Redox photo induced

Reaction Mechanism of Vinyl Polymerization with Amine in Redox and Photo-Induced Charge-Transfer Initiation Systems... 

A substantial number of photo-induced charge transfer polymerizations have been known to proceed through N-vinylcarbazole (VCZ) as an electron-donor monomer, but much less attention was paid to the polymerization of acrylic monomer as an electron receptor in the presence of amine as donor. The photo-induced charge-transfer polymerization of electron-attracting monomers, such as methyl acrylate(MA) and acrylonitrile (AN), have been recently studied [4]. In this paper, some results of our research on the reaction mechanism of vinyl polymerization with amine in redox and photo-induced charge transfer initiation systems are reviewed. 

Graft Copolymerization of Vinyl Monomers Onto Macromolecules Having Active Pendant Group via Ceric Ion Redox or Photo-Induced Charge-Transfer Initiation... 

Therefore, the graft copolymerization of vinyl monomers onto macromolecules having active an pendant group can be achieved either by redox initiation with a Ce(IV) ion or by photo-induced charge-transfer initiation with BP, depending on the structure of the active groups. 

CPOs are best characterized by the following three features 1) axial coordination to the incorporated metals, 2) specific nano-sized space created by rigid porphyrin panels, and 3) specific (photo-induced) redox reactions associated with the porphyrin s rr-electron system. In this chapter, some examples are reviewed based on these properties. 

A combination of cat. Ybt and A1 is effective for the photo-induced catalytic hydrogenative debromination of alkyl bromide (Scheme 28) [69]. The ytterbium catalyst forms a reversible redox cycle in the presence of Al. In both vanadium- and ytterbium-catalyzed reactions, the multi-component redox systems are achieved by an appropriate combination of a catalyst and a co-reductant as described in the pinacol coupling, which is mostly dependent on their redox potentials. 

Similar photo-induced reductive dissolution to that reported for lepidocrocite in the presence of citric acid has been observed for hematite (a-Fe203) in the presence of S(IV) oxyanions (42) (see Figure 3). As shown in the conceptual model of Faust and Hoffmann (42) in Figure 4, two major pathways may lead to the production of Fe(II)ag i) surface redox reactions, both photochemical and thermal (dark), involving Fe(III)-S(IV) surface complexes (reactions 3 and 4 in Figure 4), and ii) aqueous phase photochemical and thermal redox reactions (reactions 11 and 12 in Figure 4). However, the rate of hematite dissolution (reaction 5) limits the rate at which Fe(II)aq may be produced by aqueous phase pathways (reactions 11 and 12) by limiting the availability of Fe(III)aq for such reactions. The rate of total aqueous iron production (d[Fe(aq)]T/dt = d [Fe(III)aq] +... 

From our observations, we feel it is unlikely that photo-induced redox reactions are occurring in the present studies. However, at wavelength < 300 nm photodissociation of oxyhemoglobin results in the formation of the 02" radical anion (34). 

To design photo-induced electron transfer devices, the group of Nishino [69] reported the preparation of a bis-a-helical nanostructure, 74. The peptidic framework was designed to orient rigidly in space the redox triad, composed of a Ru2 + complex, an anthraquinone, and two propylviologens, when incorporated in a lipid bilayer (Fig. 28). Although the compound exhibited a strong a-helical content in methanol, its conformation in a vesicle bilayer was different and undetermi ned. Nevertheless, irradiation of the Ru(II) complex of 74 resulted in a slow electron transfer. 

Fig. 30. Schematic representation of a photo-electroswitch where the emission properties of a photosensitive centre are modulated by the electrochemical interconversion of a redox centre inducing luminescence quenching by energy or electron transfer.

The effect of temperature on photo-induced biosynthesis of carotenoids in Neuro-spora crassa has been studied368 and the ability of redox dyes to act as artificial photoreceptors in a similar system has been investigated.369... 

Perylene and tetracene both undergo photo-induced electron-transfer reactions with pyromellitic anhydride (Levin, 1976). If a mixture of perylene and tetracene is used, and the light absorbed by the perylene, the perylene radical cation will be formed which because of the relative oxidation potentials will react with tetracene to give the tetracene radical ion. Thus the photogenerated perylene radical cation has undergone a redox reaction with tetracene. In effect, the perylene has acted as a sensitiser for the production of the tetracene radical cation. This type of sensitisation has been used to effect a number of reactions. 

The excited-state redox reaction, equation (8.12), is thermodynamically favorable (E° > 0) while ground-state reaction, equation (8.13) is not (E° < 0). Therefore, a mixture of [Cr(phen)3]3+ and such a substrate will only undergo a redox reaction after the chromium complex has been excited. This is the process of photo-induced electron transfer light initiates an electron-transfer reaction. This experiment will explore how substrates such as DNA may be oxidized by the excited-state [Cr(phen)3]3+ complex. Because the electron-transfer reaction competes kinetically with luminescence, the presence of such a suitable substrate leads to a decrease in the intensity of luminescence. For this reason, the substrate is termed a quencher. 

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