Towards efficient molecular wires and switches: the Brooker ions

In search of materials which may function as molecular wires or switches, analytical models have suggested that the Brooker ions should be particularly interesting. We study them in detail using ab initio, semi-empirical and specially-designed empirical techniques, predicting molecular geometries, charge distributions, and conductivities. Provided molecular symmetry is maintained, odd polyenes and Brooker ions NH2-(CH)+ 2n - 1 - NH2 are shown to conduct significantly better than even polyenes, but the advantage becomes a simple multiplicative factor once solitons form (chains of length ca 20 A). Symmetry lowering is predicted to dramatically decrease the conductivity but introduces the possibility that the Brooker ions may function as molecular switches, having greatly enhanced, switchable, non-linear optical properties.