Toward Isolated Molecular Wires:  A pH-Responsive Canopied Polypyrrole

Abstract

The design, synthesis, and electropolymerization of sterically hindered pyrrole derivatives are described. Endo and exo adducts of cyclopentadiene and N-phenylmaleimide were converted to give bicyclo[2.2.1]heptane-fused pyrrole monomers, in which a phenyl group is rigidly placed proximate the pyrrole fragment. Oxidative polymerization of these monomers affords highly conductive polypyrroles. The rigid molecular scafffold of the pyrrole monomers limits cross-communication between adjacent conducting strands and produces a defined narrow potential window of high conductivity dominated by intrachain polaronic charge carriers. The resultant loosely packed polymer chains allow for superior sensory properties. Notably, the electrical conductivity of oxidatively doped poly(7) could be reversibly modulated in aqueous electrolytes at pH 3−9.

Analysis of Conjugated Polymers Conductivity by in situ Electrochemical‐Conductance Method

“…[159] Conductivity of canopied-polypyrrole films also present a response to variations on the pH value ( Figure 14a). [160] An appreciable decrease in conductivity when the pH increases was observed. This is due to the loss of the polaronic state caused by the increase of the pH (Figure 14b).…”

“…The loss of conductivity is attributed to the deprotonation of the phenolic protons in the oxidized state, which it does not happen on acid conditions . Conductivity of canopied‐polypyrrole films also present a response to variations on the pH value (Figure a) . An appreciable decrease in conductivity when the pH increases was observed.…”

“…An appreciable decrease in conductivity when the pH increases was observed. This is due to the loss of the polaronic state caused by the increase of the pH (Figure b) . Polythiophene containing 2,4,6‐cycloheptatrien‐1‐one units also showed a decrease in conductivity when the pH increases .…”

“…This is due to the loss of the polaronic state caused by the increase of the pH (Figure 14b). [156,160] Polythiophene containing 2,4,6-cycloheptatrien-1-one units also showed a decrease in conductivity when the pH increases. [161] This is caused by aromaticity gained by the protonated polymer, which destabilizes the quinoid resonance.…”

Conducting-Polymer-Based Chemical Sensors: Transduction Mechanisms

“…16). 60,61 Due to the high porosity of poly-11 films imparted by this canopy, analytes can easily diffuse into the polymer film and therefore give real-time sensing responses in solid materials. The insulation of the pyrrole chains limits interchain charge hopping and hence, this system gives large responses when the conduction along a chain that is prevented by analyte reactions.…”