Theoretical Studies on Electronic Structures and NMR Spectra of Oligo(4-vinylpyridine)

Poly(4-vinylpyridine) was determined to possess conductivity in the experiment. In order to understand properties of the polymer, a series of 4-vinylpyridine oligomers were designed. The structures of these oligomers were optimized using density function theory (131717) at B3LYP/6-31G(d) level. The energy gaps and thermal stabilities of the oligomers were decreased when the chain lengths were increased. These properties were also decreased owing to the protonation of the pyridine ring. The holes were easily injected into the oligomers in the presence of hydrochloride. The electrons were conducted in the side chain composed of the pyridine rings rather than the main chain owing to the saturation of the main chain. The C-13 nuclear magnetic resonance (NMR) spectra and nucleus independent chemical shifts (NICS) of these compounds were calculated at B3LYP/6-31G(d) level. The chemical shifts of the carbon atoms connected with the nitrogen atoms in the protonated pyridines were moved upfield in comparison with those of the pyridines. The addition of hydrochloride on the pyridine ring in the oligomers led to the increase of the aromaticities, namely the aromaticities of the oligomers were obviously improved when the pyridine rings were protonated.