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

A series of N2,N6-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.

本研究设计并合成了一系列N²,N⁶-二(三蝶烯-9-基)吡啶-2,6-二甲酰胺类化合物1~4。由于2,6-二酰胺吡啶桥连结构的旋转受限效应，体系中的三蝶烯单元被固定排布。化合物1~4的X射线晶体结构表明，固态下该类分子呈现类齿轮状几何构型。密度泛函理论（DFT，B3LYP/6-31G(d)）计算结果显示，化合物1和2的全局最低能量构型为类齿轮状的C₂对称构象；计算同时表明，由于三蝶烯单元存在旋转能垒，通过滑移过渡过程，单个三蝶烯单元的旋转将引发对应单元的摇摆振动。变温核磁共振（VT NMR）对1~4的研究结果显示，室温下一对三蝶烯单元会持续发生滑移，但在低至183 K的温度下滑移几乎被冻结。随着温度降低，三蝶烯单元间的滑移同样被冻结，由此使化合物3和4表现出相异构体特征。所研究分子的动态特性表明，该类分子可作为一类分子传动装置，实现运动模式从旋转到摇摆振动的转换。