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/Et3N. 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/Et3N/MeCN. For the 2,6-dibromoarenes, the bis-arylvinylated derivative was the sole product in the presence of either Ph3P or (o-tol)(3)P, if provided with a small volume of Et3N/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 H-1 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.