New molecules of the type D-have been shown to form Pockels-Langmuir monolayers at the air-water interface and Langmuir-Blodgett films over glass or A1 substrates (D, one-electron donor; , covalent bridge (urethane); A, strong one-electron acceptor BHTCNQ or weak two-electron acceptor HMTCAQ). Assemblies 1| --| 2 (Mb M2, conventional metallic thin films; D, strong one-electron donor; A, strong one-electron acceptor) had been predicted in 1973 to be one-molecule-thick rectifiers of electrical current. When A is BHTCNQ, monolayers are formed if D is either pyrene (strong donor) (area per molecule at film collapse, Ac = 53 Á2/molecule; differential surface tension at collapse, IIC = 28.2 mN/m), (dodecyloxy)phenyl (weak donor) (Ac = 50 Á2, Ilc = 20.2 mN/m), or (bis(dodecyl)amino)phenyl (medium donor) (Ac = 54 A2, IIC = 45.9 mN/m). When A is HMTCAQ, monolayers are formed if D is (bis(dodecyl)amino)phenyl (Ac = 58 Á2, IIC = 22.3 mN/m). Thus, greasy tails are found to be generally helpful in orienting D-molecules in monolayers (even though they may slow down electron conduction through the molecules).

Molecular materials of the form electron donor-sigma-bridge-electron acceptor (D-s-A) have been synthesized and incorporated into non-centrosymmetric Langmuir-Blodgett (LB) multilayer structures. Electrical characterization has been performed using a metal|(Z-type LB film)|metal (M|LB|M ) junction construction. Current density-voltage data demonstrate striking rectification behaviour. Computational modelling of the electronic structure of the material has been carried out using a first principles, density functional approach. Possible conduction mechanisms are discussed with reference to the results of this modelling.

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