The effect of temperature on the internal dynamics of dansylated POPAM dendrimers

The internal and rotational dynamics of the dansylated poly(propylene amine) dendrimers (POPAM) have been studied by time correlated single photon counting (TCSPC) and molecular dynamics (MD) simulations. The hydrodynamic volumes of the dendrimer generations from G1 to G4 were estimated by fluorescence anisotropy data. Experiments and simulations suggest that the volume and the shape of the dendrimers are temperature dependent. At low temperatures the dendrimer structure becomes more spacious and rigid and back-folding of the individual branches is slowed down. For the G3 and G4 generations the temperature effects are much stronger than for the smaller G1 and G2 generations, where back-folding does not play a significant role. MD simulations elucidate the temperature-driven contraction, which is governed by the balance between intra-dendrimer and short-range solvent-dendrimer interactions and is further tuned by the dependence on the dendrimer generation, functionalization, and solvent. These findings pave the way to the design of dendrimers with temperature-dependent volume, accessible area, and host-guest chemistry.