Pyrene/dimethylaniline electron

This may not be the full answer as the photoinduced electron exchange between pyrene, P, and dimethylaniline, D, on CTAB micelles and other CTAB structures, etc.,... 

They studied the pyrene/3,5-dimethoxy-7V,N-dimethylaniline combination in methanol. After the initial laser flash, fast electron transfer occurs resulting first in... 

In reaction (2-2a), the electron transfer reaction occurs from Si of pyrene to N,N-dimethylaniline, giving a singlet radical ion pair involving the pyrene anion and N,N-dimethylaniline cation radicals. In reaction (2-2b), the electron transfer reaction occurs from... 

Lastly, electron transfer in D—[H]—A assemblies is not a perquisite of the excited states of metal complexes. Organic ensembles 38 and 39 (R = SiMe2 Bu), containing a dimethylaniline-anthracene redox pair, have been synthesized recently [124]. Preliminary time-resolved and steady-state fluorescence experiments indicate the occurrence of photoinduced electron transfer. In work related to Watson Crick base-paired systems, the excited state of the fluorescent pyrene derivative 40 is efficiently quenched (94-99 %) by 2 -deoxyguanosine (dG), 2 -deoxycytidine (dC), or 2 -deoxythymidine (dT) in aqueous solution [125]. A PCET mechanism is thought to be responsible for this process, as the thermodynamics of electron transfer are unfavorable unless coupled to a rapid proton-transfer step. The quenched lifetime of 40 in the presence of dC and dT in H2O is significantly extended by a factor of 1.5-2.0 in D2O this isotope effect is similar to that observed in the kinetics studies of 1 [70]. The invoked PCET reaction mechanism also accounts for the inability of dC and dT to quench the fluorescence of 40 in the aprotic organic solvent DMSO. 

Quantitative approaches to describing reactions in micelles differ markedly from treatments of reactions in homogeneous solution primarily because discrete statistical distributions of reactants among the micelles must be used in place of conventional concentrations [74], Further, the kinetic approach for bimolecular reactions will depend on how the reactants partition between micelles and bulk solution, and where they are located within the microphase region. Distinct microphase environments have been sensed by NMR spectrometry for hydrophobic molecules such as pyrene, cyclohexane and isopropylbenzene, which are thought to lie within a hydrophobic core , and less hydrophobic molecules such as nitrobenzene and N,N-dimethylaniline, which are preferentially located at the micelle-water interface [75]. Despite these complexities, relatively simple kinetic equations for electron-transfer reactions can be derived for cases where both donors and acceptors are uniformly distributed inside the micelle or on its surface. 

However, our concern is with the cationic surface which promotes a rapid exchange of an electron from dimethylaniline to pyrene, and thereafter maintains a long-lived ion which can react with further solutes added to the system. Hie concept of the experiment is, that dimethylaniline transfers the electron rapidly to pyrene via a diffusion controlled reaction, which occurs by movement of the reactants on the surface of the micelle until they encounter each other. Electron transfer then occurs, and the back reaction of the two ions is prevented by the surface of the micelle, which holds the reactants in an unsuitable configuration for back reaction to occur. However, the repulsive positive force of the micelle on the dimethylaniline cation rapidly drives it away from the micelle, and effective and efficient charge separation is achieved, with a quantum yield Q of unity for the process of charge separation. 

Figure 1. Electron transfer processes of pyrene (P) with dimethylaniline (DMA).

Table I shows the effect of various systems such as micelles, swollen micelles (achieved by adding hexanol to CTAB), microemulsion systems, vesicles formed from a double-chain CTAB surfactant, and reversed micelles with water cores formed with benzyl dimethylcetylammonium bromide in benzene. Hie active chromophore exists either as pyrene, pyrene sulfonic acid or pyrene tetrasulfonlc acid. Essentially the concept here is that the polar derivatives of pyrene will always locate pyrene at the surface of the micelle as these anionic species of pyrene complex with the positively charged surface. Dimethylaniline is used as an electron donor in each case, it can be seen that for pyrene, a continual decrease in the yield of the pyrene anion (ion yield of unity in the micelle) is observed on going from micelle to swollen micelle, to microemulsion, and no yield of ions is observed in a reversed micelle system. With pyrene tetrasulfonic acid the yield of ions over the different systems is fairly constant, even across to the reverse micellar system. However, the lifetime of the ions is extremely short in the reversed micellar system. An explanation for such behavior can be given as follows as we transverse across the...

Figure 9.17 Distance-dependence of in some donor-acceptor molecules. Plots of log( et) edge-to-edge distances in a variety of linked donor-acceptor systems, (a) Forward(D) and reverse (x) electron-transfer rate constants for zinc porphyrin-anthraquinone compounds in butyronitrile. (b) Forward ( ) and reverse (x) electron-transfer rate constants for dimethoxynaphthalene-dicyanoethylene compounds in benzene, compared with the forward rate constants for three anthracene-dimethylaniline systems (V) and four analogous pyrene-dimethylaniline molecules (-I-), all in acetonitrile. From J.S. Connolly and J.R. Bolton, in Ref. [21,e, p. 322].

Other examples of electron transfer reactions in surfactant assemblies are those between pyrene and dimethylaniline in micelles, between viologen derivative and zinc porphyrin as an electron relay, and between chlorophyll a and methylviologen in microemulsions the photoinduced reduction of duroquinone by zinc porphyrin in micellar solution the photoinduced redox reaction of proflavine in aqueous and micellar solutions retardation of back reactions in micellar systems light-driven electron transfer from tetrathiafulvalene to porphyrin and tris a, a -bipyridine)... 

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