Water-soluble azobenzene dendrimers

Water-soluble azobenzene-cored dendrimers 4–6 were synthesized as potential photoresponsive micelles to which the aggregation is triggered by photoirradiation. In the absorption spectra, the π–π∗ absorption band of the dendrimers largely blue-shifted with increasing the generation due to the shielding effect of surrounding dendron on the interaction between the core azobenzene and solvent water. Not only the surrounding dendron groups suppressed the E-to-Z photoisomerization, but also the rate of thermal Z-to-E isomerization depended on the generation of the dendrimer. Furthermore, we have observed a novel temperature dependence of the rate constant of the thermal isomerization.