Choi Jang Wook, Flood Amar H, Steuerman David W, Nygaard Sune, Braunschweig Adam B, Moonen Nicolle N P, Laursen Bo W, Luo Yi, DeIonno Erica, Peters Andrea J, Jeppesen Jan O, Xu Ke, Stoddart J Fraser, Heath James R
Division of Chemistry and Chemical Engineering (127-72), California Institute of Technology, 1200 E. California Blvd. Pasadena, CA 91125, USA.
Chemistry. 2005 Dec 16;12(1):261-79. doi: 10.1002/chem.200500934.
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 pi-electron-deficient cyclobis(paraquat-p-phenylene) (CBPQT4+) ring component encircles one of two recognition sites within a dumbbell component. Two rotaxanes (RATTF4+ and RTTF4+) contain tetrathiafulvalene (TTF) and 1,5-dioxynaphthalene (DNP) recognition units, but different hydrophilic stoppers. For these rotaxanes, the CBPQT4+ 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 CBPQT4+ 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 CBPQT4+ host in acetonitrile. For all bistable rotaxanes, oxidation of the TTF (BPTTF) unit is accompanied by movement of the CBPQT4+ 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.
我们报告了与三种双稳态[2]轮烷在乙腈溶液、聚合物电解质凝胶和分子开关隧道结（MSTJ）中电化学驱动的分子机械开关相关的动力学和基态热力学。对于所有轮烷，一个缺π电子的环双（百草枯 - 对亚苯基）（CBPQT4 +）环组分环绕着哑铃状组分内的两个识别位点之一。两个轮烷（RATTF4 +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封端基团。对于这些轮烷，CBPQT4 +环在平衡时主要（> 90％）环绕TTF单元，并且该平衡相对与温度无关。在第三个轮烷（RBPTTF4 +）中，TTF单元被一个π扩展类似物（双吡咯并四硫富瓦烯（BPTTF）单元）取代，并且CBPQT4 +环在平衡时几乎同等程度地环绕两个识别位点。该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CBPQT4 +主体在乙腈中与模型客体络合的结合常数，对这些热力学差异进行了合理化解释。对于所有双稳态轮烷，TTF（BPTTF）单元的氧化伴随着CBPQT4 +环向DNP位点的移动。还原回TTF0（BPTTF0）后接着松弛到平移异构体的平衡分布。松弛动力学强烈依赖于环境，但与乙腈、聚合物电解质凝胶和MSTJ中的单一机电开关机制一致。所有三种双稳态[2]轮烷的基态平衡性质在所有环境中都反映了分子结构。这些结果为通过分子结构控制MSTJ表现出的电子性质提供了直接证据。
