Five generations of nitroxyl-functionalized dendrimers

The prepn. and ESR spectroscopy of a series of fully functionalized poly(propylenimine) dendrimers (DAB-dendr-(NH2)n; n = 2, 4, 8, 16, 32, 64) with 3-carboxy-PROXYL radical end groups is described. The pendant nitroxyl end groups exhibit a strong exchange interaction. As a consequence, the ESR spectrum directly reveals the no. of end groups from the splitting between the hyperfine transitions for the lower generations. For the higher generations an increasingly exchanged-narrowed ESR spectrum is obsd. The temp. and solvent dependency of the exchange interaction is used to assess the dynamic behavior of the dendritic branches. FT-IR spectroscopy shows that a hydrogen-bonded network between the amide functionalities is present, consistent with the obsd. solvent effect on the ESR spectra