Metal-organic nanocages are discrete nanoporous structures that are promising for applications in sensing, drug delivery, light harvesting, electronic materials, and catalysis. Redox activity is potentially important for many of these uses, but the electrochemistry of these nanomaterials is underdeveloped in comparison to their other chemical and physical properties (e.g. host-guest, photophysical). Even fundamental electrochemical considerations, such as stability windows or the extent of communication between multiple redox-active units, have not been characterized for many cages. To better develop the electrochemistry of these nanomaterials, we sought to prepare examples whose structures (and solubilities) are maintained in multiple redox states, thereby facilitating detailed electrochemical studies. New porphyrin-based nanocages with [(NN)Pt]2+ linkers (NN = chelating N-donor ligands) were targeted because porphyrins exhibit rich and useful redox behavior, and the Pt complexes were expected to provide good stability. We successfully prepared trigonal prismatic cages comprising three tetrakis(3-pyridyl)porphyrin walls linked by six [(NN)Pt]2+ vertices (NN = ethylenediamine (en), TMEDA, and 2,2′-bipy), and characterized these cages by cyclic voltammetry, EPR spectroscopy, UV-vis-NIR spectroelectrochemistry, and stoichiometric chemical redox experiments. The Pt-based linkers provided sufficient stability for accessing singly and doubly reduced states of the porphyrins in each structure, enabling the effects of the different Pt linkers to be compared. Most notably, the [(2,2′-bipy)Pt]2+ linkers are redox-active within a similar potential range to the porphyrins, and the electron-accepting ability of these vertices was found to provide a stabilizing effect to the cage structure. These results elucidate useful principles for designing robust redox-active nanocages for electrochemical applications. The preparation of related nanocages of different shapes/sizes, the insertion of redox-active metals into the porphyrin walls of the cages, and potential catalytic applications will also be described.

Tuning the redox properties of porphyrin-based nanocages for electrochemical applications

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.