Intramolecular torsion based molecular switch functionality enhanced in π-conjugated oligomolecules by a π-conjugated pendant group

Theoretical investigations of the variation of junction conductance with the intramolecular twist in π-conjugated oligomolecules induced by a pendant group and its effects on the enhancement in its molecular switch functionality are presented. The pendant group is found to introduce "through space" electronic coupling between the central phenyl group and its adjacent ethynylenes in the highest occupied molecular orbital, which opens an additional tunnel channel. Consequently, the π-conjugation in the backbone of the molecule is reinforced and the junction conductance along the molecular backbone gets elevated relative to the parent molecule. A 90° intramolecular twist angle of the molecule is regarded as the "OFF" state for its lowest conductance at this exactly perpendicular conformation, while the other twist angles including 0° are considered as "ON states" of the molecule. The pendant group raises the ratio of the junction conductance between the "ON" and "OFF" states by up to 2 orders of magnitude, thereby effectively enhancing its molecular switch functionality. © 2011 American Chemical Society.