Configuration- and Conformation-Dependent Electronic Structure Variations in 1,4-Disubstituted Cyclohexanes Enabled by a Carbon-to-Silicon Exchange

Cyclohexane, with its well-defined conformers, could be an ideal force-controlled molecular switch if it were to display substantial differences in electronic and optical properties between its conformers. We utilize σ conjugation in heavier analogues of cyclohexanes (i.e. cyclohexasilanes) and show that 1,4-disubstituted cyclohexasilanes display configuration- and conformation-dependent variations in these properties. Cis- and trans-1,4-bis(trimethylsilylethynyl)cyclohexasilanes display a 0.11 V difference in their oxidation potentials (computed 0.11 V) and a 0.34 eV difference in their lowest UV absorption (computed difference between first excitations 0.07 eV). This is in stark contrast to differences in the corresponding properties of analogous all-carbon cyclohexanes (computed 0.02 V and 0.03 eV, respectively). Moreover, the two chair conformers of the cyclohexasilane trans isomer display large differences in electronic-structure-related properties. This enables computational design of a mechanically force-controlled conductance switch with a calculated single-molecule ON/OFF ratio of 213 at zero-bias voltage