We use molecular dynamics to investigate the instantaneous structure of a fourth generation (dansyl terminated) dendrimer of propylene amine dissolved in CH2Cl2, and of the same system upon the subsequent encapsulation of several eosin Y dyes. Calculations, in a cubic box with up to similar to3500 solvent molecules and a maximum of 12 eosins, show that one of the effects of the presence of the guest molecules is to "close" the structure of the box where they are contained. Multiple entrances-exits of the guest molecules in the dendrimer are observed in less than a nanosecond, until the excess eosins are irreversibly expelled and their number is finally brought down to the experimental limit of 6. The guest molecules are distributed at two main distances from the center of the dendrimer and their surroundings are far from static. Eosins move inside the hyperbranched molecule in a way similar to what the solvent molecules do and sometimes aggregate.