Photon-induced electron transfer

Our work and that of Tench (24) has shown that the electron transfer sites on these metal oxides (e.g., MgO and CaO) are selective and yet present in high surface concentration. Preliminary activation by thermal or photochemical oxide means is required, however. This means that these processes can be related to photon-induced electron transfer (60, 61, 62, 63, 64) in semiconductor metal oxides in that similar surface sites may be required (i.e., similar coordination geometries). 

Chatterjee A, Suzuki T, Onodera Y, Tanaka DAP (2003) A density functional study to choose the best fluorophore for photon-induced electron-transfer (PET) sensors. Chem Eur J 9 3920-3929... 

In addition to MEF, Metal - Enhanced Phosphorescence (MEP) at low temperature (18,19) has also been reported, whereby non-radiative energy transfer is thought to occur from excited distal triplet-state luminophores to surface plasinons in non-continuous silver films, which in turn, radiate fluorophore/lumophore phosphorescence emission efficiently (Fig. 10.2-Middle). This observation suggests that photon-induced electronic excited states can both induce and couple to surface plasmons (mirror dipole effect) facilitating both enhanced S fluorescence and... 

The oxidized and reduced species are usually highly energetic, storing a substantial fraction of the energy absorbed from the photon. The charge separation that occurs in such a photo-induced electron transfer provides a way to convert the excitation energy of the excited molecule to a chemical potential in the form of a radical ion pair. 

An alternative inexpensive organic polymer-based photovoltaic solar cell has been invented. In this device, p-type and n-type semiconductors are sequentially stacked on top of each other. In such devices, absorption of a photon by a ji-conjugated polymer results in the formation of an excited state, where coulom-bicaUy bound electron-hole pair (exciton) is created. This exciton diffuses to a region of interface of n-type semiconductor where exciton dissociation takes place and transport of charge to the respective electrodes occurs. For example, the photo-induced electron transfer from a donor layer (p-type) to acceptor layer (n-type) takes place in a polymer/fullerene-based organic bilayer solar cell, MDMO-PPV PCBM, with power conversion efiiciency of 2.5 % (Fig. 11.8) [13]. 

Schemes 8 and 9 differ by whether the photosensitizer functions as the electron donor (Scheme 8) or acceptor (Scheme 9). In both cases, amplification of photons by a chain reaction is possible. The energetics of photosensitization by electron transfer have been discussed in Volume 4, Chapter 20, including a consideration of chain reactions. A comprehensive report on light-induced electron transfer reactions of unsaturated compounds, including dimerization, is available." ...

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