Synthesis of ferrocene-modified phenylazomethine dendrimers possessing redox switching

The phenylazomethine dendrimer (DPA) with amino groups at the terminal (end-amine dendrimer) was synthesized by the convergent method without protection from 4,4′-diamino-3,3′,5, 5′-tetramethylbenzophenone (DTB) as the raw material. The amino groups enabled the periphery of the dendrimer (DPA) to be modified by functional molecules, and we succeeded in the synthesis of the end-ferrocene dendrimer (A), which was perfectly modified by the ferrocenes, in one step with high yields. The stepwise metal complexation from the core was also observed in A G2 and A G3. The equilibrium constant K of the terminal imine connected with ferrocnes was determined to be 10 times smaller than that of the N-diphenylmethylene imine (ca. 10⁵ [M^-1]); however, it was strong enough for metal assembling. We found that A G3 showed redox switching by the addition of metal ions. The potential jump of the modified ferrocenes from 0.32 to 0.42 V was observed, when the complexation of Fecl₃, which started from the first layer, reached the third-layer imines next to the ferrocenes. This behavior was reversible based on the encapsulation reversibility and releasing of iron ions.