Photoinduced intermolecular electron

Interdisciplinary research on charge transfer processes has been going on for a long time. The general outline of an intra- or intermolecular photoinduced electron transfer in a donor-acceptor composite can be divided into steps for a clearer understanding [72], Here the letters D and A denote charge donor and acceptor, respectively, and 1 and 3 indicate whether the excited state is a singlet or triplet. 

Intermolecular Photoinduced Electron Transfer Between Monomer Molecules and Donor or Acceptor Molecules... 

In this section an illustrative discussion on kinetics of photopolymerization initiated via an intermolecular photoinduced electron transfer for a dye-tertiary aromatic amine initiating photo-redox couple [193] and for 4-carboxybenzophenone-sulfur-containing carboxylic acids initiating systems will be presented. 

D. Gust, Intermolecular Photoinduced Electron-Reactions ofMetalloporphyrins, in The Porphyrin Handbook, (Eds. R. M. Radish,... 

The second group of intermolecular reactions (2) includes [1, 2, 9, 10, 13, 14] electron transfer, exciplex and excimer formations, and proton transfer processes (Table 1). Photoinduced electron transfer (PET) is often responsible for fluorescence quenching. PET is involved in many photochemical reactions and plays... 

Electron transfer (ET) reactions play a key role in both natural (photosynthesis, metabolism) and industrial processes (photography, polymerisation, solar cells). The study of intermolecular photoinduced ET reactions in solution is complicated by diffusion. In fact, as soon as the latter is slower than the ET process, it is not anymore possible to measure km, the intrinsic ET rate constant, directly [1], One way to circumvent this problem, it is to work in a reacting solvent [2]. However, in this case, the relationship between the observed quenching rate constant and k T is not clear. Indeed, it has been suggested that several solvent molecules could act as efficient donors [3]. In this situation, the measured rate constant is the sum of the individual ksr-... 

Photoinduced electron-transfer reactions generate the radical ion species from the electron-donating molecule to the electron-accepting molecules. The radical cations of aromatic compounds are favorably attacked by nucleophiles [Eq. (5)]. On the contrary, the radical anions of aromatic compounds react with electrophiles [Eq. (6)] or carbon radical species generated from the radical cations [Eq. (7)]. In some cases, the coupling reactions between the radical cations and the radical anions directly take place [Eq. (8)] or the proton transfer from the radical cation to the radical anion followed by the radical coupling occurs as a major pathway. In this section, we will mainly deal with the intermolecular and intramolecular photoaddition to the aromatic rings via photoinduced electron transfer. 

Photoinduced electron transfer from the amine to C6o to yield a radical ion pair is suggested to be the initial step for the formation of 54a-b. This is followed by deprotonation of the amine cation by the fullerene anion to give an a-aminoalkyl and HC6o radical pain [134], Subsequent combination of the radical pair leads to the final product. Formation of 55 is likely to be initiated by PET from 54b to C6o. This is then followed by successive intermolecular proton transfer, hydrogen abstraction, and ring closure to give l,2-H2C6o and 55 (Scheme 21). 

Photoinduced electron transfer occurs through excitation of the 400-nm absorption bands of the donor chromophores based on the aminonapthalene-dicarboximide derivatives. The tails of the dopants absorption bands extend to at least 500 nm, which allows for the use of an Ar+ laser. Figure 8 illustrates the ground-state absorption spectra of the donor and acceptor for both the intramolecular and intermolecular charge transfer dopants in toluene. The spectra are similar for all of the dopants, with the exception of 2, which has a 50-nm red-shifted absorption band. The inset illustrates the broadened spectra in the liquid crystalline environment. The extinction coefficient at 457 nm varies from approximately 1000 M-1 cm-1 for 4, 2000 M-1 cm-1 for 1, 5000 M-1 cm-1 for 3, and 10,000 M-1 cm-1 for 2. 

Switching systems based on photochromic behavior,I29 43,45 77-100 optical control of chirality,175 76 1011 fluorescence,[102-108] intersystem crossing,[109-113] electro-chemically and photochemical induced changes in liquid crystals,l114-119 thin films,170,120-1291 and membranes,[130,131] and photoinduced electron and energy transfer1132-1501 have been synthesized and studied. The fastest of these processes are intramolecular and intermolecular electron and energy transfer. This chapter details research in the development and applications of molecular switches based on these processes. 

Photoexcitation of a deaerated PhCN solution of Acr+-Mes by a nanosecond laser light flash at 430 nm results in the formation of Acr -Mes+ with a quantum yield close to unity (98 %) via photoinduced electron transfer from the mesitylene moiety to the singlet excited state of the acridinium ion moiety ( Acr -Mes) [54]. The decay of Acr -Mes+ obeyed second- rather than first-order kinetics at ambient temperature as observed in the case of Fc+-ZnP-H2P-C60 , when the bimo-lecular back electron transfer predominates owing to the slow intramolecular back electron transfer (see above) [50]. In contrast, the decay of Acr -Mes+ obeys first-order kinetics in PhCN at high temperatures (e.g. 373 K). This indicates that the rate of the intramolecular back electron transfer of Acr -Mes4 becomes much faster than the rate of the intermolecular back electron transfer at higher tempera-... 

The photoinduced electron transfer (PET) is especially important in the case of large or giant molecules (supermolecules), ie systems made up of molecular components in the same way as molecules are made up of atoms [11-19], As the systems are made up of a number of discrete components held together by different but not always exactly specified forces (covalent bonds, electrostatic interactions, hydrogen bonds, or other intermolecular interactions), the photoinduced electron transfer or energy transfer in these systems may be formally treated as intermolecular [20],... 

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