Ion dissociation in non-polar solvents is still far from being fully understood. Usually it is studied with surfactants which aggregate and form micelles. Here, we report on experiments with dendrimers, where the structure is defined with atomic precision. The ion dissociation and transport properties of a series of tetrabutylammonium salts (TBAþ) of rigidly dendronized anions with various sizes have been investigated in toluene, THF, and chloroform for a range of concentrations with dielectric spectroscopy and diffusion ordered spectroscopy (DOSY)-NMR. This is one of the first cases that one can study salts in low polarity solvents. The new synthetic approach increases the solubility and allows for investigation of both steric hindrance as well as electronic effects in producing weakly coordinating anions. We found that steric effects promote ion dissociation. In addition, fluorine substitution in the dendritic corona screens the electrostatic interactions and leads to increased dissociation. From the degree of dissociation and the measured diffusion coefficients, the free anion and cation diffusion coefficients were extracted and compared for the different dendrimer generations.
butt@mpip-mainz.mpg.de
