**Abstract**

Ferrocene is a good electron donor, and as such has been used to test asymmetric conduction (rectification) in molecules that contain ferrocene. Of the five ferrocene-containing molecules that rectify (structures 11, 15, 19, 20, and 22), the last (22) exhibits a record rectification ratio, which should be a dramatic incentive for searching for more high-efficiency rectifiers.

**Keywords:** ferrocene, unimolecular electronics, rectification ratio, highest occupied molecular orbital, Aviram-Ratner proposal of 1974
