2,6-Pyridodicarboxamide-Bridged
Triptycene Molecular
Transmission Devices: Converting Rotation to Rocking Vibration
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Abstract
A series of <i>N</i><sup>2</sup>,<i>N</i><sup>6</sup>-bis(triptycene-9-yl)pyridine-2,6-dicarboxamides <b>1</b>–<b>4</b> 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 <b>1</b>–<b>4</b> show that the molecules adopt a gear-like
geometry in the solid states. DFT (B3LYP/6-31G(d)) calculations predict
the gear-like <i>C</i><sub>2</sub> conformation as global
minimum structures for <b>1</b> and <b>2</b> 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 <b>1</b>–<b>4</b> 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 <b>3</b> and <b>4</b>. 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
