Electric Field Effect of Helical Peptide Dipole on Oligo(phenyleneethynylene) in the Conjugate with Respect to Its Electronic Structure, Molecular Orientation, and Assembly Formation

摘要

Construction of nanometer-scaled well-defined structures has been of great interest for developing functional materials and devices in various fields from electronics to medical applications. Applying organic molecules to this challenge is expected to have several advantages over conventional top-down strategy, because organic molecules can be freely designed to modify the size and properties, and they can be built into a regular structure by self-assembling processes. As shown in sophisticated molecular-based structures in nature, control of non-covalent interactions is a key to construction of well-defined structures. Hydrogen-bonds, electrostatic interactions, and CH-π interactions have been used to form regular molecular structures. Recently, another interaction mode, dipole-dipole, has been successfully utilized to realize a planer triangle geometry of a helical peptide array. In this study, a novel conjugate of a helical peptide and oligo(phenyleneethynylene) (OPE) is proposed (OPEn9, Figure 1). OPE has demonstrated many attractive functions such as molecular electric wire, switch, and efficient fluorescence emitter. In our conjugate, not only the helical peptide unit but also the OPE unit have a dipole with the nitro attachment on it. A control compound without a peptide was also prepared (OPEnAc, Figure 1). In the present work, we have studied the effects of the helical peptide dipole on the electronic structure of the OPE unit and on the molecular orientation of the OPE unit in the conjugate, and further clarified the dipole-dipole interaction in the molecular assembling processes such as monolayer formation on a metal surface and an air/water interface.