Improved Physical Properties and Rotational Dynamics in a Molecular Gyroscope with an Asymmetric Stator Structure

A molecular gyroscope consisting of a 1,4-diethynylphenylene rotator linked to trityl and triptycyl groups (3) showed significantly improved physical properties and faster rotational dynamics than analogous symmetric bis(trityl) (1) or bis(triptycyl) (2) structures. An activation energy of 7.9 kcal/mol for 3 was determined by 2H NMR. This is ca. 4−6 kcal/mol lower than that of compound 1. The different dynamics of the three compounds can be qualitatively understood in terms of their different packing coefficients.