Synthesis of thiol-terminated conjugated oligomers for study of fast interfacial electron transfer

I have synthesized sets of thiol-terminated electroactive oligomers to study interfacial electron transfer. My collaborators and I have deposited self-assembled monolayers containing these oligomers to analyze how electrons tunnel through insulating molecular materials and to study whether electron tunneling can be harnessed for molecular devices. Specifically, I have explored further monolayers containing unconjugated ferrocene-terminated oligo(methylene) (OM) thiols (Chapter 1). I have synthesized ferrocene-terminated oligo(phenyleneethynylene) (OPE) (Chapter 2) thiols of lengths longer than previously reported. I have developed syntheses of ferrocene- and pyridine-terminated oligo(phenylenevinylene) (OPV) thiols (Chapters 3--4). I have explored preliminarily the synthesis of ferrocene-terminated oligo(phenyleneamide) (OPA) thiols (Chapter 5).;Thiol-terminated electroactive oligomers have been deposited with alkane thiol diluents as mixed self-assembled monolayers on gold. The resulting monolayers have been analyzed by ellipsometry and cyclic voltammetry. The rate of electron transfer between the electrode through the oligomer to the pendant electroactive center was measured either by chronoamperometry for slow rates or by the indirect laser induced temperature jump method for fast rates. We find the rate of electron transfer for most of the oligomers is slower through longer bridges than through shorter bridges.;For OM, we find a beta of 0.85 A-1 which agrees well with published values for sigma bond electron transfer. Electron transfer through pi-conjugated OPE is many orders of magnitude faster than through OM of the same length. However, facile rotation of adjacent phenylene groups around the intervening ethynylene bond in OPE may lower the pi-conjugation of this oligomer. Electron transfer through the more rigid, planar oligomer, OPV, is faster than through OPE especially at long bridge lengths. At distances shorter than 28 A, electron transfer through OPV is not limited by electronic tunneling through the bridge but may instead be limited by structural reorganization during the transfer process. To demonstrate the potential use of OPV as a molecular wire, I have synthesized a pyridine-terminated OPV thiol which can electronically connect coordinated metal centers like ruthenium to an electrode through an otherwise insulating monolayer. This thesis finishes with a discussion of oligomer synthetic methodology. I have attempted to synthesize OPA through an expedient convergent synthetic strategy.