Photo initiators visible light

This system is claimed to possess good thermal stability and high photochemical driving force. Upon irradiation, an electron transfer reaction between excited dye and iodonium salt leads to photo bleaching of the squarylium dye and generation of active radicals. The results obtained indicate that squarylium dye and iodonium salt systems will effectively initiate visible light photopolymerization and photocrosslinking of acrylic esters. ... 

With unimplanted or chemically doped titanium oxide photocatalysts, the photo catalytic reaction does not proceed under visible light irradiation (A > 450 nm). However, we have found that visible light irradiation of metal ion-implanted titanium oxide photocatalysts can initiate various significant photocatalytic... 

X> 350 nm) and to return to tKe initial value in 30 h in the dark at 20 °C (Fig. 4). The decrease is not due to the intramolecular dipole-dipole interaction, because the polarity of the solvent u was very high and the photo-effect was not observed for polymers with long flexible methylene chains. The slow recovery of the viscosity in the dark was accelerated by visible light irradiation (A, > 470 nm). When alternately irradiated with ultraviolet and visible li t, the viscosity reversibly changed as much as )% (Fig. 5). 

In practice such salts do function as photo-initiators but via a mechanism which involves formation of protonic acid, not Lewis acid, as shown in Scheme 10. Furthermore, though the salts themselves require irradiation with u.v. light, photolysis is readily sensitized by dyes and allows the use of visible wavelengths. ... 

Photocontrol of enzyme activity has also been demonstrated with membrane-bound enzymes. Urease was modified with a splropyran and Immobilized In a collagen membrane matrix. The activity of the modified urease decreased with ultraviolet Irradiation and then was restored to the Initial activity with visible light Irradiation (38). A collagen membrane matrix has also been modified with a splropyran compound to be photosensitive. Trypsin was Immobilized in the photosensitive collagen membrane matrix. The activity of the trypsin membrane under visible light decreased by about 20% in the dark (39). The splropyran-modifled membrane was hydrophilic In the dark and turned hydrophobic under visible light, which may have been responsible for the photo change in the apparent diffusion coefficient of the substrate within the membrane matrix. 

Various other metal salts were also reported as being capable of photo initiating free-radical polymerizations. Thus, salts of boron compounds are often used in aehieving cures of coatings and ink formulations that are based on acrylates and methacrylates. The aryl alkyl borates that are paired with cationic chromophores can act as co-initiators in either UV or in visible light... 

Dyes comprise a large fraction of visible light photoinitiators because their excited electronic states are more easily attained. Co-initiators, such as tertiary amines, iodonium salts, triazines, or hexaarylbisimidazoles, are required since dye photochemistry entails either a photoreduction or photo-oxidation mechanism. Numerous dye families are available for selection of an appropriate visible initiation wavelength an example of a thiazine dye (with an absorption peak aroimd 675 nm) is methylene blue (11). 

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