Neumann Mathias S, Jensen Sofie K, Frederiksen Rikke, Andersen Sissel S, Beck Kasper M, Jeppesen Jan O
Department of Physics, Chemistry, and Pharmacy, University of Southern Denmark, Campusvej 55, Odense M, 5230, Denmark.
Chempluschem. 2025 Jun;90(6):e202500154. doi: 10.1002/cplu.202500154. Epub 2025 Apr 9.
Control of movement in artificial molecular machines relies on the formation of out-of-equilibrium states that can subsequently interconvert to their ground states. However, a detailed description of molecular machines that are out of equilibrium is a challenge because they are often too short-lived to be characterized. Herein, the synthesis of two cyclobis(paraquat-p-phenylene) [2]rotaxanes that incorporate a redox-active monopyrrolotetrathiafulvalene unit as the primary station and either a hydroquinone or a xylyl moiety as the secondary station is described. It is shown that the bistable [2]rotaxanes can be pushed out of equilibrium by an oxidation/reduction cycle and since a steric barrier is located between the two stations, the out-of-equilibrium states of the [2]rotaxanes can be physically isolated as solids. This allows to make detailed spectroscopic and electrochemical investigations of the [2]rotaxanes in both the di-oxidized and un-oxidized states. The outcome of the studies shows that the replacement of the secondary hydroquinone station with a xylyl station has no impact on the thermodynamic properties but has a significant effect on the kinetic properties of the [2]rotaxanes illustrating that the nature of the secondary station can be used to control the speed of [2]rotaxane-based molecular machines.
人工分子机器中的运动控制依赖于非平衡态的形成，这些非平衡态随后可相互转化为基态。然而，对处于非平衡态的分子机器进行详细描述是一项挑战，因为它们往往寿命太短，难以进行表征。本文描述了两种环双（百草枯 - 对亚苯基）[2]轮烷的合成，它们包含一个氧化还原活性的单吡咯并四硫富瓦烯单元作为主要站点，以及一个对苯二酚或一个二甲苯基部分作为次要站点。结果表明，双稳态[2]轮烷可以通过氧化/还原循环被推离平衡态，并且由于两个站点之间存在空间位垒，[2]轮烷的非平衡态可以作为固体被物理隔离。这使得能够对处于二氧化态和未氧化态的[2]轮烷进行详细的光谱和电化学研究。研究结果表明，用二甲苯基站点取代次要的对苯二酚站点对热力学性质没有影响，但对[2]轮烷的动力学性质有显著影响，这说明次要站点的性质可用于控制基于[2]轮烷的分子机器的速度。
