Dendrimer is a hyper-branched, sea urchin-shaped macromolecule that possesses multiple molecular cavities. Inclusion complexes formed between the nitroxide probe and the dendrimer were investigated with ESR spin probe technique. ESR spectral linewidths of the nitroxide probes with different hydrodynamic radius were monitored in the presence of the dendrimer to determine the probe's rotational correlation time (tau(R)). The agreement and disagreement with the order in the probe size and tau(R) was interpreted in terms of the probe-solvent-dendrimer intermolecular interaction. The activation volume Delta V-double dagger was determined from high pressure experiments and there were distinctive Delta V-double dagger inside dendritic boxes. (C) 2009 Elsevier B. V. All rights reserved.