Light-induced energy transfer

The light-induced energy transfer between adsorbed organic dyes, single nucleotides, and polynucleotides on the one hand, and ZnS/CdS templates on the other hand, has been intensively studied [242-244,247,328]. In one case at least, it has been quantified that an organic dye fac tris(2-phenylpyridine) iridium, when adsorbed on a ZnS surface, can serve as an antenna and increase the amount of quanta captured by ZnS [329]. This result supports the possibility of a positive feedback between the number of UV-light-absorbing zymes in a ZnS compartment and the yield of photosynthetically produced metabolites. 

The theoretical treatment [12.38] shows that for dipole-dipole interaction the maximum cross section for light-induced energy transfer occurs at a laser wavelength Xj such that energy conservation is satisfied for the infinitely separated atoms. This implies for the situation in Fig.12.19 that... 

Figure 1. Potential energy plot of the reactants (precursor complex) and products (successor complex) as a function of nuclear configuration Eth is the barrier for the thermal electron transfer, Eop is the energy for the light-induced electron transfer, and 2HAB is equal to the splitting at the intersection of the surfaces, where HAB is the electronic coupling matrix element. Note that HAB << Eth in the classical model. The circles indicate the relative nuclear configurations of the two reactants of charges +2 and +5 in the precursor complex, optically excited precursor complex, activated complex, and successor complex.

This article is intended to review the published work on the photochemistry and photophysics of osmium complexes that has appeared in the literature over the past several years. We have attempted to cover, albeit somewhat selectively, literature dating back to the year 2000. A variety of reviews pertaining to particular aspects of osmium photophysics and photochemistry were published prior to 2000. A few reviews discuss the photophysical behavior of primarily monometallic Os complexes in solution [1,2]. Several earlier reviews discuss light induced energy and electron transfer reactions involving osmium complexes in much of this work the Os complex is not the chro-mophore [3-6]. Finally, one review exists discussing the photochemistry of Os carbonyl complexes [7]. 

Photosynthesis is the inspiration for all efforts to harvest solar energy ranging from solar cells to light-induced water splitting. Historically, synthetic molecular systems that undergo light-induced electron transfer reactions have featured prominently in efforts to functionally mimic photosynthesis.Like the natural system, many of the intermediates and transient products of these light-induced electron transfer reactions are radicals thus, they are subject to spin-chemical effects. 

The energy of the light-induced charge-transfer transition in a symmetrical doublewell system is given by Eq. 39 [29, 30]. 

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