Characterization and conductivity of Langmuir-Blodgett films prepared from an amine substituted oligo(phenylene ethynylene)

Villares, Ana and Lydon, Donocadh and Low, Paul and Robinson, Benjamin and Ashwell, Geoff and Royo, Felix and Pilar, Cea (2008) Characterization and conductivity of Langmuir-Blodgett films prepared from an amine substituted oligo(phenylene ethynylene). Chemistry of Materials, 20 (1). pp. 258-264. ISSN 0897-4756

Abstract

This paper reports the assembly of well-defined molecular films from 4-[4-(4-hexyloxyphenylethynyl)-phenylethynyl]-aniline (HBPEB amine), an oligomeric phenylene ethynylene (OPE) derivative, by means of the Langmuir–Blodgett technique. Initially, Langmuir films of HBPEB amine were prepared at the air–water interface and characterized with surface pressure vs area per molecule isotherms. Brewster Angle Microscopy was used to map the different phases of the monolayer at the air–water interface. UV–vis reflection spectroscopy showed a blue shift of 20 nm of the reflection spectrum of the Langmuir film with respect to the spectrum of a chloroform solution of HBPEB amine, which indicates that two-dimensional H-aggregates are formed at the air–water interface. The monolayers were transferred onto solid substrates with a Y-type deposition and a transfer ratio of 1. The excellent transfer characteristics permitted the construction of films comprising up to 150 layers, with a uniform architecture. The LB films fabricated from HBPEB amine show a blue shift of ca. 30 nm with respect to the chloroform solution of HBPEB amine, likely arising from a change in the orientation of the molecular transition dipole with respect to the surface normal in the solid-supported films in comparison with the Langmuir films at the air–water interface. The current–voltage (I−V) characteristics of LB monolayers are unexpectedly symmetrical, the asymmetric contacts not being apparent from the observed I−V characteristics.