Exploring Antiaromaticity in Single Molecule Devices

Funding :

Comunidad de Madrid

2019-T1/IND-16384

Duration:

The concept of aromaticity has captivated chemists for many years. It is characterised by the additional stability and lower reactivity of planar, cyclic hydrocarbons possessing 4n + 2 delocalised π-electrons (where n is any integer (except zero) over olefinic analogues, as codified by Hückel. Aromatic compounds display large anisotropic diamagnetic susceptibilities due to their ability to sustain ring currents under applied magnetic fields. Benzene is the archetypal aromatic molecule with six π electrons. Breslow extended the concept by describing cyclic, planar compounds with 4n π electrons as antiaromatic, which are chemically less stable than their olefinic counterparts and which sustain paratropic ring currents. Antiaromatic compounds are predicted to give higher conductance in molecular junctions compared to corresponding aromatic or non-aromatic conjugated compounds. It has been suggested that the relative conductance can be predicted based on the ease to which the π-system is perturbed due to a shift of electron density between anchor groups. Aromatic molecules are predicted to be less conductive as they will resist this charge redistribution (which disrupts aromatic bonding). Conversely, antiaromatic compounds favour a redistribution which disrupts cyclic conjugation, leading to higher conductance. Furthermore, antiaromatic molecules tend to have smaller HOMO-LUMO gaps compared to aromatic and non-aromatic molecules. When connected to electrodes, the frontier molecular orbitals of antiaromatic molecules might be expected to lie closer to the Fermi level, also contributing to higher conductance. This project aims to investigate these claims and to develop a deeper understanding of the role of this fundamental concept in single molecule junctions.

This project was funded under the Atracción de Talento de la comunidad de Madrid (Modalidad 1).