Effects of rotational symmetry order on the solid state dynamics of phenylene and diamantane rotators

The rotational dynamics of phenylene and diamantane rotators in crystals of 1,9-bis(4-[3,3,3-triphenylpropynyl]phenyl)diamantane were analyzed independently within the same crystal structure. The dynamics of phenylene rotation were established by dynamic line shape analysis using 13C CPMAS NMR. The phenylene signals were selectively highlighted by deuteration of the aromatic trityls and the use of short contact times for cross polarization. The dynamics of the diamantane group were established by 1H spin-lattice relaxation under conditions where dipolar relaxation was shown to be the dominant mechanism between 250 and 425 K. A factor of 20 000 between the rates of rotation of the faster diamantane and the slower phenylene at 300 K supports expectations that higher symmetry rotors should have significantly faster dynamics.