Photoinduced transformations

Photoinduced transformations of photochromes (spiropyrans, furan-derived fulgides, dithienylethenes) in polymers 98PAC2157. 

All the applications of photocatalysis have one common point they can help in obtaining processes that obey the requirements of green chemistry. In fact, many of the principles of sustainable chemistry are applied to photoinduced transformations in all areas of application [18]. The major achievement of photocatalysis is the use of catalysis and light, which are two of the pillars of sustainable chemistry. 

At the present time, most of the positive photoresists used in the manufacture of microcircuits consist of a low molecular weight phenolic resin and a photoactive dissolution inhibitor. This composite system is not readily soluble in aqueous base but becomes so upon irradiation with ultraviolet light. When this resist is exposed, the dissolution inhibitor, a diazoketone, undergoes a Wolff rearrangement followed by reaction with ambient water to produce a substituted indene carboxylic acid. This photoinduced transformation of the photoactive compound from a hydrophobic molecule to a hydrophillic carboxylic acid allows the resin to be rapidly dissolved by the developer. (L2,3)... 

In the case of l-methyl-4-oxy-9,10-anthraquinone (II, R1 = CH3, R2 = H, R3 = OH), the photoinduced transfer of a hydrogen atom from a methyl group to oxygen occurs together with the thermal transfer of a proton from the OH group to the second oxygen (Scheme 12). The related photoinduced transformations were observed for the derivatives of 1-alkyl and 1-benzylanthraquinones.8,9,23,26... 

Our objective in this article will be to select critical examples dealing with the photooxygenation of organic substrates, in which experimental evidence strongly support a photochemically initiated electron-transfer mechanism, thus opening an entirely new perspective in peroxide chemistry. Our aim will be also to introduce the interested reader to mechanistic features which must be dealt with in investigating photoinduced transformations. On the other hand, because this area is inherently interdisciplinary, it is rather hard to provide a detailed compilation of all work relevant to the photoinduced reactions of concern. Thus, except for few cases, no attempt will be made to discuss the diversified chemistry of photosensitized electron-transfer processes, extensively reported in several excellent reviews [69-72]. 

Photochromism A photoinduced transformation of a molecular structure (e.g. of a solution), photochemically and/or thermally reversible, that produces a spectral change, typically, but not necessarily, of visible color. 

The photoinduced transformation of 3-hydroxyisoxazole (254) into 2(3 )-oxazoIone was successfully applied to the synthesis of muscazone (256), probably via an intermediate a-lactam (255) (Scheme 48). ... 

Fig. 19.2. Photoinduced transformations in pristine and functionalized gold nanoparticles.

Turnover number (TON) refers to the ratio of the number of photoinduced transformations for a given period of time to the number of photocatalytic sites (or centres) in heterogeneous photocatalysis, or to the number of photocatalyst molecules in homogeneous photocatalysis. TON is a dimensionless quantity (see Section 5.2.6 and also Serpone and Emeline, 2002). 

Oxaziridines are of interest in their own right and as intermediates in various photorearrangements. It has been shown that the nature of the nitrogen substituent does not affect the regioselectivity of lactam formation on irradiation of spiro-oxaziridines. The oxaziridine (80) has been proposed without any real evidence as an intermediate in the photoinduced transformation of tra 5-canadine iV-oxide... 

Alkoxyalkylhydroquinones, e. g., CLXII, formed in the photoinduced transformation of tert-butylated benzoquinones, exhibit strong antioxidation effects in polypropylene214. As long as compounds of this type are present in an oxidized polymer only in very low concentrations, they only retard the oxidation. This is probably the cause of the observed retardation effect of 2,6-di-tert-butyl-1,4-benzoquinone in the oxidation of hihg-impact polystyrene95. ... 

Compounds that evaporate may remain in the gas phase but can also distribute onto particles in the atmosphere. Other compounds may be released on particles such as the polynuclear aromatic hydrocarbons produced in the combustion of diesel fuel or in wood smoke. It is of interest to explore how compounds distribute between the particle and the vapor phase since this will influence their environmental behavior. Distribution onto a particle will enhance the potential for wet or dry deposition, major transport processes for moving compounds to surface water or onto vegetation. Compounds in the vapor phase will be subject to a range of photoinduced transformation processes, but how susceptible are compounds sorbed on particles ... 

Nakanishi, K. and Crouch, R. (1995) Application of artificial pigments to structure determination and study of photoinduced transformants of retinal proteins. Israel J. Chem. 35, 253-272. 

Donadio, D. and Bemasconi, M., Ab initio simulation of photoinduced transformation of small rings in amorphous sihca, Phys. Rev. B 71, 073307 (2005). 

Hg. 28 Photoinduced transformations of matrix-isolated thiophenol. Abbreviations PhSH, thiophenol 1 cyclohexa-2,4-diene-l-thione 2, cyclohexa-2,5-diene-l-thione ThiyI - phenylthiyl radical. Direct PhSH 2 photoisomerization could not be confirmed or discarded." Reproduced from Ref. 79 with permission from the PCCP Owner Societies. 

Fig. 29 Photoinduced transformation taken place on o-nitroaniline isolated in an argon matrix upon UV irradiation at 185nm. ° Reprinted from C. Zhang and M. Chen, Photoinduced intramolecular hydrogen transfer in ortho-nitroaniline A matrix-isolation infrared spectroscopic and quantum-chemical study, J, Mol. Struct, 2013, 1037, 144-147, with permission from Elsevier,...

Y. V. Razskazovskii, Kinetics and Mechanisms of Photoinduced Transformations in Solid Solutions of Thiols, Ph.D. Thesis, Moscow State University (1984). 

Lahiri D, Subramanian V, Shibata T, Wolf EE, Bunker BA, Kamat PV (2003) Photoinduced transformations at semiconduc-tor/metal interfaces X-ray absorption studies of titania/gold films. J Appl Phys 93(5) 2575-2582... 

Tanaka K. and Ohtsuka Y., Measurements of photoinduced transformations in amorphous AS2S3 films by optical waveguiding, J. Appl. Phys., 49, 6132-6135 (1979). 

Scheme 2.4 Reversible photoinduced transformations of (a) azobenzene and (b) spiropyran derivatives.

Suginome, H., Mizuguchi, X, Honda, S., and Masamune, X, Photoinduced transformations. 33. Mechanism of photoinduced rearrangement of a (22S, 25S)-N-acetylveratr-13(17)-enin-ll-yl nitrite, a fused cyclopentyl nitrite, to a nitrone, /. Chem. Soc., Perkin Trans. 1, 927, 1977. 

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