Proton-Coupled Electron Transfer (PCET) is an important mechanistic motif in chemistry that allows for efficient charge transport in many biological systems. We seek to understand how the proton and electron motions are coupled. We prepared a bidirectional system that allows us to independently tune the system's kinetic and thermodynamic parameters. The target of interest is a biomimetic heme system, which will allow for a detailed mechanistic study of the formation of the oxidation states of heme cofactors, particularly Fe(IV). The bidirectional model is prepared using a hangman porphyrin with an axially coordinated metal center, and the electron transfer event is triggered by excitation of the porphyrin. To understand the signatures of different electron acceptors and binding to the metal center, a redox inactive zinc porphyrin is used to allow for longer excited state lifetimes and well known transient signatures. Three diimide acceptors have been coordinated through a pyridine ring to the metal center of the porphyrin, and electron transfer was triggered both by excitation of the porphyrin and the acceptor. Lifetimes of the charge separated state were determined using picosecond and nanosecond transient absorption. Synthesis of the systems and spectroscopic data are presented.

Photoinduced charge transfer between porphyrins and axially bound diimide acceptors

243rd National Meeting (2012)

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