Electrical rectification in betaine derivatives

We theoretically investigate the electric rectification in an organic two terminal push-pull molecular device using a combination of ab initio techniques. Our main finding is that the electric rectification is extremely sensitive to the length of the chain, undergoing a complete switching after a specific chain length. This unique process occurs for betaine-like donor-π bridge-acceptor systems and is directly associated with a conjugated bridge in the presence of an external electric field. The conjugated bridge between the donor and acceptor groups is composed of oligoethylene with sizes ranging from 0 to 10 C=C units. The appearance of electric rectification occurs when the bridge size is equal to 5 units and is complete for those larger than 6 units (i.e., full inversion). This new electronic effect is advantageous for the design of large hybrid organic/inorganic circuits with an increased majority carrier flow that is necessary for the emerging needs of nanotechnology.