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首页> 外文期刊>Chemistry: A European journal >Ground-state equilibrium thermodynamics and switching kinetics of bistable [2]rotaxanes switched in solution, polymer gels, and molecular electronic devices
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Ground-state equilibrium thermodynamics and switching kinetics of bistable [2]rotaxanes switched in solution, polymer gels, and molecular electronic devices

机译：在溶液，聚合物凝胶和分子电子器件中转换的双稳态[2]轮烷的基态平衡热力学和转换动力学

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We report on the kinetics and ground-state thermodynamics associated with electrochemically driven molecular mechanical switching of three bistable [2]rotaxanes in acetonitrile solution, polymer electrolyte gels, and molecular-switch tunnel junctions (MSTJs). For all rotaxanes a it-electron-deficient cyclobis(paraquat-p-phenylene) (CBPQT(4+)) ring component encircles one of two recognition sites within a dumbbell component. Two rotaxanes (RATTF(4+) and RTTF4+) contain tetrathiafulvalene (TTF) and 1,5-dioxynaphthalene (DNP) recognition units, but different hydrophilic stoppers. For these rotaxanes, the CBPQT(4+) ring encircles predominantly (> 90 %) the TTF unit at equilibrium, and this equilibrium is relatively temperature independent. In the third rotaxane (RBPTTF4+), the TTF unit is replaced by a pi-extended analogue (a bispyrrolotetrathiafulvalene (BPTTF) unit), and the CBPQT(4+) ring encircles almost equally both recognition sites at equilibrium. This equilibrium exhibits strong temperature dependence. These thermodynamic differences were rationalized by reference to binding constants obtained by isothermal titration calorimetry for the complexation of model guests by the CBPQT(4+) host in acetonitrile. For all bistable rotaxanes, oxidation of the TTF (BPTTF) unit is accompanied by movement of the CBPQT(4+) ring to the DNP site. Reduction back to TTF0 (BPTTF0) is followed by relaxation to the equilibrium distribution of translational isomers. The relaxation kinetics are strongly environmentally dependent, yet consistent with a single electromechanical-switching mechanism in acetonitrile, polymer electrolyte gels, and MSTJs. The ground-state equilibrium properties of all three bistable [2]rotaxanes were reflective of molecular structure in all environments. These results provide direct evidence for the control by molecular structure of the electronic properties exhibited by the MSTJs.
机译：我们报告了与乙腈溶液，聚合物电解质凝胶和分子开关隧道结（MSTJs）中的三种双稳态[2]轮烷的电化学驱动分子机械转换相关的动力学和基态热力学。对于所有轮烷，它都缺乏电子，环双（百草枯-对亚苯基）（CBPQT（4+））环成分环绕哑铃成分内的两个识别位点之一。两个轮烷（RATTF（4+）和RTTF4 +）包含四硫富瓦烯（TTF）和1,5-二氧萘（DNP）识别单元，但具有不同的亲水性塞子。对于这些轮烷，CBPQT（4+）环在平衡状态下主要围绕（> 90％）TTF单元，并且该平衡状态与温度无关。在第三个轮烷中（RBPTTF4 +），TTF单元被pi扩展类似物（双吡咯并四硫富瓦烯（BPTTF）单元）取代，CBPQT（4+）环几乎相等地包围两个识别位点。这种平衡表现出强烈的温度依赖性。通过参考等温滴定量热法获得的结合常数，将CBPQT（4+）主体在乙腈中络合，从而获得了这些热力学差异。对于所有双稳态轮烷，TTF（BPTTF）单元的氧化伴随着CBPQT（4+）环向DNP位点的移动。还原回到TTF0（BPTTF0）之后，放松至翻译异构体的平衡分布。弛豫动力学在很大程度上取决于环境，但与乙腈，聚合物电解质凝胶和MSTJ中的单个机电转换机制一致。所有三种双稳态[2]轮烷的基态平衡性质都反映了在所有环境中的分子结构。这些结果为通过分子结构控制由MSTJ表现出的电子性质提供了直接的证据。

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