C-13 CPMAS NMR of 5,10,15,20-tetrakis (4-n-dodecylphenyl)porphyrin: dynamics of aliphatic chains in discotic lamellar mesophases

Solid state C-13 CPMAS NMR spectra of 5,10,15,20-tetrakis(4-n-dodecylphenyl )porphyrin (C12TPP) have been studied to elucidate the microscopic structur es and dynamics in the mesophases. The temperature dependence of C-13 CPMAS NMR in the aliphatic regions is discussed mainly in relation to the phase transitions. The spectra for the aliphatic chains showed remarkable changes with the phase transition from crystal to lower mesophase (Mt) and from lo wer to higher mesophase (M-L). It was found that the aliphatic chains parti ally melt in the M-L' phase, while they melt totally in the M-L phase. The spectra in the aromatic region did not vary greatly with the transitions fr om crystal to M-L' and from M-L' to M-L, which probably means that the mole cular D-4h symmetries are distorted in these mesophases, as in the crystal, on the time scale observed by NMR (similar to kHz).