Highly Conjugated Molecules from Dibromonaphthyl Derivatives and 4-Vinylpyridine or 4-Acetoxystyrene by the Heck Reaction

Palladium-catalyzed coupling of 1,6- and 2,6-dibromonaphthyl derivatives with 4-vinylpyridine or 4-acetoxystyrene resulted in mono- and bis-arylvinylation depending on the choice of reaction conditions. For the 1,6-dibromoarenes, the mono-arylvinylated derivative at position-6 was the sole product in the presence of (o-tol)(3)P/Et(3)N. The bis-arylvinylated derivative was the major product, accompanied by a minor product, arylvinylated at position-6 and reduced at position-1, in the presence of (o-tol)(3)P/Et(3)N/MeCN. For the 2,6-dibromoarenes, the bis-arylvinylated derivative was the sole product in the presence of either Ph(3)P or (o-tol)(3)P, if provided with a small volume of Et(3)N/MeCN solvent, and the mono-arylvinylated derivative was the major product with larger solvent volume and higher haloarene ratio. Fluorescence intensities of 2,6-bis-arylvinylated products were 2 to 3 orders of magnitude higher than that of stilbene. Nematic phases, at relatively high temperatures, were observed for some of the rodlike molecules. Shown by (1)H NMR study, at the photostationary state of isomerization, smaller fractions of cis-form were obtained for molecules that exhibited larger fluorescence quantum yields. The results presented here are beneficial to the pursuit of nonlinear optical materials, fluorescent mesogens, photo- and electroactive materials.