Ethynylated Acene Synthesis and Photophysics for an Organic Chemistry Laboratory Course

An operationally simple, reliable synthesis of ethynylated acenes suitable for an upper-division undergraduate organic chemistry laboratory course has been developed. This experiment requires students to synthesize two acene derivatives and can be completed in 6-8 laboratory sessions (3 h each); a shorter experiment could be realized in the synthesis of only one product. Synthesis is carried out by first treating a terminal alkyne with n-butyllithium in an oven-dried flask under nitrogen at 0 °C. An acene quinone is added, which produces a doubly ethynylated diol. Dehydration with SnCl2/HCl yields a bis(ethynylated) acene, which is purified via a short pad or column of silica gel. The intense colors of the products allow for great ease in determining reaction completion and following the products in chromatography. UV-vis and fluorescence spectroscopy may be used to better understand the effect of molecular structure on electronic properties.