We prepared a molecular photodiode system in which the photocurrent direction can be switched by choosing the wavelength of an irradiating light. The molecular system is composed of two types of helical peptides that carry different chromophores and have different directions of dipole moments when they are immobilized on gold. The mixed, self-assembled monolayer generated an anodic photocurrent when one of the two chromophores was photoexcited, whereas the photocurrent switched to being cathodic when the other chromophore was photoexcited. The opposite current response arises from the dipole moment of each helical peptide, which accelerates electron transfer in the same direction.

Helical peptides of 8mer, 16mer, and 24mer carrying a disulfide group at the N‐terminal and a ferrocene moiety at the C‐terminal were synthesized, and they were self‐assembled on gold by a sulfur–gold linkage. Infrared reflection–absorption spectroscopy and ellipsometry confirmed that they formed a monolayer with upright orientation. Cyclic voltammetry showed that the electron transfer from the ferrocene moiety to gold occurred even with the longest 24mer peptide. Chronoamperometry and electrochemical impedance spectroscopy were carried out to determine the standard electron transfer rate constants. It was found that the dependence of the electron‐transfer rates on the distance was significantly weak with the extension of the chain from 16mer to 24mer (decay constant β = 0.02–0.04). This dependence on distance cannot be explained by an electron tunneling mechanism even if increased hydrogen‐bonding cooperativity or molecular dynamics is considered. It is thus concluded that this long‐range electron transfer is operated by an electron hopping mechanism. Copyright © 2007 European Peptide Society and John Wiley & Sons, Ltd.

Two types of peptide nanotubes, one is prepared from an amphiphilic peptide having a right-handed helix segment and the other from that having a left-handed helix segment, are shown to transform the morphology into a vesicle by membrane fusion due to stereo-complex formation between these helical segments.

The assembly of molecular architectures on the basis of molecular dipoles is proposed here to be a promising tool for construction of nanomaterials and nanodevices. Three kinds of building blocks having dipoles are discussed; helical peptides, cyclic β-peptides, and oligo(phenylene ethynylene)s having donor and acceptor substituents. Secondary interactions involving molecular dipoles are shown to be effective to control precise molecular shapes and to assemble the building blocks in a regular manner. Furthermore, molecular dipoles can generate a strong electric field at the nanoscale, which is useful for the promotion or suppression of electron transfer processes. Organic molecules with strong dipoles will therefore be applicable to various fields, such as molecular electronics and medical chemistry, as functional nanomaterials. It is expected that the chemistry of dipolar molecules will lay a firm foundation for a new interdisciplinary field, that of “molecular dipole engineering”.