Synthesis and properties of low-bandgap zwitterionic and planar conjugated pyrrole-derived polymeric sensors. Reversible optical absorption maxima from the UV on the near-IR

Article abstract of DOI:10.1021/ja00121a001

Described are the polymerizations of three new dibrominated carbonyl-stabilized ylide monomers using copper-bronze in DME to afford polymers that are soluble in common solvents and have unique optical and electronic properties. The first monomer is a zwitterionic N-butylpyrrolinium oxide derivative which, upon polymerization, gives a polymer that has a strong optical absorbance at 520 nm in CCl₄. An interunit ionic interaction is proposed to explain this large red-shifted band. Bronsted bases and Lewis bases induce a reversible structural change in the polymer to give bathochromic shifts from the visible to the near-IR spectral region. Upon mild reduction of the zwitterionic polymer with Pd/C and H₂ (1 atm), some of the extended conjugation is lost, but a polymer forms that has an enormous optical absorption maximum range from the near-LV (290 nm) to the near-IR (886 nm) depending on the solvent or hydroxide concentration. A sample of the reduced polymer can be dispersed in platicized poly(vinyl chloride). The flexible polymer composite reversibly changes from dark blue-brown in aqueous sodium hydroxide to bright yellow-orange in aqueous HCl. The second monomer, a zwitterionic N-dodecylpyrrolinium oxide derivative, was also synthesized in three steps from pyrrole and, upon polymerization, gives rise to a polymer which also responds reversibly toward Bronsted and Lewis bases. This polymer can be solution cast into flexible free-standing films. The third monomer is a zwitterionic N-[oligo(ethylene glycol) monomethyl ether]pyrrolinium oxide derivative which, upon polymerization, affords a polymer that not only responds reversibly toward Bronsted and Lewis bases but also is water soluble and optically sensitive toward the addition of specific salts. The presence of the oligoethylene substituents is critical for the dramatic ionochromic response. Additionally, Pd-catalyzed cross-coupling methodology can be used for the incorporation of the N-butylpyrrolinium oxide monomer unit into an AB-type oligomeric system where the B component is a 1,4-phenylene moiety.