engleski

Untangling the operation machanism of a light- driven phenylazoimidazolium out-of-equilibrium molecular machine

Rotaxanes are a class of mechanically interlocked molecules (MIMs) in which a macrocyclic ring encircles a molecular dumbbell-shaped axle. Its chemical properties are directed by supramolecular interactions between the chemical components of the rotaxane (the axle and the macrocycle) which are entangled in space.1 Rotaxanes often serve as a platform for design of molecular machines: systems that perform mechanical movements as a result of an appropriate external stimulus. Even more, since light can be used to trigger different reversible reactions, it is possible to use it as a fuel for molecular machines. In this work, imidazole, a heterocycle with a very versatile chemistry often used in supramolecular chemistry and MIMs, 2, 3 was introduced into the structure of the axle of the rotaxane as a part of the phenylazoimidazolium subunit, which is photoswitchable. This enabled the operation of the system using light. At the same time, because of its cationic properties it can serve as a station for a crown ether macrocycle. This dual role of imidazolium enables the control of the ring interaction with the photoactive unit. On the other hand, the axle also contains a secondary ammonium station for the macrocycle, which is the favored one when it is in its protonated form. Upon deprotonation of the ammonium, the ring shuttles towards the imidazolium, so also the pH control of the system is provided. The exposure of this interlocked architecture to two different external stimuli leads to formation of four species which differ amongst each other by thermodynamic, photophysical, and chemical properties. The unique properties of this system were studied through NMR spectroscopy and spectrophotometry. Beyond the interesting photophysical and photochemical aspects, this [2]rotaxane is attractive for the development of photoactive molecular machines and multi- responsive materials.

reaction network ; rotaxane ; crown ether ; mechanical bond ; E/Z isomer acidity ; supramolecular chemistry

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