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

A series of <i>N</i>²,<i>N</i>⁶-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>₂ 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

Molecular Turnstiles Regulated by Metal Ions

A family of novel molecular turnstiles <b>1</b>–<b>3</b> composed of two stators with pyridyl binding sites and a different-sized triptycene rotor was synthesized. The molecular turnstiles behave in an open state at room temperature in the absence of metal ions but display significantly different closed states in the presence of Ag⁺ and Pd²⁺. The Ag⁺-mediated turnstiles <b>1</b>–<b>3Ag</b> exhibited closed states but unreadable bistability at ambient temperature because the Ag⁺-mediated macrocyclic framework is not able to restrict the rotations of the rotors; while temperature was decreased, the macrocyclic frameworks became stable enough to halt the rotations of the rotors, eventually leading to the readable closed states for <b>1</b>–<b>3Ag</b>. In contrast, Pd²⁺-mediated macrocyclic frameworks are stable, giving rise to a detectable closed state of turnstiles <b>1</b>–<b>3Pd</b> in a wide range of temperatures. These findings have also been supported by DFT calculations

Molecular Turnstiles Regulated by Metal Ions

A family of novel molecular turnstiles <b>1</b>–<b>3</b> composed of two stators with pyridyl binding sites and a different-sized triptycene rotor was synthesized. The molecular turnstiles behave in an open state at room temperature in the absence of metal ions but display significantly different closed states in the presence of Ag⁺ and Pd²⁺. The Ag⁺-mediated turnstiles <b>1</b>–<b>3Ag</b> exhibited closed states but unreadable bistability at ambient temperature because the Ag⁺-mediated macrocyclic framework is not able to restrict the rotations of the rotors; while temperature was decreased, the macrocyclic frameworks became stable enough to halt the rotations of the rotors, eventually leading to the readable closed states for <b>1</b>–<b>3Ag</b>. In contrast, Pd²⁺-mediated macrocyclic frameworks are stable, giving rise to a detectable closed state of turnstiles <b>1</b>–<b>3Pd</b> in a wide range of temperatures. These findings have also been supported by DFT calculations