The behavior of a fifth generation phosphorus dendrimer having a hydrophobic interior and hydrophilic end groups is studied in solution in water using the pulsed-field gradient spin-echo NMR technique. Addition of THF to this solution induces dramatic changes concerning the size of the dendrimer (+150% in volume), T1 relaxation of THF, and viscosity. This dendrimer behaves like a highly singular nanotool, able both to modify its environment and to be modified by it.