Dynamic NMR of 1-phenylethynyl-3,5-bis(pentaphenylphenyl) benzene (1) and 1, 3,5 -tris(pentaphenylphenyl) benzene (2) allows us to determine two rotational barriers for each compound. For 1, a first process exhibits Delta G(double dagger) = 39.2 U/mol followed by a second one with a Delta G(double dagger) value of 69.9 U/mol. Two processes with similar rotational barriers are found for 2 (70.9 and 75.3 kJ/mol). Motional processes which can be related to these barriers are 60 degrees and 180 degrees rotations of the pentaphenylphenyl units about the single bond with the core benzene ring and rotation of the terminal phenyl rings of the pentaphenylphenyl units. The results are discussed considering the consequences of these processes on the NMR spectra. (c) 2007 Elsevier Ltd. All rights reserved.