Crystal-to-Crystal Transformation and Site Selectivity upon Bromination of a Polydiacetylene

AbstractBromine interacts with single crystals of poly-l,6-di-N- carbazolyl-2,4-hexadiyne to give homogeneous materials which have gained 3–8 Br atoms covalently bonded to carbon per polymer repeat unit. 13C CP-MAS NMR spectra show that the initial stage of the reaction is bromination of the carbazole moieties at the 3,6 positions. This initial stage is an anisotropic reaction resulting in a crystal-crystal transformation. In products containing 6 Br atoms per repeat, the results are consistent with addition of bromine to the triple bond and the conversion of the polydiacetylene structure to a mixed polyacetylene structure. Higher bromination levels (up to 8 Br per repeat) result in further addition to the multiple bonds of the backbone, disrupting conjugation.