Contributed
Photoinduced proton and electron transfer within poly(4-vinylpyridine)/pyridine gel

Gels based on poly(4-vinylpyridine)/pyridine compositions possess an unusual variety of light and heat induced phenomena that are rationalized by delocalization and localization of the charge carriers within the semi-solid structures involving multiple intra- and intermolecular interactions. The past twenty years of investigations of the pyridine-based polymer gels demonstrated the presence of two types of electrical conductivity: ionic and electronic.^1,2 The sensitivity of the gels electrical conductivity to irradiation in the UV-Vis-NIR ranges suggests a great diversity of their potential applications. At the same time, whereas the origin of the ionic conductivity is established, the origin and mechanisms of electrical conductivity remain obscure. The main past and present results on revealing the conductivity mechanisms within the pyridine-based compositions will be discussed.

The ionic conductivity stems from the photo-induced proton transfer from the -CH- groups of the aliphatic chains to the nitrogen atoms of the pyridine rings. This mechanism was confirmed by quantum mechanical calculations and experimentally by ¹⁵N solid state NMR in a gel samples enriched by ¹⁵N.

Whereas the ionic mobility was found to be within the same range as the proton mobility in ice (µ =1.8x10^-3), the electron mobility was significantly higher compared with the known semiconducting polymers (µ = 25 cm²V^-1s^-1). The relaxation times of the photo-response signal constant decay t₁ = 0.02 s in comparison with the temperature-induced relaxation constants decay t₁ = 0.148 s and t₂ = 17.11 s were measured.

The role of the reversible ring opening of the pyridine moieties upon irradiation and potential applications of poly(4-vinylpyridine)/pyridine compositions will also be discussed.

Reference: 1) Berestetsky, N. et al. J. Phys. Chem. B, 2008, 112, 3662; 2) Vaganova, E. et al. Pol. Network and Gels, Prague, 2018, Book of Abstract, 88.