Macrocycles as Hosts: A Strategy to Isolate and Deiodinate Poly(diiododiacetylene) to Form Carbyn

Carbyne is a theoretical but heretofore unrealized sp-hybridized allotrope of carbon which is predicted to have high tensile strength, strong conductance, UV/vis absorption, and a small bandgap. One possible precursor to carbyne is poly(diiododiacetylene), or PIDA, which is a carbon-rich polymer with iodine side groups that, if dehalogenated, could yield carbyne. Past methods for the elimination of iodine from PIDA have been unsuccessful due to cross-linking and chain aggregation, issues that this project seeks to resolve. This work focuses on the synthesis of two target macrocycles that will act as hosts to arrange diiodobutadiyne guest molecules into the proper spacing in a cocrystal to allow for topochemical polymerization. The macrocycles contain pyridyl functionalities that can form halogen bonds with the iodoalkyne groups of the guests, along with oxalamide moieties that control the solid-state geometry by self-assembly into a one-dimensional hydrogen-bonding network. In this way, the macrocycles form a columnar structure that will encapsulate the resulting polymer, forming a polyrotaxane. The first target features flexible alkyl chains that link the oxalamides and pyridines; its synthesis has been complicated by the need to make a small molecule amine that is volatile at room temperature and challenging to isolate. The second macrocycle has benzyl linkers which introduce more rigidity and allow for each macrocycle to accommodate the monomer fully. This target required the robust synthesis of an asymmetric bis-alkynyl benzene, which was coupled to a dibromopyridine to form the "half ring." The half ring has successfully been homocoupled to form the macrocycle. Future work will be geared towards synthesizing more material, which will be used in cocrystal experiments with diiodobutadiyne to form PIDA in pursuit of the carbon allotrope carbyne.