Studies of azo-hydrazone tautomerism and H-bonding in azo-functionalized dendrimers and model compounds

A C-13 NMR and UV-visible study of the tautomeric behaviour of azo-functionalized PAMAM (polyamidoamine) dendrimers and the corresponding model compounds in a variety of solvents is reported. Results of these studies indicate that the azo-functionalized PAMAM dendrimers exist as an equilibrium mixture of azo and hydrazone tautomers. A comparison of the behaviour of the dendnmers with model compounds suggests that the dendrimer periphery affects the tautomeric equilibrium between the azo and the hydrazone forms. The results further show that the proportion of the azo tautomer increases with dendrimer generation as well as in the presence of hydrogen-bond donor solvents such as acetic acid and 2,2,2-trifluoroethanol. Results of MO calculations suggest that the more planar azo tautomer would be favored because it stacks better on the dendrimer surface, which is consistent with experimental results. (C) 2002 Published by Elsevier Science Ltd.