Acceptor electron transfer

Current research aims at high efficiency PHB materials with both the high speed recording and high recording density that are required for future memory appHcations. To achieve this aim, donor—acceptor electron transfer (DA-ET) as the hole formation reaction is adopted (177). Novel PHB materials have been developed in which spectral holes can be burnt on sub- or nanosecond time scales in some D-A combinations (178). The type of hole formation can be controlled and changed between the one-photon type and the photon-gated two-photon type (179). 

We first consider outer sphere transfer (ET) reactions, e.g. D" + A -> D + A, a donor-acceptor electron transfer without significant coupled internal reorganization of the D and A species [27,29,30]. A hallmark of such reactions, which has been long appreciated [27], is that the reactive coordinate is itself a many-body collective solvent variable (and is not the coordinate of the electron itself)- In particular, if R and P stand for the reactant and product, then the reactive coordinate is... 

X-ray analysis reveals a sandwich structure for these semi-conducting materials of formula [M(dmb)2]TCNQ TCNQ° (N= 1, 1.5), the polymeric chains of M(dmb)2 + are separated by layers of TCNQ- and neutral TCNQ (i.e., mixed-valence TCNQ- layers). The latter layer is responsible for the conductivity. Since TCNQ is an electron acceptor, electron transfer from the polymer to the mixed valence TCNQ layer is also possible from the Cu(I) center to the TCNQ- TCNQ° layer. This photoinduced electron transfer from... 

The role of mediator molecules in donor-acceptor electron transfer processes is an item of considerable recent interest [73 — 81]. A lot of research has been done on intermediate acceptors in the electron transfer in photosynthesis and theoretical studies bases on the superexchange interaction have been carried out [76 — 82]. In Refs. [83,84], electron transfer in the presence of ordered mediator molecules with arbitrary energy levels in one-dimensional case [83] as well as electron transfer in the presence of one resonant mediator [84] were considered. 

The cr-radical (III) and 02 are considered to be formed by electron transfer from the skatole anion to oxygen in the ternary complex (II), which is composed of a strong electron donor and a weak electron acceptor through Fe(II)-porphyrin (see Reaction 4). In such a complex (D-Fe(II)P-A type complex, D = electron donor, A = electron acceptor), electron transfer from the donor to the acceptor should occur more easily than the direct electron transfer in D-A complex, because in the former the cooperative interaction of the three components should decrease the energy barrier of the electron transfer. 

Marcus has recently returned to this problem [133] and, by analogy with the problem of donor-acceptor electron transfer at the interface between two immiscible liquids, has derived the following expression for ka, the heterogeneous rate constant for electron transfer from a semiconductor to a species in a contacting electrolyte ... 

Figure 7. State diagram for a sequential donor-to-bridge-to-acceptor electron transfer (wire-like behavior).

Figure 19. Two types of triads for photoinduced charge separation. Molecular components are designated as P (chromophore) D (donor) A (acceptor) A (secondary acceptor). Electron transfer processes are designated as cs (primary PET) cr (primary charge recombination) cs (secondary charge separation) cr (final charge recombination),...

It has been noted (Strehmel et al, 1999) that the fluorescent dyes 1,1 -dimethyl-2,2 -carbocyanine iodide (QB) and /j-AQV-dimethylamino-styryl-2-ethylpyridinium salt (DASPI) may be used both to monitor the crosslinking process and to detect Tg. These dyes have twisted intmmolecular charge-transfer (TICT) states that are accessible from the first excited singlet state. Such TICT states may be considered to arise from intramolecular donor-acceptor electron transfer whereby the new state is stabilized in a geometry perpendicular to the original conformation (Figure 3.34). 

Photoredox reactions occur either via imermolecular or via intramolecular processes. The most general scheme of an intermolecular photoredox reaction (Rehm and Weller, 1970) is shown in reaction 1 A compound C undergoes a transition from the ground state to an electronically excited state by absorption of light, C - C. If such an excited compound encounters a reaction partner Q (either an electron donor or an electron acceptor), electron transfer may take place, leading to C+ and Q ... 

In particular, Russell and co-workers (37) have made extensive ESR studies on electron transfer from carbanions and nitranions to various acceptors including azobenzenes, diaryl ketones, and nitroaromatics. Some one-electron transfer processes have been investigated using a combination of electrochemical and ESR techniques (26). In these experiments, radical anions were produced electrochemically and introduced into a mixing chamber containing an aromatic electron acceptor. Electron transfer was indicated by the formation of the ESR spectrum of the resultant radical anion. It was verified that the direction of transfer between two reactants could be predicted from E0f values derived from polarographic data. 

E. G. Petrov, Role of Polypeptide Chain Structure in Donor-Acceptor Electron Transfer through Proteins, Studia Biophysica 93, 237-240 (1983). 

P 9 run when the intervening medium is a molecular hnk between donor and acceptor. Electron transfer between protein-bound cofactors can occur at distances of up to about 2.0 run, a long distance on a molecular scale, corresponding to about 20 carbon atoms, with the protein providing an intervening medium between donor and acceptor. 

Carbon tetrabromide and methylviologen show particularly high reactivity toward singlet-excited DBO, with rate constants close to diffusion control. Clearly, photoinduced electron transfer to the quencher under photooxidation of DBO is responsible, which has been described recently for DBO and derivatives [197]. In contrast to its rather unfavorable electrochemical reduction potential, DBO is a good electron donor [198]. In combination with a strong electron acceptor, electron transfer becomes feasible. Blackstock and Kochi reported about ground-state charge-transfer complexes between DBO and carbon tetrabromide [123]. This is in line with the involvement of photoinduced electron transfer in the case of carbon tetrabromide. 

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