel addition, the conformational motion of the two aromatic rings of both and mainly consists of a large amplitude torsional oscillation spanning about 260° and passing for the conformation (the two nitrogen atoms at opposite sides). Immediately after the addition of , due to the protonation of one nitrogen and consequent formation of an N-H···N intramolecular hydrogen bond, the torsional oscillation in both H and H is not only restricted to a smaller range (about 100°) but explores the previously forbidden conformational space around the conformation (the two nitrogen atoms at the same side). However, the new state is an out-of-equilibrium state since decarboxylation of the conjugate base of takes place and, at the end of the process, the system reverts to the more conformationally mobile state.