Iridium-porphyrin systems

A number of iridium-porphyrin systems, including mononuclear and cofacial diporphyrins, have been adsorbed on pyrolytic edge-plane graphite electrodes and tested for their ability to reduce dioxygen to water (82). The original system investigated, [Ir(oep)H], where oep = 2,3,7,8,12,13,17,18-octaethylprophyrinato, was unique in that, while monomeric, the complex was still active in acidic solutions at potentials of +0.72 V vs NHE at pH 1 (82a). The [Ir(oep)H] did become inactive at potentials less than +0.2 V vs NHE, unlike the cofacial dicobalt diporphyrin systems. In the more recent report of these systems (82b),... 

Let us first consider the situation when porphyrin chromophores are excited. In this case, only electron transfers are possible within the triads, and also within the model dyads (not represented) used as reference compounds. Upon excitation of the iridium chromophore in the UV, an ET process to both porphyrins occurs. In these systems, it is interesting to note that the nature of the solvent used for the photophysical studies has a strong impact on the photoinduced processes and on the lifetimes of the CS states generated. These data are summarized in Figure 13.61 in the form of energy diagrams. 

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