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.