Charge separation quantum yield

This probability decreases exponentially with time, approaching the charge separation quantum yield cp0 = fi(oo) = flout(oo). The relaxation to this limit normalized to a fraction of recombined ions, 1 — (p0, can be represented as follows ... 

A more complex situation arises with the charge separation quantum yield cp0. In the exponential model, this is... 

AGr = AGk(ct). Another question is, whether z/D can be considered as a ratio k-et/kseV, because neither of this rates exists in reality. Despite this fact, the free energy dependence inherent in z is attributed to Le,(AGr) in the vast majority of experimental works. This is why the later theories also present the charge separation quantum yield in the same way ... 

Figure 3.24. The charge separation quantum yield in polar solvents (rc — 0) as a function of the starting distance ro for the exponential recombination rate (Wc — 100ns 1, / — 1 A, o = 2.14x 1010m 1s 1) and the two diffusion coefficients Z)=10-4cm2/s (—) and D = 1(T8 cm2/s (—).

If excitation is weak or partner concentration is small, then the free ions are produced in low concentration and their bimolecular recombination is too slow to be seen in the timescale of the geminate reaction. Therefore the kinetics of the latter is often studied separately with a fast time-resolved technique. Alternatively, the free-ion quantum yield found from the initial concentration of ions participating in the slow bimolecular recombination can be used to calculate

free energy but of the solvent viscosity as well. These investigations were carried out on the following systems ... 

According to Eqs. (3.320) and (3.195), the averaged charge separation quantum yield is expressed through the mean recombination efficiency Z(AG,D,D) ... 

When the ionization is irreversible, tpa = 1, the charge separation quantum yield is equal to cpp, which becomes the share of RIPs that escaped geminate recombination into the ground state. In more general case, when the reverse electron transfer into the excited state can not be neglected, this is the fraction of ions that escaped any recombination, in either the ground or excited states. To clarify this point, let us illustrate it by an example of contact electron transfer. 

Here an important definition for the rate constant of free carrier production, k, is given. The latter differs from the ionization rate constant by a multiplier equal to the charge separation quantum yield tpm, obtained in the Markovian approximation. This difference indicates that the number of photogenerated ions that avoid geminate recombination and become free is less than their total amount, cpm < 1. 

Figure 3.58. Decay of the excited donor concentration (solid line) accompanied by ion accumulation/recombination (dashed line) and depletion of neutral acceptors (dotted line) at Wi = wr = 1000 ns-1 andrD = oo (the remaining parameters are the same as in Figs. 3.57 and 3.58). The shortest stage of excited donor decay is shown in the insert in comparison to the excitation decay without bimolecular recombination in the bulk (dashed-dotted line). The charge separation quantum yield (p = 6.2%,A (0) = 10-2M,c = 10-4M. (From Ref. 195.)...

However, the theory of exciplex dissociation cannot be made spinless like that for photoacids (Section V.D). The dissociation products are radical ions and the spin conversion in RIPs essentially affects

other quantities listed in Eq. (3.589). To illustrate this phenomenon, let us concentrate on the fluorescence yield, which is affected through %E(ks) and the charge separation quantum yield cp(cr). We will consider the general solution obtained for these two quantities in Ref. 31 only in the simplest case of highly polar solvents for which the Green functions are well known. 

In contrast, the Markovian theory leads to a much simpler picture—it cuts off the maximum related to the geminate process and underestimates essentially the charge separation quantum yield. This is a consequence of the full ignorance of... 

Inspired by previous rotaxane assemblies, Ito and Tanaka have reported the synthesis and the properties of triad 130 incorporating two zinc porphyrins and a mechanically attached Ceo electron acceptor. The behavior of the assembly depicted in Figure 13.70 is impressive in terms of lifetime of the CS state. The charge separation quantum yield is efficient (95%), and excitation of the zinc porphyrins leads to an eT process from their first singlet excited state of ZnP to... 

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