Vertical Step-Growth Polymerization Driven by Electrochemical Stimuli from an Electrode

Abstract

We present herein the vertical step-growth polymerization of a monomer A-B through individual A-A or B-B coupling driven by electrochemical switching of positive and negative bias on a self-assembled A or B electrode. The monomer Ru^II (bda)AB (bda=2,2'-bipyridine-6,6'-dicarboxylate), in which A and B are pyridine moieties with pendant carbazolyl and vinyl groups, could be dimerized at oxidative (ca. 1.0 V vs. Ag/Ag⁺ ) or reductive potential (ca. -1.8 V) to give a self-assembled Ru^II (bda)PA or Ru^II (bda)PB monolayer (P=pyridine with a pendant phosphonic acid) on ITO glass. This polymerization enabled the sequence- and topology-controlled synthesis of surface-confined molecular wires with single-molecule precision on an electrode. The electrocatalytic performance of the vertically orientated molecular wires for water oxidation increased with increasing molecular length and exceeded that of both the self-assembled monolayer and a randomly electropolymerized film, which have previously been studied as typical models.

Keywords: C−C coupling; electrochemistry; self-assembled monolayers; single-molecular assembly; step polymerization.