Mesomolecular Anilines*: New Horizons in Electrically Conducting Organic Materials

MacDiarmid, University of Pennsylvania

 Technology Issues: (i) New Grant: Polyaniline has a conductivity ~104 smaller than its projected intrinsic value which approaches
that of copper. How can its conductivity be increased?
(ii) Old Grant: Evaluate polypyrrole films as electrodes.

Objectives: (i) New Grant: Study mesomolecular anilines with particular emphasis on their isomeric forms--forms which are predicted to control the conductivity of polyaniline. Evaluate new, unexpected properties of oligomers. (ii) Old Grant: Determine properties of polypyrrole films as a function of thickness and application as electrodes.

Approach:

  • Synthesize and completely characterize mesomolecular anilines.
  • Search for evidence of isomeric forms in the above compounds.
  • Deposit films of polypyrrole by our in-situ method and evaluate:
    a) as a function of thickness.
    b) as electrodes on poly(VDF-TrFE).

Accomplishments:

  • Synthesis and characterization of (aniline)n (n=4,8,16) accomplished.
  • Proved that the tetramer (n=4) exists in two different isomeric forms. [Fig.]
  • Films of polypyrrole show a "memory effect" dependant on the original substrate surface; they serve as excellent electrodes as a substitute for Au on a piezoelectric polymer.
  • Octaaniline (n=8) serves as an excellent sensor for VOCs.

Impact & Transition:

  • Each positional isomer can, in principal, also exist in both cis and trans forms. [Fig.] The total number of possible isomeric forms increases enormously as n increases.
  • Synthesis of polyaniline in a given isomeric form will greatly increase its conductivity.

In-situ deposited polypyrrole electrodes show very considerable promise in electro-acoustic applications.

 *A mesomolecular aniline is an oligomer of aniline (short chain aniline) in which the band structure of polyaniline is approaching complete development