Molecular Compasses and Gyroscopes with Polar Rotors: Synthesis and Characterization of Crystalline Forms

We report the highly convergent synthesis and solid-state characterization of six crystalline “molecular compasses” consisting of a central phenylene rotor with polar substituents, or compass needle, and two trityl groups axially connected by acetylene linkages to the 1,4-positions. Compounds with fluoro-, cyano-, nitro-, amino-, diamino-, and nitroamino substituents are expected to emulate the parent compound which was shown to form crystals where the central phenylene can rotate about its 1,4-axis with rate constants in the 103 −106 s-1 dynamic ranges near ambient temperature, depending on crystal morphology. With data from single-crystal X-ray diffraction analysis, solid-state CPMAS 13C NMR, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA), it is shown that a relatively small structural perturbation by a single polar group (F, CN, NO2, NH2) results in isomorphous structures with analogous properties. In analogy to the parent compound, crystals grown from benzene formed clat...