Electrical rectification by monolayers of three molecules

Rectification, i.e. asymmetrical electrical conduction by a Langmuir-Blodgett monolayer of dicyano{4-1-cyano-2-(1-hexadecylquinolin-1-ium-4-yl)vinyl]phenyl} methanide ( 1 ), occurs between both Al and Au electrodes: this rectification arises from the asymmetry of the molecule, and the interplay between the zwitterionic ground state D⁺-π-A⁻ and the less dissociated first electronic excited state D⁰-π-A⁰. Two more monolayer rectifiers have been found: 1-butyl-2,6-bis{2-4-(dibutylamino)phenyl] vinyl}pyridin-1-ium iodide ( 2 ) is an interionic rectifier with back charge transfer between the iodide ion and the pyridinium ring. 1a-4-(dimethylamino)phenyl]-1aH-1a-aza-1(2)a-homo(C₆₀-I_h)5,6]fullerene ( 3 ) is a moderate rectifier, with a rectification ratio of 2.