Solid-state, photochemistry

The low solubility of fullerene (Ceo) in common organic solvents such as THE, MeCN and DCM interferes with its functionalization, which is a key step for its synthetic applications. Solid state photochemistry is a powerful strategy for overcoming this difficulty. Thus a 1 1 mixture of Cgo and 9-methylanthra-cene (Equation 4.10, R = Me) exposed to a high-pressure mercury lamp gives the adduct 72 (R = Me) with 68% conversion [51]. No 9-methylanthracene dimers were detected. Anthracene does not react with Ceo under these conditions this has been correlated to its ionization potential which is lower than that of the 9-methyl derivative. This suggests that the Diels-Alder reaction proceeds via photo-induced electron transfer from 9-methylanthracene to the triplet excited state of Ceo-... 

The solid state photochemistry of the salts of carboxylic acids with optically active primary amines has been studied111. Enantiomeric excesses ranging from 14-80% can be achieved (equation 59). 

Solid-state photochemistry of (—)-2-chloro-2-nitrosocamphane 275 was studied145 by irradiation of the blue-crystal with red light to invert the configuration at C(2) (equation 123). This also causes a photochemically initiated Beckmann rearrangement to form chloroxime 276 to give nitroxide radical 278 (equation 124). The intermediate chloro oxime 276 is proposed to arise from the njr excitation and is believed to be the common intermediate for the photo-epimerization and Beckmann rearrangement. Extended... 

Table 2 Asymmetric induction in the solid-state photochemistry of compounds 29a-d ...

The X-ray analyses reveal that, as in the case of salt 37b, enantio- and dia-stereoselectivity in the solid-state photochemistry of salt 39 are conformationally... 

The examples of ex situ steady-state X-ray photodiffraction utihzed to follow the photodimerizations of olefin bonds in a single-crystal-to-single-crystal (or nearly so) manner are ubiquitous in the chemical literature. The interest of sohd-state chemists in this reaction dates back to the work of Cohen and Schmidt [30, 31], and it has become much of a guinea pig in organic solid-state photochemistry. In 1993, Enkelmann and collaborators published two seminal papers in the Journal of the American Chemical Society [32] and in Angewandte Chemie [33], where they presented a series of structures of a-tra s-cinnamic acid crystals reacted to various extents. These reports laid the way for a plethora of later studies on the olefin photodimerization reaction. The convenience of the high conversion and the simple mechanism, combined with the relatively small structural perturbation that it requires, has turned this reaction into a very useful tool to probe intermolecular... 

It may be argued whethere these examples, which have usually employed X-ray diffraction analysis of previously UV irradiated crystals, fall within the domain of the X-ray photodiffraction methods or solid state photochemistry, and whether the term X-ray photodiffraction should be reserved only for time-dependent studies. Although that in the original publications many of these examples have not been labeled as such, because they involve application of XRD methods to study photochemical reactions, we believe that they should he considered as part of the X-ray photodiffraction method in its broadest definition. 

For a collection of selected papers by Schmidt see G. M. J. Schmidt et al., Solid State Photochemistry, D. Guinsburg, Ed., Verlag Chemie, Weinheim, 1976. 

What is lacking at this point in theories relating lattice restraints and chemical reactivity is the identification of specific steric interactions which alter reactivity and an estimation of their magnitude. This requires an extensive database of structure-reactivity information for a series of closely related compounds. This we have from our studies on the solid state photochemistry and X-ray crystallography of a large number of variously substituted bicyclic dienones of general structure L (5). In this series, we recently observed a photorearrangement... 

Schmidt, G.M.J. "Solid State Photochemistry Ginsburg, D., Ed. Verlag Chemie, New York, 1976. 

A new method for assymmetric induction in the solid state photochemistry of prochiral amine salt with an optically active acid has been developed. For example, (+)-55 and (—)-55 were obtained by irradiation of the salts 54a and 54b, respectively, at -40°C in the solid state [29]. 

