Synthesis of the stable ordered conjugated polymer poly(dibromodiacetylene) from an explosive monomer

Dibromobutadiyne is an extremely unstable compound that explodes at room temperature, even under inert atmosphere. This instability has limited the studies of dibromobutadiyne almost entirely to spectroscopic characterization. Here we report an approach to control the reactivity of dibromobutadiyne, via topochemical reaction in cocrystals, leading to the ordered polymer poly(dibromodiacetylene), PBDA. At low temperatures (-15 to -18 °C), dibromobutadiyne can form cocrystals with oxalamide host molecules containing either pyridyl or nitrile side groups, in which halogen bonds align the dibromobutadiyne monomers for topochemical polymerization. The cocrystals with the bis(nitrile) oxalamide host undergo complete ordered polymerization to PBDA, demonstrated by solid-state MAS-NMR, Raman, and optical absorption spectroscopy. Once formed, the polymer can be separated from the host; unlike the monomer, PBDA is stable at room temperature. Defusing: The reactivity of highly unstable dibromobutadiyne can be controlled by forming cocrystals with oxalamides at low temperature. Topochemical polymerization of dibromobutadiyne monomers leads to the first conjugated polymer containing bromine substituents on the backbone.