Fast switching from isotropic liquids to nematic liquid crystals: rotaxanes as smart fluids

Triangular cyclic rotaxanes: Size, fluctuations, and switching properties

We examine one of the simplest cyclic rotaxanes-a molecule made from three rods with variable length between 0 and L. This [3]rotaxane, unlike a traditional molecule, shows significant size and shape fluctuations. We quantify these using a number of different measures. In particular, we show that the average angles are [Formula: see text], and [Formula: see text] and the most populated lengths lie at [Formula: see text], and [Formula: see text] The triangles are usually obtuse. We discuss the area allowed within the triangle for inclusion compounds. Inspired by the linear rotaxane switches, we also consider the statistical mechanics of switching when stations with attractive interactions promote small-cycle areas.

Acid-Base Switchable [2]- and [3]Rotaxane Molecular Shuttles with Benzimidazolium and Bis(pyridinium) Recognition Sites

For the purpose of developing higher level mechanically interlocked molecules (MIMs), such as molecular switches and machines, a new rotaxane system was designed in which both the 1,2-bis(pyridinium)ethane and benzimidazolium recognition templating motifs were combined. These two very different recognition sites were successfully incorporated into [2]rotaxane and [3]rotaxane molecular shuttles which were fully characterized by ¹ H NMR, 2D EXSY, single-crystal X-ray diffraction and VT NMR analysis. By utilizing benzimidazolium as both a recognition site and stoppering group it was possible to create not only an acid/base switchable [2]rotaxane molecular shuttle (energy barrier 20.9 kcal⋅mol^-1 ) but also a [3]rotaxane molecular shuttle that displays unique dynamic behavior involving the simultaneous motion of two macrocyclic wheels on a single dumbbell. This study provides new insights into the design of switchable molecular shuttles. Due to the unique properties of benzimidazoles, such as fluorescence and metal coordination, this new type of molecular shuttle may find further applications in developing functional molecular machines and materials.

A Two-Stroke, Two-Cylinder Piston Rotaxane Motor

We introduce a model for a rotaxane motor. This uses two major themes of rotaxane physics, that is, the ability to change the potential of different regions of the axle (switching) and the entropy associated with free rings. The motor is based on free rings being trapped and released by potential stripes or stations. We calculate the power produced by such a motor, which is in the femtoWatt range. The power is proportional to the square of the number of rings.

Isotropic and nematic liquid crystalline phases of adaptive rotaxanes

We describe the thermodynamics of a solution of rotaxanes which can change their length from a short state of length L to a long state of length qL in response to their surrounding environment. We call these rotaxanes "adaptive." We show that such a system can exhibit both isotropic and nematic liquid crystalline phases. The system shows several interesting kinds of behaviour. First we predict that the fraction of short-length rotaxanes increases linearly with concentration and is a maximum at the critical concentration that marks the isotropic to nematic transition. Second, the critical concentration shows a minimum at a certain value of q. Our model suggests that the effect of adaptive length changes is most dramatic at small q and where the long state is slightly favoured.