Abstract
Crystals of 1,6-bis(3’,6’-dibromo-N-carbazolyl)2,4-hexadiyne (DCHBr4, 1a) belong to the monoclinic system, space group P2(1)/c, with a = 15.408(5) Angstrom, b = 4.120(1) Angstrom, c = 20.032(6) Angstrom, beta = 95,72-(3)degrees, V = 1265.3(11) Angstrom(3), and Z = 2. Full-matrix least-squares refinement of positional and displacement parameters for all atoms (H atoms fixed at calculated positions), with 1570 reflections (I > 1.96 sigma(I) led to R = 0.0469 and R(w) = 0.0448. The crystal structure of DCHBr4 consists of linear chains of molecules stacked along the crystallographic b axis with an orientation similar to that reported earlier for 1,6-di-N-carbazolyl-2,4-hexadiyne (DCH, 1b) at T < 142 K. Using the accepted structural criteria for solid-state reactivity in diacetylene monomers, DCHBr4 is predicted and found to be markedly less reactive to Co-60 gamma-rays, UV, and thermal treatment than the room-temperature form of DCH. Prolonged heating of DCHBr4 at T > 200 degrees C leads to solid-state polymerization of this monomer accompanied by thermal decomposition; 3,6-dibromocarbazole was identified as a volatile product of the latter process. The color change accompanying the solid-state polymerization of DCHBr4 suggests applications for this monomer as an irreversible thermochromic sensor. The product of the solid-state reaction is a poly(diacetylene), as determined from resonance Raman spectroscopic measurements.