Photoinduced electron transfer artificial photosynthetic systems

Significant progress in the development of such artificial photosynthetic systems, particularly aimed at the photolysis of water, has been reported in recent years. Several approaches to resolve the problems involved in controlling the photoinduced electron transfer process as well as the development of catalysts for multi-electron fixation processes will be discussed in this paper. 

The photoinduced electron transfer described above has been extended to photochemical H2 and O2 evolution to investigate half-reactions for water reduction and oxidation to use for artificial photosynthetic system in the future. These model reactions are represented by Figs. 13-13 and 13-14 in which so-called sacrificial electron donors (such as EDTA and triethanolamine) and acceptors (such as K2S2O8 and [Co(NH3)5Cl] ) are used, respectively. 

The photocatalytic properties and electron/photon-induced processes related to natural systems treated in Chapters 13 and 14 have been researched in depth. Different single fundamental multi-electron catalytic processes and photoexcited state electron-transfer reactions, both in polymer matrixes, are described in relation to photosynthesis (Section 13.2). It is now necessary to combine these reactions step by step to produce artificial photosynthetic systems. Some photoinduced energy-transfer processes (photooxidations) have now reached the level of practical application for wastewater cleaning (Section 13.4) and should be extended to other reactions induced by irradiation with visible light. 

The simplest supramolecular species capable of performing such type of process are covalently-linked three-component systems ("triads"). Two possible schemes for charge separating triads are shown in Fig. 5. Although the scheme in Fig. 5b is reminiscent of the natural photosynthetic reaction center, that of Fig. 5a seems to be more popular in the field of artificial triad systems. The functioning principles are shown in an orbital-type energy diagram in the lower part of Fig. 5. In both cases, excitation of a chromophoric component (1) is followed by a primary photoinduced electron transfer to a primary acceptor (2). This is followed by a secondary thermal electron transfer process (3) electron transifer from a donor component to the oxidized chromophoric component (case a), or electron transfer from the primary acceptor to a secondary acceptor component (case b). The primary process competes with excited-state... 

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