Preparation of Ordered Polyacetylene by Solid-State Polymerization in Nanoscale Confinement

We report a novel, highly effective strategy for controlling the synthesis of polyacetylene as a guest in an organic host crystal by monitoring in situ an elimination–condensation polymerization reaction. Specifically, in this process, the polymer material is forced to have its chains extended and aligned such that translational periodicity applies, producing a bond alternation potential that has a symmetric double minimum. The synthetic approach used is photochemical elimination of iodine from a conjugated diene, (E,E)-1,4-diiodo-1,3-butadiene, which forms a commensurate and fully ordered urea inclusion compound. Photochemical cleavage of the terminal C–I bonds results in elimination of iodine from the single crystal and formation of C–C bonds between adjacent radicals to produce the conjugated 1,8-diiodo-1,3,5,7-octatetraene and subsequent longer polyene species. The combination of in situ crystal mass-loss measurements and vibrational Raman spectroscopy demonstrates clearly the presence of new polyene ...