Solid-State Bromination of Poly(1,6-di-N-carbazolyl-2,4-hexadiyne): A 13C CP-MAS NMR Study

Article abstract of DOI:10.1021/ja00237a022

13C cross-polarization/magic-angle spinning (CP-MAS) NMR experiments at 50.36 MHz reveal that the solid-state reaction of the crystalline polymer poly(N-dicarbazolyl-2,4-hexadiyne) (poly-DCH) with liquid bromine results in the formation of covalent C-Br bonds in the polymer.The presence of bromine in these compounds results in loss of the signals arising from those carbon atoms directly bonded to or adjacent to bromine due broadening effects arising from dipolar coupling to the quadrupolar 79,81Br isotopes.Nevertheless, 13C CP-MAS NMR can identify carbon atoms more than two bonds removed from bromine and allows one to monitor semiquantitatively the course of the bromination.By comparison with model compounds it is shown that bromine effects selective electrophilic aromatic substitution at the 3,6 positions on the aromatic rings of the carbazole moiety, forming a polymer with four Br per repeat unit.At higher bromination levels addition to the multiple bonds in the backbone occurs.For the material of composition poly-DCH(Br_6.0), the results indicate extensive conversion of the polydiacetylene structure to a mixed polyacetylene structure.The observation of additional weak absorptions corresponding to butatrienic units suggests that the bromine-backbone interaction leads to localization of conjugation defects.