Self-Assembled Molecular Rafts at Liquid|Liquid Interfaces for Four-Electron Oxygen Reduction

The self-assembly of the oppositely charged water-soluble porphyrins, cobalt tetramethylpyridinium porphyrin (CoTMPyP4+) and cobalt tetrasulphonatophenyl porphyrin (CoTPPS4–), at the interface with an organic solvent to form molecular “rafts”, provides an excellent catalyst to perform the interfacial four-electron reduction of oxygen by lipophilic electron donors such as tetrathiafulvalene (TTF). The catalytic activity and selectivity of the self-assembled catalyst toward the four-electron pathway was found to be as good as that of the Pacman type cofacial cobalt porphyrins. The assembly has been characterized by UV–visible spectroscopy, Surface Second Harmonic Generation, and Scanning Electron Microscopy. Density functional theory calculations confirm the possibility of formation of the catalytic CoTMPyP4+/ CoTPPS4– complex and its capability to bind oxygen.