What Can Be Learned From The Polymerization Of A Pyridine-Based Two-Component System

Stable poly (4-vinyl pyridine)/pyridine gels prepared by dissolving solid polymer in pyridine (the equimolar ratio of the pyridine moieties to the pyridine solvent molecules) exhibit sensor properties rapidly and reversibly increasing their conductivity upon irradiation by light in the UV-Vis and NIR ranges. Both ionic and electronic mechanisms of conductivity were detected. The gels behave as polyelectrolytes involving the positively charged pyridine moieties and negatively charged saturated chains held together by a network of hydrogen bonds between the charged and neutral species. This interpretation is corroborated by the cryo-TEM images of the gel samples resembling chains of beads and the analysis of FT-IR and H-1-NMR spectra. Photoinduced proton transfer can thus be responsible for the observed ionic conductivity of the gels. Exposing gels to the ambient light can bring about ring opening of the pyridine moieties and of the free pyridine molecules with subsequent polycondensation of the initially formed 5-amino-2,4-pentadienal. The oligomers of the latter, aza-analogs of polyacetylene, can serve as molecular wires providing the electronic component of electrical conductivity. These oligomers can also contribute to the ionic conductivity and further stabilize the gels by cross-linking of the separate polymer chains.