Theoretical study of building blocks for molecular switches based on electrically induced conformational changes

We present an investigation of building blocks for molecular torsional switches made up of two distinct aromatic moieties, possibly bonded through one or more acetynil groups. The mechanism of operation is based on the action of a static electric field perpendicular to the ring-ring bond, which can modulate the torsional angle and, as a consequence, the inter-ring conjugation. The action of the perpendicular electric field on the dihedral angle is shown to increase, as a result of the inclusion of suitable substituents on the aromatic rings. By computing the response of the electron density of a molecule, with an excess electron, to a longitudinal electric field, we show that the intramolecular electron transfer is sensitive to the torsional angle. This feature can be conveniently rationalized in terms of a potential barrier which is created along the molecule as the dihedral angle varies from the co-planar to the perpendicular position. (c) 2005 Elsevier B.V. All rights reserved.