Structural investigation of polydiacetylenes: A variable temperature solid state13C CP/MAS NMR study

The spectral features in the solid state13C CP/MAS NMR of poly (1,1,6,6-tetraphenylhexadiyn diamine) (poly(THD)) are compared with X-ray diffraction. The NMR data suggests that acetylenic carbons are nonequivalent in the unit cell resulting in two resonances. On the other hand, a single acetylenic carbon resonance was observed for poly (1,6-di-N-carbozolyl-2,4-hexadiyne) (poly(DCH)). The orientation of side groups in the crystal structures of poly(DCH) and poly(THD) are responsible for equivalence and nonequivalence of acetylenic carbons. The structural changes due to thermochromic transitions are monitored by variable temperature solid state NMR. The solid state VT NMR data suggest that the backbone and side chain conformations of blue phase and red phases of poly(bis-n-propyl urethane of 5,7-dodecadin-1,12-diol) (poly(PUDO)) are distinctly different. For the first time, we present a solid state NMR spectrum showing the presence of both the blue and red phases of this polymer at the thermochromic transition temperature (ca. 115–125°C).