Light induced processes in artificial reaction centers

This project is related to the following Fields, Subjects and Techniques:

Natural photosynthesis utilizes two coupled pigment systems, a light-harvesting antenna and a photochemical reaction center, for efficient conversion of light-energy into stabilized charges that is used to drive the conversion of solar energy into chemically stable high energy products. Both pigment systems are absolutely essential for the operation of photosynthesis. The reaction center converts short-lived excited state energy into stabilized charges, and without the light collection capacity of the antenna, the photosynthetic efficiency would be vanishingly low at the ambient light intensities delivered by the sun. The reaction center consists of a few (typically about 6) highly specialized pigment molecules, whose organization and interactions are fine tuned to optimize unidirectional electron transfer across the photosynthetic membrane, to achieve a long lived charge separated state with high efficiency. In oxygenic photosynthesis the oxidizing power of this charge-separated state is used to extract electrons from water, and form molecular oxygen, with the help of a catalytic manganese cluster.

The operational principle of an artificial photosynthetic system for light driven catalytic production of energy rich molecules is illustrated in Fig. 1.

Figure. 1. Light energy is collected by the antenna and transferred to the Reaction Center where charge separation occurs. The positive charge of the reaction center would drive a water splitting process via catalytic site 1, whereas electrons would be used to drive a reductive process in catalytic site 2, for instance producing methanol from carbon dioxide.

Figure 2 illustrates a multicomponent system for light induced electron transfer processes. Light absorption by the Ru-pyridyl moiety results in electron transfer to the aromatic groups, followed by fast electron transfer from the Mn-complex forming a long lived charge separated state. The electron transfer processes are studied by picosecond and nanosecond transient absorption spectroscopy. Time resolved X-ray spectroscopy would reveal optically dark processes and ligand dynamics within the Mn-complex.