Photoinduced electron transfer mechanism

The advantage of employing periodic perturbation of light intensity, e.g., using a chopper, and phase-sensitive detection are beyond a simple enhancement of the signal-to-noise ratio. For photoinduced electron-transfer mechanisms, as schematized in Fig. 11, the... 

Most PET fluorescent sensors for cations are based on the principle displayed in Figure 10.7, but other photoinduced electron transfer mechanisms can take place with transition metal ions (Fabbrizzi et al., 1996 Bergonzi et al., 1998). In fact, 3d metals exhibit redox activity and electron transfer can occur from the fluorophore... 

Figure 15-29. The proposed photoinduced electron-transfer mechanism in DACN-DPA and DMABN molecules involves the tttt tut state switch followed by the charge shift that leads to full charge separation. (Reprinted with permission from Refs. [44, 59].)...

A photoinduced electron transfer mechanism has been proposed by de Mayo and coworkers to explain the products arising from the irradiation of 1,1-di-p-anisylethene in benzene-trifluoroacetic acid solutions [73]. Photolysis (>430 nm) of the (di-p-anisylmethyl)methyl cation 30 resulted in electron transfer from the neutral substrate 29 as shown in the Scheme 10. No reaction occurred under these conditions in the absence of acid. The quantum yields of the photoproducts are... 

The kei value increases with an increase in the driving force (-AG°et) and they agree with the kq and obs values (Table 3). Such agreement confirms the validity of the photoinduced electron transfer mechanisms shown in Schemes 6 and 7. 

The photosensitized monomerization of thymine dimers has been achieved in the presence of reduced flavin,and pyrimidine dimers undergo cleavage by light-utilizing enzymes which are thought to act by a photoinduced electron transfer mechanism. ... 

State pyrene by Cu(II) ion during the sol-to-gel conversion has contributed to understanding of photoinduced electron-transfer mechanisms in sol-gel monoliths (236, 237). The smdy of the charge separation between pyrene and an electron acceptor molecule is more applicable to the discussion of photonics and will be discussed in Section V.B. 

Detailed studies on the photoinduced electron transfer mechanism between PZn and PAu in I" " point to the involvement of the orbitals of the bridging phenantroline, in a superexchange mechanism, whereas the charge recombination step (5) is likely to occur through the space separating the two units, very likely with the intermediation of solvent molecules [53]. 

On the basis of the overall results, an energy diagram for CT-allowing AN-s-BPDA-AN can be depicted as shown in Fig. 19. In the proposed mechanism, the intermolecular CT fluorescence emission occurs via two different pathways first, the photoinduced electron transfer from a local excited state at the biphenyldiimide unit to the spatially adjacent ground-state PDA residue, and second, the direct excitation at the CT absorption band. The first process is possible even at very low CTC concentration as in the PI film cured at a low temperature such as 200°C. Such a photoinduced electron transfer mechanism will be theoretically discussed again later. In fully aromatic s-BPDA-PDA, both the fluorescence from Si (tt, tt ) and phosphorescence from Ti (tt, tt ) are not observed practically. The results are probably attributed to the considerably fast CT process from Si (it, tt ). 

Similar base-promoted photoreaction of unactivated arenes (137) and (138) or heteroarenes by use of visible light occurred to give biaryls (139) in the presence of Ir(ppy)3 (ppy phenylpyridine) as photoredox sensitizer/ A photoinduced electron transfer mechanism was proposed. 

Why is the photoinduced electron transfer so strongly inhibited in the polydiacetylenes The energetics of the donor and acceptor components and the relative positions of the various energy levels are important parameters of the photoinduced electron transfer mechanism. The ionization potentials of the polydiacetylenes are around 5.5 eV [170], nearly identical to the ionization potentials of polythiophenes (5.2 eV [171]) and very close to those of the PPVs (5.11 eV [171]). The optical absorption gaps are comparable. Thus, the extraordinary difference— ultrafast photoinduced electron transfer in the PPVs and P3ATs and the complete inhibition of photoinduced electron transfer in the PDAs— must have its origin in the photophysics of the polydiacetylene. 

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