Synthesis and grafting properties of functionalized oligo(para-phenylene)s

For the purpose of grafting conjugated molecules on metal or oxide electrodes (which is an essential step towards a new generation of reliable organic light emitting diodes), we have synthesized soluble oligocyclohexadienes (12 cyclic units) by anionic polymerization and functionalized them by carboxylic acids, thiol and siloxane. Aromatization of the oligomer to oligo(para-phenylene) (OPP) is carried out by dehydrogenation with chloranil. The adsorption of the carboxylic oligo(para-phenylene) derivatives on indium tin oxide powder is investigated by solution equilibration. In tetrahydrofuran (THF) an equilibrium constant of K = 21 500 1 · mol−1 and a maximum surface coverage (Nmax) of 4 μmol/m2 are obtained by using the Langmuir equation. A characteristic area of 40 Å2 per molecule is inferred from the surface density of absorbed oligo(para-phenylene), which indicates that a densely packed monolayer of vertically adsorbed molecules is formed.