Reversible Photoswitching of Rotaxane Character and Interplay of Thermodynamic Stability and Kinetic Lability in a Self-Assembling Ring-Axle Molecular System
Reversible Photoswitching of Rotaxane Character and Interplay of Thermodynamic Stability and Kinetic Lability in a Self-Assembling Ring-Axle Molecular System
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DOI：
10.1002/chem.201001409
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发表时间：
2010-01-01
影响因子：
4.3
通讯作者：
Credi, Alberto
中科院分区：
文献类型：
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作者：
Baroncini, Massimo;Silvi, Serena;Credi, Alberto
我们设计、合成和研究了一种可以在光照射下在热力学稳定的(拟紫杉烷)和动力学惰性的(轮紫杉烷)之间进行可逆相互转化的自组装体系。该体系由二苯并[24]冠-8环和由二苄基铵识别中心和两个偶氮苯端基组成的轴组成。轴上偶氮苯单元的异构体形式对各自的拟轮烷的稳定常数影响较小，但对穿线-脱线速率常数影响很大。事实上，在室温下，在乙腈中，环和车轴以EE异构体的形式在几秒钟内达到平衡，而ZZ轴的螺纹-脱环至少慢四个数量级。此外，我们还表明，通过去质子化二苄基铵识别中心实现的络合物稳定性的变化，影响了它的动力学行为。我们将这些实验的结果与通过使用竞争客体脱除(伪)轮烷时观察到的结果进行了比较，这种方法本身不会破坏环轴相互作用的稳定性。这项研究概述了可逆光化学控制螺纹和互锁化合物运动动力学的一般策略，并构成了构建能够像光化学驱动纳米机器一样行为的多组分结构的起点。
We have designed, synthesized, and investigated a self-assembling system that can be reversibly interconverted between thermodynamically stable (pseudorotaxane) and kinetically inert (rotaxane) forms by light irradiation. The system is composed of a dibenzo[24]crown-8 ring and an axle comprised of a dibenzylammonium recognition site and two azobenzene end groups. The isomeric form of the azobenzene units of the axle has a little influence on the stability constants of the respective pseudorotaxanes but greatly affects the threading-dethreading rate constants. In fact, equilibration of the ring and the axle in its EE isomeric form occurs within seconds in acetonitrile at room temperature, whereas the ZZ axle threads-dethreads the ring at least four orders of magnitude slower. Moreover, we show that a change in the stability of the complex, achieved by deprotonating the dibenzylammonium recognition site on the axle, affects its kinetic behavior. We compare the results of these experiments with those observed upon dethreading the (pseudo)rotaxane by using a competitive guest for the ring, an approach which does not inherently destabilize the ring axle interaction. This study outlines a general strategy for the reversible photochemical control of motion kinetics in threaded and interlocked compounds and constitutes a starting point for the construction of multicomponent structures that can behave as photochemically driven nanomachines.