Photoinduced Energy and Electron Transfer Processes

Abstract This chapter introduces the supramolecular photochemistry, i.e. photochemistry applied to supramolecular systems, and discusses the thermodynamic and kinetic aspects of photoinduced energy and electron transfer processes both between molecules and within supramolecular systems. In the case of electron transfer processes, Marcus theory is presented as well as quantum mechanical theory. For energy transfer processes, coulombic and exchange mechanisms are illustrated and the role of the bridge in supramolecular structures is discussed. 

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When interaction between the metal-based components is weak, polynuclear transition metal complexes belong to the field of supramolecular chemistry. At the roots of supramolecular chemistry is the concept that supramolecular species have the potential to achieve much more elaborated tasks than simple molecular components while a molecular component can be involved in simple acts, supramolecular species can performIn other words, supramolecular species have the potentiality to behave as molecular devices. Particularly interesting molecular devices are those which use light to achieve their functions. Molecular devices which perform light-induced functions are called photochemical molecular devices (PMD). Luminescent and redox-active polynuclear complexes as those described in this chapter can play a role as PMDs operating by photoinduced energy and electron transfer processes. ... 

In the next example, a mixed SAM is discussed which aims to utilize photoinduced energy and electron transfer processes to create a photocurrent in an approach which is reminiscent of the natural photosynthetic process. Figure 5.33 illustrates the molecular structures of the components of interest, i.e. the molecular triad ferrocene-porphyrin-fullerene (Fc-P-C6o) and a boron dipyrrin thiol (BoDy) [67]. Mixed monolayers were generated by coadsorption onto vacuum-deposited gold... 

De Cola L, Belser P. Photoinduced energy and electron transfer processes in rigid bridged dinuclear Ro/Os complexes. Coord Chem Rev 1998 177 301-46. 

M. Guldi, et al., Molecular Engineering of C60 based oligomer ensembles Modulating the competition between photoinduced energy and electron transfer processes, J. Org. Chem. 67 (2002) 1141-1152. 

For a simple dinuclear compound D-S-A the photoinduced energy and electron transfer processes are represented schematically in Figure 3. 

Photoinduced Energy and Electron Transfer Process between Excited Sensitizer and Metal Nanocore... 

Figure 16. Photoinduced energy and electron transfer processes occurring in [2]rotaxane 18 + [81], which behaves as a triad for photoinduced charge separation according to the scheme illustrated in Figure 14a. For more details, see text.

Although the development of antenna-sensitizer devices for the spectral sensitization of semiconductors might have some practical impact, it would clearly be unrealistic to consider most of the work described in this article of direct relevance to photocatalysis. It seems likely, however, that the need for increasing efficiency and selectivity will lead towards the development of complex photocatalytic systems of supramolecular nature. Thus, further fundamental studies on ways to control and direct photoinduced energy and electron transfer processes in supramolecular systems seem to be worthwhile. 

The key step of the process is, of course, the unimolecular electron-(or energy-) transfer step (ke). Before going into more details (Sect. 2.2.3), it is important to extend our discussion to photoinduced energy and electron transfer processes in supramolecular systems where A does not need to diffuse to encounter B, but is already more or less close to B because A and B are linked together. 

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