Extended 2,2'-Bipyrroles: New Monomers for Conjugated Polymers with Tailored Processability

Abstract

The synthesis of 2,2'-bipyrroles substituted at positions 5,5' with pyrrolyl, N-methyl-pyrrolyl and thienyl groups and their application in the preparation of conducting polymers is reported herein. The preparation of these monomers consisted of two synthetic steps from a functionalized 2,2'-bipyrrole: Bromination of the corresponding 2,2'-bipyrrole followed by Suzuki or Stille couplings. These monomers display low oxidation potential compared to pyrrole because of the extended length of their conjugation pathway. The resulting monomers can be polymerized through oxidative/electropolymerization. Electrical conductivity and electrochromic properties of the electrodeposited polymeric films were evaluated using 4-point probe measurements and cyclic voltammetry to evaluate their applicability in electronics.

Keywords: 2,2′-bipyrrole; conjugated polymer; electropolymerization; polypyrrole; pyrrole.

Figure 1

Structures of 2,2′-bipyrroles 1a–c.

Figure 2

Synthesis of 2,2′-bipyrroles 1a–c (G = 2-pyrrolyl, 2-(N-methylpyrrolyl) and 2-thienyl, R = Et).

Figure 3

Cyclic voltammograms of 2,2′–bipyrrole monomers in THF (10 mM) + 0.1 M TBAP. The voltammograms correspond to 1b (a), 1c (b), and 1a (c). Working electrode during quaterpyrrole electropolymerization (d) (R = Et).

Figure 4

2,2′-Bipyrrole oligomers in the cyclic voltammetry media after 100 cycles shown by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) spectrometry: 1c (a) and quaterpyrroles 1a and 1b (b,c) (R = Et).

Figure 5

FE-SEM images of 1c (a,c) and 1b (b,d).

Figure 6

Monomer free voltammograms of 1b (a) and 1c (b). Electrochromic behavior of the films observed during the cyclic voltammetry of 1b (c) and 1c (d) (R = Et).