RAPID SOLUTION AND SOLID-PHASE SYNTHESES OF OLIGO(1,4-PHENYLENE ETHYNYLENE)S WITH THIOESTER TERMINI - MOLECULAR SCALE WIRES WITH ALLIGATOR CLIPS - DERIVATION OF ITERATIVE REACTION EFFICIENCIES ON A POLYMER SUPPORT

The syntheses of soluble oligo(2-alkyl-1,4-phenylene ethynylene)s via an iterative divergent/ convergent approach starting from 1-(diethyltr iazyl)-3-alkyl-4-[(trimethyl are described. When the solublizing alkyl group is an ethyl substituent, the monomer, dimer, tetramer, and octa mer can be synthesized. The octamer, however, is only minimally solubl e. When the alkyl substituent is 3-ethylheptyl or dodecyl, the compoun ds are easily dissolved even at the 16-mer stage. The 16-mer is 128 An gstrom long in its near-linear extended conformation. At each stage in the iteration, the length of the framework doubles. Only three sets o f reaction conditions are needed for the entire iterative synthetic se quence: an iodination, a protodesilylation, and a Pd/Cu-catalyzed cros s coupling. Synthesis of the dodecyl-containing 16-mer was also achiev ed on Merrifield's resin using the iterative divergent/convergent appr oach. The oligomers were characterized spectroscopically and by mass s pectrometry. The optical properties are presented which show that at t he octamer stage, the optical absorbance maximum is nearly saturated. The size exclusion chromatography values for the number average weight s, relative to polystyrene, illustrate the tremendous differences in t he hydrodynamic volume of these rigid rod oligomers verses the random coils of polystyrene. These differences become quite apparent at the o ctamer stage. Equations were derived for assessing the efficiency of t he polymer-supported reactions based on resin weight; differences, mol ar concentration differences, and elemental analysis data. Each of the se methods' limitations are discussed. Attachment of thiol end groups, protected as thioacetyl moieties, was achieved. These serve as bindin g sites for adhesion to gold surfaces. In some cases, one end of the o ligomeric chains is capped with a thiol group so that the surface atta chments to gold could be studied. In other cases, thiol groups are aff ixed to both ends of the molecular chains so that future conduction st udies could be done between proximal metallic probes. The rigid rod co njugated oligomers may act as molecular wires in molecular scale elect ronic devices, and they also serve as useful models for understanding analogous bulk polymers.