Some Applications of Organic Photochemistry

The following additional examples offer a hint of the utility of organic photochemistry in s)mthesis. A [2 + 2] photochemical cycloaddition was a key step in the synthesis of cubane. S)mthesis of 2-bromocyclopenta-2,4-dienone resulted in a spontaneous Diels-Alder reaction, which produced 132. The monoketal of the dimer (133) underwent intramolecular photocycloaddition to produce 134 (equation 12.85). The Favorskii reaction of 134 gave 135, which was decarboxylated to 136 (equation 12.86). Hydrolysis of the ketal gave 137. Subsequent Favorskii reaction to 138 and then decarboxylation produced cubane, 139. Similarly, de Meijere and co-workers reported that the intramolecular [2 + 2] photochemical cycloaddition of 140 produced octacyclopropylcubane (141, equation 12.87) Meder and coworkers utilized the reaction sequence in equation 12.88 to convert the diazo compound 142 into tetra-f-butylcyclobutadiene (143) and tetra-f-butyltetra-hedrane (144).  

The use of chiral sensitizers or of circularly polarized light can lead to asymmetric photochemical synthesis. For a review, see Inoue, Y. Chem. Rev. 1992, 92, 741. See also equation 12.99. 

Protti, S. Dondi, D. Fagnoni, M. Albini, A. PureAppl. Chem. 2007, 79,1929 Oelgemoller, M. Jung, C. Mattay, J. Pure Appl. Chem. 2007, 79,1939. 

For discussions of synthetic organic photochemistry, see Horspool, W. M., Ed. Synthetic Organic Photochemistry Plenum Press New York, 1984 Srinivasan, R. Roberts, T. D., Eds. Organic Photochemical Syntheses, Vol. 1 Wiley-Interscience New York, 1971 Srinivasan, R., Ed. Organic Photochemical Syntheses, Vol. 2 Wiley-Interscience New York, 1976 reference 169 Ninomiya, I. Naito, T. Photochemical Synthesis Academic Press London, 1989 Griesbeck, A. G. Mattay, J., Eds. Synthetic Organic Photochemistry CRC Press Boca Raton, FL, 2004. 

PureAppl. Chem. 1991,63,275. See also Maier, G. Wolf, R. Kalinowski, H.-O. Angew. Chem. Int. Ed. Engl. 1992, 31, 738. 

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Chapter 1 Some Theoretical Applications of Organic Photochemistry Excited State and Open Shell Examples. 1... 

The photochemistry of small molecule LC materials has been an active area of research for many years and has been reviewed recently [9]. The photochemistry of LC polymers, per se, has received much less attention although two brief reviews have appeared [5,10], and there has been a considerable effort to apply some simple photochemical transformations such as trans-cis photoisomerization, to the development of practical devices [1-6]. This section is divided into three parts. In Part A, chromophore aggregation, which seems to be important in almost all the cases in which careful UV-Vis and/or fluorescence studies of films of pure LC polymers have been made, is explicitly discussed. Part B is devoted to a thorough review, organized by chromophore type, of the photochemistry and related photophysics of LC polymers. No attempt has been made to extensively cross-reference the work on LC polymers to the hundreds of papers and reviews on analogous non-LC compounds. However, when it seemed particularly appropriate or interesting, experiments related to optical applications of the photochemistry of LC polymers are briefly described. In Part C, a few experiments are described in which a classical photophysical method, fluorescence spectroscopy, is used to probe the microstructures of some LC polymers. 

This chapter provides a brief description of the matrix-isolation technique and then gives some examples of its applications in the study of organic photochemistry. The topics that have been included have been selected from areas of photochemical research to which matrix isolation has made an important and sustained contribution. The choices have been made from among many possibiHties and inevitably reflect the author s personal interests, but, in addition to this more general chapter, two specific areas of matrix photochemistry, alkenes and small ring compounds, are covered in Chapters Y and Z, respectively. 

The theoretical treatment of photo-excitation processes is a field for the specialist, and is beyond the scope of this book. The complexity both of the physical concepts, and of the structures of some photochemical transformation products, has tended in the past to frighten many organic chemists into regarding photochemistry as a field outside the range of ordinary mechanistic interpretation, but the last few years have seen the successful application of normal mechanistic principles to excited molecules [i]. 

Although TP photochemistry has been successfully applied for some applications, it is still in its infancy. The results summarized in this chapter are systematically grouped to assist in further development and use of TP absorbing materials and related applications in material science and engineering. The interdisciplinary relations described are useful for future work in physical, organic, and polymer chemistry as well as experimental physics. Some selected reviews are complementary to this chapter [16, 23, 31, 35, 41,45, 50, 53, 70, 71, 86, 127, 129, 272-277],... 

Although organic photochemistry has experienced remarkable growth, applications of photochemical synthetic methods in the chemical industry have been mostly limited to radical reactions, such as photohalogenation (this section), photopolymerization (Section 6.8.1) and to some extent photosulfochlorination, photooxidation (Section 6.7) and photonitrosylation, although some other reactions are also being used.155... 

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