Direct charge transfer

Chemical reactions, which involve direct charge transfer between the metal atom in the lattice of the metal and the oxidising species. 

Fig. 3 Transient spectra obtained upon the application of a 200-fs laser pulse to a solution of stilbene (S) and chloranil (Q) in dioxane. (a) The fast decay ( 20 ps) of the contact ion-radical pair S+ , Q generated by direct charge-transfer excitation (CT path), (b) The slow growth ( 1.6 ns) of the ion pair S+ Q due to the diffusional quenching of triplet chloranil (A path) as described in Scheme 13. Reproduced with permission from Ref. 55.

Thus hole or electron transfer can follow a number of pathways across the semiconductor/electrolyte interface. First, one can have direct oxidative or reductive charge transfer to solution species resulting in desired product formation. Second, one can have direct charge transfer resulting in surface modification, such as oxide film growth on GaP or CdS in aqueous PECs. Finally, one can have photoemission of electrons or holes directly into the electrolyte. All of these processes provide some information about the electronic structure of the interface. 

The direct charge transfer to dichloroacetate proposed in reaction (7.21) requires that the scavenging molecules are adsorbed on the Ti02 surface prior to the adsorption of the photon. Otherwise, this reaction could not compete with the normal hole-trapping reactions (7.9) and (7.10). So the adsorption of the model compound DCA on the titanium dioxide surface prior to the bandgap excitation appears to be a prerequisite for an efficient hole scavenging. 

C. Conducting Composites Formed by Direct Charge-Transfer Reaction Between Two Solid Components... 

There are two methods of electrochcmically reducing acetylenes, namely, direct charge transfer to the triple bond from the cathode and the electrolytic generation of an intermediate which attacks the acetylene. The first method (direct reduction) has the advantage that mechanistic studies using, for example, cyclic voltammetry and coulometry can be carried out, while the second method (indirect reduction) appears to offer more scope for product control and has been more extensively investigated. 

The electron hopping pathway which Is the dominant pathway at thick films is an example of directed charge transfer just as in the bilayer experiment. The sense of the direction of electron transfer from outside the inner film to the electrode is also the same. However, there are differences between the processes, per-... 

Surface chemistry, in general, is an area in which the ability to selectively modify the chemical and physical properties of an interface is highly desirable. The synthetic chemistry of surfaces is now in a developing stage, particularly with respect to the attachment of electroactive redox sites to metal or semiconductor surfaces (L-3). Single component and bilayer (4) electroactive films have been a field of intense research activity since their applications are apparent in catalysis, solar energy conversion, directed charge transfer, electrochromic devices, and trace analysis. 

As shown by Tunesi and Anderson (48), the efficiency of the photoredox nrocess for organic compounds depends on their adsorption behavior. When direct charge transfer (inner-sphere complexes) occurs, this mechanism is more efficient than free radical attack. These authors interpret their results nth salicylate at low pH as a direct electron transfer from the adsorbed organic molecule—assumed to be an orbital configuration of the chelate ring— the semiconductor. 

In the thermal charge transfer methods the electron affinity of a molecule is determined by bracketing the electron affinity of a test species between that of two species with known electron affinities. When the reaction studied is AB —) + CD AB + CD(—) direct charge transfer, the relative electron affinities... 

The photo-induced charge conduction mechanism in double-strand guanine-rich DNA-based molecules, and AT pairs attenuating the conductivity by off-resonance superexchange steps is broadly supported. Mechanistic mapping has been based on both direct charge transfer kinetics in the nano-, pico- and femtosecond ranges... 

Direct charge transfer mechanisms such as that of equation (16) are also possible. You will immediately note, however, that the ionised species so-produced is that of an ion-radical, hence the same problem of stabdity noted previously for El conditions would apply. 

Most of the electrochemical processes studied in the last decade with substrates containing carbon-carbon triple bonds, were reductions. In many cases electrolytic generation of intermediates which attack the triple bond is involved rather than direct charge transfer. The latter requires the use of aprotic solvents, but isolated triple bonds generally are reduced/oxidized beyond the accessible potential range of the more common electrolytic solvents and only conveniently substituted alkynes may undergo direct electron transfer involving the triple bond. 

Some information also exists concerning the energetics of the coraplexation reaction. In particular, the cooperativlty of the iodine binding process has been accepted for many years (22, 23). Direct charge transfer interaction between iodine and the oxygen atoms of the polysaccharide annulus has been proposed (, 25),... 

S. Pal, E. C. Alocilja, and F. P. Downes, Nanowire labeled direct-charge transfer biosensor for detecting Bacillus species, Biosens. Bioelectron., 22, 2329-2336 (2007). 

The reactions leading to H (H20) in moist oxygen studied with the same apparatus and method are shown in Table III. This reaction sequence is more interesting and more complicated since the direct charge transfer... 

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