摘要:
Giant redox dendrimers were synthesized with pentamethylcobalticinium termini for the fifth, sixth, and seventh generations (in addition to the nine-arm generation 0) up to a theoretical number of 3(9) tethers (seventh generation, G(7)). Therefore, a functional pentamethyl cobalticinium derivative was synthesized with a long arm. This tether-lengthening strategy was used as in the previously reported ferrocenyl and pentamethylferrocenyl series to overcome the bulk constraint at the periphery of short-tethered dendrimers. These polycationic cobalt-sandwich metallodendrimers were characterized by H-1, C-13, and Si-29 NMR, MALDI-TOF mass spectrometry (for generation 0), elemental analysis, UV-vis spectroscopy, dynamic light scattering (DLS), atomic force microscopy (AFM), and cyclic voltammetry. UV-vis spectroscopy and analytical data are consistent with a moderate amount of defects (G(5) and G(6)) that largely increases for G7 (which contains 14 000 +/- 1000 pentamethylcobalticinium termini). Cyclic voltammetry reveals full chemical and electrochemical reversibility for the cathodic reduction [dendr-(C5H4CoCp)-Cp-III*](+) -> [dendr-(C5H4COCp)-Cp-III*] up to G(7) as in the iron-sandwich series, showing that electron transfer is fast among the flexible peripheral redox sites.