Crystalline state, photoreactivity

The surrounding atmosphere generally does not show any significant effect on the crystalline state photoreaction, except a few cases which have been reported recently29,30) (see Sect. VII.). 

Crystalline-State Photoreactions Direct Observation of Reaction Processes and Metastable Intermediates... 

Y. Ohashi, Crystalline State Photoreactions Direct Observation of Reaction Processes and MetastaMe Intermediates, DOI 10.1007/978-4-43l-54373-2 l, Springer Japan 2014... 

Nakanishi, E, Nakanishi, H., Tasai, X, Suzuki, Y., and Hasegawa, M., Water participation in the crystalline state photoreaction, photodimerization of p-formylcinnamic acid, Chem. Lett., 525, 1974. 

The photoreaction of 2,3-distyrylpyrazine (2,3-DSP) derivatives has been investigated in the crystalline state (Tsutsumi et al., 1991 Takeuchi et al., 1993). On photoirradiation, 2,3-di(4-chlorostyryl)pyrazine and 2,3-di(4-cyanostyryl)pyrazine crystals give eight-membered [2.2]orthocyclophanes in 76 and 56% yields, respectively (Scheme 14). On the other hand, 2,3-DSP and 4-nitro or 4-methyl derivatives of 2,3-DSP are photostable in the crystalline state. These results are reasonably interpreted on the basis of X-ray crystallographic analysis of these crystals. 

Photoisomerization of the azobenzene amphiphile was found to be strongly affected by molecular packing and orientation in the aqueous bilayer solutions. A rate constant of trans to cis isomerization was extremely faster in the liquid crystalline state than in the crystalline bilayer membrane [33]. Photoreaction of the aqueous bilayer membrane of CgAzoCioN+ Br was... 

Triisopropylthiobenzophenone 20a and its p-methoxy derivative 20b were chosen for study (Scheme 11). Like thiobenzophenone, thiones 20 show well-separated absorption maxima in the visible (600 nm, nTi" ) and UV (320 nm, Tm" ) regions of the spectrum. In contrast, photolysis of freeze-pump-thaw-deoxygenated solutions of thiones 20a and 20b in benzene through Pyrex (>290 nm) afforded excellent chemical yields (ca. 70%) of the benzocyclo-butenethiol derivatives 21a and 21b. The same photoreaction could be brought about in the crystalline state at a much-reduced rate. 

A great number of olefinic compounds are known to photodimerize in the crystalline state (1,2). Formation of a-truxillic and / -truxinic acids from two types of cinnamic acid crystals was interpreted by Bernstein and Quimby in 1943 to be a crystal lattice controlled reaction (5). In 1964 their hypothesis on cinnamic acid crystals was visualized by Schmidt and co-workers, who correlated the crystal structure of several olefin derivatives with photoreactivity and configuration of the products (4). In these olefinic crystals the potentially reactive double bonds are oriented in parallel to each other and are separated by approximately 4 A, favorable for [2+2] cycloaddition with minimal atomic and molecular motion. In general, the environment of olefinic double bonds in these crystals conforms to one of three principal types (a) the -type crystal, in which the double bonds of neighboring molecules make contact at a distance of -3.7 A across a center of symmetry to give a centrosymmetric dimer (1-dimer) (b) the / -type crystal, characterized by a lattice having one axial length of... 

Based on some interesting reactions in certain inorganic crystalline compounds, Kohlschutter [9,10] proposed that the nature and properties of the products obtained take place on the surface or within the solid state. Indeed, he coined the term topochemistry for such reactions in the solid state. However, systematic investigations of photoinduced reactions in crystals began from 1964 onward by Schmidt and Cohen [11], Their studies on the 2tt + 2tt photoreaction of cinnamic acid derivatives in the crystalline state and correlation with the molecular organization in these crystals led to what are now known as Topochemical Principles. The most important conclusions reached by them are as follows (1) The necessary conditions for the reactions to take place are that the reactive double bonds are parallel to one another and the center-to-center distance be within 4.1 A (2) there is one-to-one correspondence between the stereochemistry of the photoproduct and the symmetry relationship between the reactants. The centrosymmet-ric relationship (called the a-form) leads to centrosymmetric cyclobutane (anti-HT), whereas the mirror symmetric arrangements (called the (5-form) produce mirror symmetric dimer (yy -HH). 

The second example is photochemical reaction of 2-benzoylbenzothioesters 57 in the chiral crystalline environment. Solid-state photoreactions of, S -(o-tolyl),. S -phcnyl, and S-(ff)-tolyl) 2-benzoylbenzothioates 57a-c, which formed chiral crystals by spontaneous resolution, underwent an intramolecular cyclization involving phenyl migration to afford the corresponding optically active 3-phenyl-3-(arylthio)phthalide 58a-c in good chemo- and enantio-selectivities. (Scheme 11). [34]... 

Sakamoto, M., Takahashi, M., Mino, T., and Fujita, T. (2001) Absolute asymmetric (3-lactam synthesis via the solid-state photoreaction of acyclic monothioimides and the reaction trajectory in the chiral crystalline environment, Tetrahedron, 57, 6713-6719. 

According to mechanism (III) even if the concentration of A in one of the two sites (7) is much smaller than the amount in site X, appreciable photoreaction from AY may occur through AxA Y energy transfer as outlined in Sch. 21 or if the quantum yield of reaction from A Y is much larger than that from A x. An example in which situation (III) operates is the photodimerization of 9-cyanoanthracene in the crystalline state presented above (Sch. 23) [138,139]. On a statistical basis, many more molecules within the crystalline bulk phase are expected to be excited than those at defect sites. However, the reaction cavities capable of supporting reaction are specific to defect sites. Efficient photodimerization is believed to occur from exciton migration from the inert bulk sites to the defect sites. 

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