Stability of hydrogen bonds upon polymerization and color transition of diacetylenes: An FTIR spectroscopy study

FTIR spectra (400–7500 cm−1) have been recorded for polycrystalline films and single crystals of the diacetylene 4BCMU in the monomer, blue and red polymer states, and of 3BCMU monomer. Particular attention was paid to the amide bands associated to the urethanes in the side groups, which form one-dimensional H-bond linear chains quite similar to those found in peptides and proteins. The positions and strengths of these absorptions are practically unchanged by polymerization or blue to red polymer color transition. This suggests that the H-bond linear chains are the main constitutive interactions in these crystals, and that the conjugated parts must and do “adapt” to the unchanged H-bond lines. No evidence of side group disordering was observed at the irreversible blue to red transition in poly-4BCMU crystal.