In press, in Chemistry of Materials (doi.org/10.1021/acs.chemmater.9b03644).
The theory that underlies the reason for this article is addressed in "Bond Alternation In Infinite Periodic Polyacetylene: Dynamical Treatment Of The Anharmonic Potential," then the history of the material is exhaustively reviewed in "Polyacetylene: Myth and Reality" (open access, so you've no excuse to not read it). The preparation of the starting material, di-iodo-butadiene, C4H4I2, in urea, is published in "Commensurate Urea Inclusion Crystals With The Guest (E,E)-1,4-Diiodo-1,3-Butadiene."
I'm also very happy to be able to officially acknowledge my use of the Syracuse University Academic Virtual Hosting Environment (AVHE) as part of this work, which was involved in everything from periodic DFT calculations and the anharmonic treatment of polyacetylene on the electronic structure side, to cleaning up crystal cells of the polyacetylene-urea complexes for the generation of images in VMD and UberPOV – why just make a picture when you can, at least, make a method-consistent one?
As an aside, this is also my first experience using GIMP for a production-quality graphic – in this case, in the form of a proposed journal cover image (below. We'll see if it gets accepted in the coming month or so).
This GIMP use was instigated by originally formatting my MPB post-repair to Case-sensitive APFS three years ago, for which Photoshop refused to install with a widely-posted but little-addressed "Case-sensitive drives not supported" error (for which the Adobe solution remains "don't do that"). After a small learning curve, I'm pleased to say that GIMP is a hell of a program, well worth the price, and is just as pleasant an experience in Ubuntu 18.04 as it is in OS X 10.15 – a tidy sum saved each year for the 0.2% of features actually needed in either program to do the above.
Steluta A. Dinca, Damian G. Allis, Michael D. Moskowitz, Michael B. Sponsler, Bruce S. Hudson
Abstract: 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 chains and loss of iodine from the urea substructure. The first few product oligopolyenes exhibit very strong Raman scattering with the most intense vibrational features decreasing in frequency for longer chains approaching an asymptotic limiting frequency that mimics the behavior of conjugated polyenes of known lengths from previous vibrational Raman studies. With extensive irradiation, the mass loss approaches that anticipated from the crystal stoichiometry and, at the same time of irradiation, the Raman intensity largely disappears. These results demonstrate that the reaction reported here proceeds to completion, leading to a quasi-one-dimensional array of isolated polyacetylene chains that are constrained to be in a continuous extended, all-trans conformation within the tunnels formed by the urea crystal lattice.
And Happy Leap Day (a first after nearly 20 years of this domain existing).