Light-triggered electron transfer

Fig. 14 Light-triggered electron transfer, monitored by photomodulated amperometry.

The light-driven, energy- and electron-transfer processes trigger reactions that finally lead to the oxidation of water, the reduction of NADP+, and the build-up of a proton gradient across the photosynthetic membrane to produce ATP These processes are catalyzed by two membrane-embedded pigment-protein complexes, called... 

A feature that makes the reaction centre different from most other redox proteins is that light is used as a substrate by the complex, triggering the trans-membrane electron transfer reaction. As a result, the reaction centre has been at the forefront of research on biological electron transfer, and in particular has made a major contribution to the study of ultrafast, picosecond time-scale electron transfer. 

Light excitation of the bacterial reaction centre triggers a series of electron transfer reactions that, due to variations in distance between the cofac-... 

The comparatively poor thermal electron transfer reactivity of organosilanes has triggered fairly extensive and successful efforts to induce such reactions photolytically. Due to the transparence of most organosilanes, even with Si-Si bonds in the visible region, many such reactions were carried out using UV light... 

Light absorption modifies the driving force for electron transfer processes in all kinds of materials. As photoactivated species are always better oxidants and reductants than their ground state equivalents, an enhanced redox reactivity is usually observed in the excited state. Photoreactions are therefore ideally suited to trigger, study, and mimic bioinorganic electron transfer. 

This type of electron transfer reaction requires the presence of a donor-acceptor couple, and is triggered by light excitation on one of the two reaction partners. The species which absorbs the exciting light must possess appropriate photophysical properties such as a long-lived excited state at suitable energy. The quencher, on the other hand, must possess appropriate redox levels. 

The role played by MWCNTs is to provide electrons into the Ti02 condnction band under visible light irradiation and to trigger the formation of very reactive radicals snch as the snperoxide radical ion 0 . Back electron transfer from adsorbed OH closes the electrocatalytic cycle and provides a sonrce for the hydroxyl radical HO, which is responsible for the degradation of the organic molecnles (Fignre 13.2). 

The application of inexpensive photoactive copper complexes has given great impulse to visible light-mediated photoredox catalysis, e.g. for C-C and C-N coupling reactions. Irradiation of Cu-complexes both triggers metal centred single electron transfer processes and assists the Cu-catalysed elemental steps, in which the substrate is covalently bonded. Successful extension of cooperative copper photocatalysis to other reactions is expected for the near future. " ... 

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