The Chemistry of Excited Complexes: a Survey of Reactions

Davidson, R. S.

doi:10.1016/s0065-3160(08)60222-1

Cited by 80 publications

(27 citation statements)

References 563 publications

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“…4,5 Type II photoinitiators are based on compounds, mostly aromatic ketones, whose triplet excited states react with hydrogen donors under H-abstraction or electron donors to produce initiating radicals. 6,7 Because the type II initiation is based on bimolecular reaction, they are generally slower than type I photoinitiators, which are based on unimolecular formation of radicals.…”

Section: Introductionmentioning

confidence: 99%

Mechanistic Studies of Photoinitiated Free Radical Polymerization Using a Bifunctional Thioxanthone Acetic Acid Derivative as Photoinitiator

et al. 2009

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A bifunctional photoinitiator for free radical polymerization, thioxanthone catechol-O,O 0 -diacetic acid, was synthesized, characterized, and compared to photoinitiator parameters of the monofunctional analogue, 2-(carboxymethoxy)thioxanthone. Photophysical studies such as fluorescence, phosphorescence, and laser flash photolysis in addition to photopolymerizations of methyl methacrylate show that the bifunctional photoinitiator is more efficient in polymer generation than the monofunctional derivative. These studies suggest that initiator radicals are generated from a π-π* triplet state in an intramolecular electron transfer, followed by proton transfer and decarboxylation to generate alkyl radicals, which initiate polymerization. The initial electron transfer is faster for the bifunctional photoinitiator than the monofunctional derivative, which is based on laser flash photolysis studies. Because of the relatively fast intramolecular radical generation from the triplet state (triplet lifetime = 490 ns), quenching by molecular oxygen is insignificant and polymerization of methyl methacrylate proceeds efficiently without deoxygenation. At higher concentrations of initiator (∼5 mM) intermolecular electron transfer competes with intramolecular electron transfer. Both processes, inter-and intramolecular processes, yield initiating alkyl radicals.

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Section: Introductionmentioning

confidence: 99%

Mechanistic Studies of Photoinitiated Free Radical Polymerization Using a Bifunctional Thioxanthone Acetic Acid Derivative as Photoinitiator

et al. 2009

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“…Photoinitiated radical polymerization may be initiated by bond cleavage (type I) and H-abstraction type (type II) initiators. 1 Type II photoinitiators are a second class of photoinitiators based on compounds whose triplet excited states readily react with hydrogen donors, thereby producing initiating radicals [6][7][8] (Scheme 1). Because of the bimolecular radical generation process, they are generally slower than type I photoinitiators, which form radicals unimolecularly.…”

Section: Introductionmentioning

confidence: 99%

Thioxanthone−Anthracene: A New Photoinitiator for Free Radical Polymerization in the Presence of Oxygen

et al. 2007

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A novel thioxanthone-anthracene (TX-A) photoinitiator, namely 5-thia-pentacene-14-one, possessing the respective photochromic groups was synthesized. TX-A is an efficient photoinitiator for free radical polymerization of acrylic and styrenic type monomers in the presence of oxygen. UV-vis, FT-IR, and fluorescence spectroscopic and polymerization studies revealed that photoinitiation occurs through anthracene chromophore. In contrast to thioxanthone-based photoinitiators, TX-A does not require an additional hydrogen donor for the initiation.

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“…Most of this research has focused on Type I photoinitiators, which upon irradiation undergoes an R-cleavage process to form two radical species. Type II photoinitiators are a second class of photoinitiators and are based on compounds whose triplet excited states are reacted with hydrogen donors thereby producing an initiating radical [6][7][8] (Scheme 1). Because the initiation is based on bimolecular reaction, they are generally slower than Type I photoinitiators which are based on unimolecular formation of radicals.…”

Section: Introductionmentioning

confidence: 99%

Mechanistic Study of Photoinitiated Free Radical Polymerization Using Thioxanthone Thioacetic Acid as One-Component Type II Photoinitiator

et al. 2005

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A mechanistic study concerning photoinitiated free radical polymerization using thioxanthone thio-acetic acid (TX-S-CH 2-COOH) as one-component Type II photoinitiator was performed. Steady-state and time-resolved fluorescence and phosphorescence spectroscopy, as well as laser flash photolysis was employed to study the photophysics and photochemistry of TX-S-CH 2-COOH. The initiator undergoes efficient intersystem crossing into the triplet state and the lowest triplet state posseses π-π* configuration. In contrast to the unsubstituted thioxanthone, TX-S-CH 2-COOH shows an unusually short triplet lifetime (65 ns) indicating an intramolecular reaction. From fluoroscence, phosphorescence, and laser flash photolysis studies, in conjunction with photopolymerization experiments, we propose that TX-S-CH 2-COOH triplets undergo intramolecular electron transfer followed by hydrogen abstraction and decarboxylation producing alkyl radicals, which are the active initiator radicals in photoinduced polymerization. At low initiator concentrations (below 5 × 10 -3 M) this intramolecular reaction is the dominant path. At concentrations above 5 × 10 -3 M, however, the respective intermolecular reactions may be operative.

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The Chemistry of Excited Complexes: a Survey of Reactions

Cited by 80 publications

References 563 publications

Mechanistic Studies of Photoinitiated Free Radical Polymerization Using a Bifunctional Thioxanthone Acetic Acid Derivative as Photoinitiator

Mechanistic Studies of Photoinitiated Free Radical Polymerization Using a Bifunctional Thioxanthone Acetic Acid Derivative as Photoinitiator

Thioxanthone−Anthracene: A New Photoinitiator for Free Radical Polymerization in the Presence of Oxygen

Mechanistic Study of Photoinitiated Free Radical Polymerization Using Thioxanthone Thioacetic Acid as One-Component Type II Photoinitiator

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