2,6-Pyridodicarboxamide-Bridged Triptycene Molecular Transmission Devices: Converting Rotation to Rocking Vibration

A series of N(2),N(6)-bis(triptycene-9-yl)pyridine-2,6-dicarboxamides 1-4 were designed and synthesized. Due to rotational constraint of the 2,6-diamidopyridine bridge, the triptycene components in the systems are held together. X-ray structures of 1-4 show that the molecules adopt a gear-like geometry in the solid states. DFT (B3LYP/6-31G(d)) calculations predict the gear-like C2 conformation as global minimum structures for 1 and 2 and suggest that, through a slippage transition process, rotation of one triptycene component would give rise to a rocking vibration of the counter component due to the barrier for rotation of the triptycene components. VT NMR studies on 1-4 show that the pair of triptycene components undergo ceaseless slippage at room temperature but nearly freeze at temperatures as low as 183 K. Decreasing the temperature freezes the slippage between triptycene components as well, thus producing the appearance of phase isomers of 3 and 4. The dynamic features of the studied molecules indicate that this kind of molecule is able to function as a kind of molecular transmission device for transforming the mode of motion from rotation to rocking vibration.