Charge separation process

The successful design of both natural and artificial molecular photovoltaic devices rests on meeting three fundamental requirements, namely 121 (1) The quantum yield for the charge separation process should be as high as possible. That is, kcs > kd (Figure 1). (2) The lifetime, tcr (= 1 lkcr), of the CS state must be sufficiently long to enable it to carry out... 

Figure 1. Energy diagram illustrating the possible pathways available in a photoinduced charge separation process between a donor (D) and acceptor (A).

In general, these oxides show excellent optical quality including high transparency in the visible region that allows fluorescence as well as charge separation processes. Applications are numerous and range from... 

Temperature Dependence of the Kinetics. In an earlier article (22) we gave a detailed analysis of the temperature dependence of the rate of electron transfer from 1 (BPh ) to Q (Figure 4). Here we summarize some of the important considerations and discuss further the possible insights that the temperature and detection-wavelength dependence of the kinetics may give into the molecular mechanism of electron transfer and the overall charge separation process. 

Polar analytes can also form adducts with various ions. A typical adduct ion that is formed in the positive ion mode is [M + nNaJ L but many other adduct ions with K+, NHJ, CL, acetate are frequently observed (Figure 8.4). Their formation normally occurs in the bulk solution before the charge separation process, in the electrospray droplets during evaporation, or in the gas phase. If the analyte is weakly basic or polar, salts bearing cations may be intentionally added to the sample to stimulate the formation of positive ions [10,11]. 

Fig. 9 Illustration highlighting the possible importance of entropy in the charge separation process. Positive and negative polarons experience a strong coulombic attraction that may be offset by entropy to achieve charge separation. Reproduced with permission from [54]. Copyright 2010 American Chemical Society...

The last group of dyads considered here are those that incorporate TTFs in their structure. TTFs are powerful organic donors, which, when linked to the fullerene core and engaged in charge-separation processes, gain rather than lose aromaticity [128]. The modification of the donor strength on the TTF moiety in dyads (31a-c) allows the tuning of the... 

EPR is the method of choice to study the paramagnetic intermediates occurring in the light-induced charge separation process in the reaction centres of plants and photosynthetic bacteria2. Furthermore, other paramagnetic species in particular metal centres - that participate in the photosynthetic processes can be detected and characterized by EPR. Examples are various cytochromes,... 

Radical Pair States. - So far we have discussed single radical-ions that occur in the charge-separation process and can be trapped under certain condition in bRC or can even be chemically generated. The initial light-induced charge separation creates radical pairs (RPs) that can be studied by time-resolved transient or pulse EPR ... 

The Primary Donor Triplet State iP7a0 If in the charge separation process electron-transfer in PS I beyond the first acceptor A0 is blocked by treatment with sodium dithionite at high pH and illumination, which reduces the iron-sulfur centres (F) and the quinone (A, the triplet state of the donor, 3P7ao, is obtained via radical-pair recombination from the triplet RP according to ... 

The interface model predicts that Vcx in a dye cell will not be limited by because does not control the charge-separation process. Rather than having large potential gradients at equilibrium, as in conventional cells, the DSSC has only small and relatively insignificant values of and xbl. Illumination of a DSSC causes the potential gradients to increase, whereas in a conventional cell, they decrease upon illumination. Because the photoinduced increase in is practically eliminated by electrolyte ion redistribution, the photoinduced increase in p,neq can drive an efficient photoconversion process. 

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