Synthesis, characterization, and solid-state polymerization of cross-conjugated octatetraynes

Abstract

Two series of cross-conjugated 1,3,5,7-octatetraynes (1a–1l and 6a–6d) have been synthesized. UV–vis spectroscopic analysis shows that pendent groups connected to the cross-conjugated skeleton have little effect on the λmax energies, irrespective of whether the groups are electron withdrawing or donating. A number of the isolated products readily give crystals suitable for X-ray crystallography, and the solid-state structural properties of five derivatives (1k, 1l, 6a, 6c, and 6d) have been examined by X-ray crystallographic analysis. Parallel packing of the polyynes in the solid state indicates that four of the five samples are potentially suitable for topochemical polymerization, based on solid-state packing parameters θ, R, and d. Attempts to effect a solid-state reaction have been explored through UV–vis and γ-ray irradiation as well as thermal heating. The course of these reactions was monitored by differential scanning calorimetry (DSC) analysis, as well as UV–vis and solid-state 13C NMR spectroscopy (for 1d, 1j, 1k, and 6d), which offered evidence of polymer formation from these reactions. Structural determination of the product(s), however, remains elusive.