Characterization of two series of nitrogen-containing dendrimers by natural abundance 15N NMR.

Two series of small generation dendrimers built with phosphorus atoms at each branching point and various types of nitrogen atoms at natural abundance of (15)N within the branches are characterized by a gradient enhanced GHNMQC (gradient hydrogen-nitrogen multiple quantum coherence) (1)H-(15)N NMR technique. The first series contains two types of nitrogen atoms, included in phosphorhydrazone linkages (CH=NNMe-P(S)), whereas the second series contains four types of nitrogen atoms included in azobenzene linkages (Ar-N=N-Ar') in addition to the phosphorhydrazone. The influence of the trans/cis isomerization of the azo bond on the (15)N NMR has also been studied. Despite the low solubility of the azobenzene-containing dendrimers, which renders the detection of some signals difficult, (15)N NMR appears as a very sensitive tool to detect chemical changes in the dendritic structure.