Intramolecular photochemical electron transfer in a linked porphyrin-quinone molecule as a model for the primary step of photosynthesis

The primary photochemical process in algal and green-plant photosynthesis is a one-electron transfer reaction from a chlorophyll donor species to an electron-acceptor molecule, with the electron transfer taking place across the thylakoid membrane probably within a special reaction-centre protein 1 . A similar process takes place in bacterial photosynthesis. We have mimicked this reaction through the synthesis described here using the method of Kong and Loach 2 , of a single molecule (P–Q) (I) containing a porphyrin (P) linked to a quinone (Q) by a hydrocarbon chain. When illuminated with visible light an intramolecular electron transfer occurs from the porphyrin to the quinone creating the biradical P ∔ –Q ⨪ . which can be detected by electron paramagnetic resonance (EPR) spectroscopy. In certain conditions the electron transfer is reversible.