Cross‐conjugation

Cross‐conjugation, even though very common in chemistry, has only sparsely been visited by experiment or by theory. Until very recently, this form of conjugation, in which two separate conjugated branches are linked to the same carbon atom which is part of a (shared) double bond, was considered to be much less able to promote electron delocalization than through‐conjugation. Therefore, exploiting cross‐conjugation to design new materials was considered difficult and not very promising. In this article, we show that this view, at least for neutral molecules in their electronic ground state, is essentially correct. For cross‐conjugated radical ions, the situation is different: There is appreciable charge delocalization across the bifurcation point, i.e., the point where the two conjugated branches meet. Simple Hückel molecular orbital considerations show that the connectivity pattern encountered in cross‐conjugation will lead to enhanced electron delocalization effects. This observation, confirmed by density functional calculations, also applies for electronically excited species. Therefore, cross‐conjugation may be exploited to build molecular switches or may be used to design devices such as molecular transistors. © 2011 John Wiley & Sons, Ltd. WIREs Comput Mol Sci 2011 1 477‐486 DOI: 10.1002/wcms.16 This article is categorized under: Structure and Mechanism > Molecular Structures Structure and Mechanism > Computational Materials Science