Introduction photoinduced electron

Until now, the isotopic effect was discnssed only in relation to the reactants. In electron-transfer reactions, the solvent plays an eqnally important role. As mentioned, different solvate forms are possible for reactants, transition states, and products. Therefore, it seems important to find a reaction where the kinetic effect resulting from the introduction of an isotope would be present for solvents, but absent for reactants. For a published work concerning this problem, refer Yusupov and Hairutdinov (1987). In this work, the authors studied photoinduced electron transfer from magnesium ethioporphyrin to chloroform followed by a dark recombination of ion-radicals in frozen alcohol solutions. It was determined that the deuteration of chloroform does not affect the rate of transfer, whereas deuteration of the solvent reduces it. The authors correlate these results with the participation of solvent vibrational modes in the manner of energy diffraction during electron transfer. 

In making rotaxanes usable as parts of molecular devices and with the purpose of studying long range election transfer processes within large molecular systems of well controlled geometries, the introduction of photoactive and electroactive compounds has been a valuable development. Photoinduced electron transfer between porphyrin species has a particular relevance to the primary events occurring in bacterial photosynthetic reaction center complexes, and so is a well studied phenomenon. 

A number of excellent reviews on the theoretical aspects of photoinduced electron transfer have appeared in the literature and the interested reader may refer to these original articles. Due to the fundamental importance of the electron transfer step for the title process and in order to facilitate reading this chapter a brief introduction on PET will be given [2,6]. 

Studies of the efficiency of quinone photochromism showed that the introduction of electron-donor substituents in the quinone cycle as well as the bulky substituents in the migratory group reduced the efficiency of the photoinduced para- ana-quinone rearrangement. At the same time, the introduction of electron-donor substituents in the migratory phenoxy group was favorable for photochromic transformations. On the contrary, the introduction of electron-acceptor substituents decreased the efficiency of the phototransformations. These experimental data agree well with the known concept of the photochromic transformations of these compounds as reversible intramolecular photoinduced substitutions. 

Decomposition of the photochromic compounds can occur because of the interaction between molecules of the photoinduced form and alcohols. This phenomenon is a consequence of the deficiency of the electron density on the carbon atom in the 9-position of the ana form for aryloxyanthraquinones.27 The reaction of nucleophilic 1,4-addition of alcohol molecules with molecules of 9-aryloxy-l,10-anthraquinones depended on the nature of the substituent.27 The introduction of electron-acceptor substituents enhanced and the electron-donor substituents reduced the rate constant. The electron-donor substituents contributed to the stability of the photoinduced 1,10-anthraquinones. This conclusion was supported by the data on the interaction between derivatives of 9-aryloxy-l, 10-anthraquinone, and aliphatic and aromatic amines.35... 

The ionic separation may not be the only factor giving rise to the behavior of 19, as the photoinduced electron transfer rate constant does not change appreciably, even when the driving force is increased by 0.4 eV through introduction of zinc into the porphyrin macrocycle. In this connection, very rapid photoinduced electron transfer has been observed in other zinc-containing porphyrin-quinone systems [80, 86], and photoinduced electron transfer in zinc-containing porphyrin dyads has... 

The introduction of a carefully located tertiary amine proximal to the boron centre of a fluorescent sensor permits the sensor to function at lower pH and introduces an off on optical response to the system via photoinduced electron transfer (PET). The tertiary amine boronic acid (N-B) interaction in a boronic acid-based PET sensor has strength in the range of 15 25 kJ mol . In an aprotic solvent, the N B dative bond is usually present. However, in a protic media, solvent insertion of the N-B occurs to afford a hydrogen-bonded zwitterionic species. 

Category 111 reactions are one of the most fundamental photochemical processes, thus offering a potentially useful procedure for the introduction of functional group to the substrates. The photochemical generation of the cation radicals of electron-donating substrates (Z)) via the photoinduced electron transfer (PET) can be achieved by the following methods. 

In particular, the introduction of fullerene showed its ability as electron acceptor for performance polymer solar cells. The single-layer device based on conducting polymer was showing the 0.001-0.1 % PCE [22, 23]. Since the discovery of ultrafast photoinduced electron transfer from MDMO-PPV to fullerene, the bilayer cell of conducting polymer/C6o was investigated [24, 25]. The heterojunction device showed the rectification ratios on the order of 10", while energy conversion efficiency was not high. 

A microemulsion, Fig. 1, has a similar organization to that characteristic of a micelle but employs, rather than one, multiple surfactant components, allowing for introduction of other additives into the hydrophobic core [11], As with micelles, microemulsions are optically transparent and can be easily studied by standard spectroscopic methods. One important use of such microemulsions is in the photoinduced initiation of polymerization of monomers with low water solubility many such reactions involve a mechanism occurring through photoinduced interfacial electron transfer. 

The substituents in the anthraquinone ring affected the rate constant of thermal bleaching of derivatives of 1-methylphenoxyanthraquinone (Table 7.1).17,18,26 The substituents that increased the Tt-electron density on the hydrogen atom of the methide group decreased the lifetime of the photoinduced form (Table 7.1).18,26 The introduction of methoxy and piperidine substituents stabilized the photoinduced form (Table 7.1). 

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