The central problem in organic solid-state photochemistry is the preorganization of molecules satisfying the topochemical postulates. Schmidt coined the term crystal engineering for this problem of supramolecular assembly. Indeed, the importance of crystal engineering is fundamental to areas as diverse as nonlinear optics, high- /) superconductors, and the generation of polymorph forms in pharmaceuticals. 

Ruzicka opined that a crystal is a chemical cemetery (quoted from Ref. [65]). What he meant was that molecules in a crystal are lifeless. However, the reality is that at any given temperature, the atoms and molecules in a crystal are not at rest. In the context of solid-state photochemistry, this immediately suggests that the percentage yield and the rate of reaction would depend on the temperature of irradiation. 

This solid-state reaction was discovered by Aoyama etal. and subsequently studied in more detail by Toda etal. Aoyama, H., Hasegawa, T., and Omote, Y. (1979) Solid state photochemistry of jV,jV-dialkyl-ct-oxoamides. Type II reactions in the crystalline state, J. Am. Chem. Soc., 101, 5343-5347. 

Crystal-to-Crystal Solid-State Photochemistry Absolute Asymmetric (3-Thiolactam Synthesis from an Achiral a,(3-Unsatur ated Thioamide, J. Am. Chem. Soc. 118, 10664-10665. (b) Sakamoto, M., Takahashi, M., Arai, W., Mino, T., Yamaguchi, K., Watanabe, S., and Fujita, T. (2000) Solid-State Photochemistry Absolute Asymmetric (3-Thiolactam Synthesis from Achiral N,N-Dibenzyl-a,6-unsaturated Thioamides, Tetrahedron, 56, 6795-6804. (c) Hosoya, T., Ohhara, T., Uekusa, H., and Ohashi, Y. (2002) Crystalline-state... 

Solid-state photochemistry absolute asymmetric oxetane synthesis from an achiral acyclic imide using die chiral crystal environment, J. Org. Chem., 58, 3476-3477. (b) Sakamoto, M., Takahashi, M., Fujita, T.,... 

In an example of solid-state photochemistry, an unexpected exo-selective formation of bicydic oxetane was reported by Kang and Scheffer (Scheme 7.29) [47]. When a solid-state ketone was irradiated using a medium-pressure Hg lamp, via a Pyrex filter (>290 nm), the exo-selective oxetane formation of oxetane was predominant (yield 91%). In acetonitrile-solution photochemistry, the radical coupling product (43%) was the only isolable product. 

The solid state photochemistry of trans-Q rm m Q acid illustrates the similarity in the nature of the control exerted by the crystal and the protein. In the crystal as in the protein the reactant molecules are preorganized. The photobehavior of ra 7s-l,2-to(4-pyridyl)ethylene further highlights this analogy [102]. rra -l,2-Z w(4-pyridyl)ethylene upon irradiation in solution,... 

A comparison of the solid state photochemistry of two crystals, 7-methoxycoumarin and methyl m-bromo-cinnamate, further exemplifies the importance of the existence of free volume near the reaction site (Sch. 15) [127-129], In spite of the fact that the reactive double bonds are rotated by 65° with respect to each other and a center-to-center double-bond distance of 3.83 A (Fig. 16), photodimerization occurs in crystals of 7-methoxy-coumarin to give the syn head-to-tail isomer (Sch. 15). On the other hand, methyl m-bromo-cinnamate, which also has a nonideal arrangement of the... 

Schmidt GMJ, et al. In Ginsburg D, ed. Solid State Photochemistry. New York Verlag Chemie, 1976. 

Cinnamates occupy an important place in the history of photochemistry. Schmidt and his co-workers [18] used the solid state photochemistry of cinnamic acid and its derivatives to develop the idea of topochemical control of photochemistry in the crystalline state. Minsk [19] developed poly(vinyl cinnamate) as the first polymer for photoimaging. The cinnamate chromophore is still commonly incorporated in photopolymers of all types, including LC polymers, to enable them to be photochemically cross-linked [20], and a number of reports of the photochemistry of such MCLC and SCLC polymers are summarized below. 

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