Photoredox initiators

Michler s kelene, as photoredox initiator 102 micro-emulsion poly rnerization 64, 250 distinction from emulsion and ininiemulsion... 

Since DMAEMA is an aliphatic tertiaiy amine, the N,N-dimethylaminoethyl moiety of DMAEMA can form a photoredox system with Bp to initiate the photopolymerization of itself The photopolymerization can be carried out at very mild conditions. If the Bp is polymerizable, for example, 4-methacryloyl benzo-phenone, a polymerizable photoredox initiation system will be formed (14), Figure 5 illustrates the thermo- and pH-responsive shape change of asymmetric bilayer sheet made from DMAEMA-BMA copolymer. Since Layer B, in this case, is more hydrophobic than Layer A, the bilayer sheet exhibits an asymmetrical shape change against the pH or temperature change of the environment... 

Metal complex-organic halide redox initiation is the basis of ATRP. Further discussion of systems in this context will be found in Section 9.4, The kinetics and mechanism of redox and photoredox systems involving transition metal complexes in conventional radical polymerization have been reviewed by Bam ford. 

The photovoltaic effect is initiated by light absorption in the electrode material. This is practically important only with semiconductor electrodes, where the photogenerated, excited electrons or holes may, under certain conditions, react with electrolyte redox systems. The photoredox reaction at the illuminated semiconductor thus drives the complementary (dark) reaction at the counterelectrode, which again may (but need not) regenerate the reactant consumed at the photoelectrode. The regenerative mode of operation is, according to the IUPAC recommendation, denoted as photovoltaic cell and the second one as photoelectrolytic cell . Alternative classification and terms will be discussed below. 

The photogalvanic effects are initiated by a homogeneous photoredox reaction of an electrolyte redox system with a suitable photoexcited organic or organometallic substance (dye), S. The photon absorption produces a short-lived, electronically excited dye molecule, S ... 

A regenerative photogalvanic cell with oxidative quenching (Fig. 5.58b) is based, for example, on the Fe3+-Ru(bpy)2+ system. In contrast to the iron-thionine cell, the homogeneous photoredox process takes place near the (optically transparent) cathode. The photoexcited Ru(bpy)2+ ion reduces Fe3+ and the formed Ru(bpy)3+ and Fe2+ are converted at the opposite electrodes to the initial state. 

Photosensitization of diaryliodonium salts by anthracene occurs by a photoredox reaction in which an electron is transferred from an excited singlet or triplet state of the anthracene to the diaryliodonium initiator.13"15,17 The lifetimes of the anthracene singlet and triplet states are on the order of nanoseconds and microseconds respectively, and the bimolecular electron transfer reactions between the anthracene and the initiator are limited by the rate of diffusion of reactants, which in turn depends upon the system viscosity. In this contribution, we have studied the effects of viscosity on the rate of the photosensitization reaction of diaryliodonium salts by anthracene. Using steady-state fluorescence spectroscopy, we have characterized the photosensitization rate in propanol/glycerol solutions of varying viscosities. The results were analyzed using numerical solutions of the photophysical kinetic equations in conjunction with the mathematical relationships provided by the Smoluchowski16 theory for the rate constants of the diffusion-controlled bimolecular reactions. 

Rate of the photochemical reductive dissolution of hematite, = d[Fe(II)]/dt, in the presence of oxalate as a function of the wavelength at constant incident light intensity (I0 = 1000 peinsteins "1 lr1). The hematite suspensions were deaerated initial oxalate concentration = 3.3 mM pH = 3. (In order to keep the rate of the thermal dissolution constant, a high enough concentration or iron(II), [Fe2+] = 0.15 mM, was added to the suspensions from the beginning. Thus, the rates correspond to dissolution rates due to the surface photoredox process). 

The nature of the previously described photoredox mechanisms for other donors leads us to propose that Chaberek s complex (DE) is an exciplex which leads to electron transfer (eq. 24) to produce D and a semioxidized enolate radical E-, which is the actual initiating species (eq. 25). 

Effective dyes were those shown by Watanabe (103) and Calvin (104) to be strongly adsorbed to the pigment surface and to sensitize photoconductivity or photoredox reactions in the semiconductor materials. The initial interaction (eq. 46) is dye sensitized electron-hole pair formation in the semiconductor. 

LMCTegrc0 tj(x is placed at a higher energy than the lowest lying acido ligand to Co (III) excited states and photoredox reactions are, respectively, initiated in each of these excited states, a nonradiative conversion of one into the other electronic state must be sluggish or not available. The experimental observations clearly demonstrate that the photophysics of LMCT states in complexes Com(NH2R)sX2 + with R = alky is different from that with R = H and exemplifies how the properties of the excited state have control over the photochemical properties. 

Stephenson and coworkers applied reductive photoredox catalysis to trigger radical 6-exo cyclizations of co-pyrrole or co-indole-substituted a-bromocarbonyl compounds 124 [186] as well as radical 5-exo cyclizations of 2-bromo-2-(4-pentenyl)malonates 126 (Fig. 32) [187]. These cyclization processes provide bi- or tricyclic products 125 or cyclopentanecarboxylates 127 in moderate to excellent yields. The initial radical was formed with reduced ruthenium catalyst HOB generated similarly as above from 110 and a sacrificial amine... 

Generally, hydride is an electron donor or reductant. Accordingly, (H to Ir ) LMCT excitation could initiate the observed photolysis. However, how can this photoredox reaction be related to water or proton reduction While various hydride complexes undergo such a reductive elimination of H2 their s5mthesis is generally based on complicated procedures and cannot be formed by a simple reaction with water or protons in aqueous solution (8). 

Photoinitiated Addition Polymerisation Chromium (VI) ions undergo a photoredox process to give chromium (V) ions by a charge-transfer mechanism which involves the formation of active HCrO. ions that effectively initiate the photopolymerisation of acrylonitrile while 2,U,6-trimethylbenzoyldiphenylphosphine-... 

TMU2H)3 PMoi2O40 TMUb TMU-derived oxidation products Reduced POM not re-oxidized TMUb Initial report of organic substrate donor-POM acceptor photoredox-active complex 79... 

Figure 5. Relative rate of the light-induced reductive dissolution of hematite in the presence of oxalate as a function of the wavelength. Experimental conditions 0,5 gL 1 hematite initial oxalate concentration 3.3 m mol L 1 pH = 3.0 nitrogen atmosphere. The relative rate is the rate of hematite dissolution at constant incident light intensity. Under the assumption that the light intensity, absorbed by the oscillator that enables the photoredox reaction, corresponds to the incident light intensity, IAX = Iox, the relative rate equals the quantum yield, of dissolved iron(II) formation. As...

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