Topochemical photopolymerization

Cinnamic acid derivative 36 crystallizes in the chiral space group P2t and gives the optically pure dimer 37 upon irradiation in the solid state [22], Chiral crystals of 38 gave, upon irradiation, the optically active dimer 39 of 90% ee, whereas the corresponding methyl ester gave a highly crystalline linear polymer through a typical [2 + 2] topochemical photopolymerization [23],... 

X-ray structure analysis and topochemical photopolymerization of 2,5-dimethoxyphenyl-and quinone-substituted octa-3,5-diynes. Tetrahedron 2000, 56, 6781-6794. 

Enthalpy changes are derived from the peak areas of DSC curves taking the melting heat of DSP (12.0 kcal/mol) as a standard66. From the relative enthalpy levels of molten and crystalline DSP, and amorphous and crystalline poly-DSP, the topochemical photopolymerization of DSP is found to be an endothermal reaction with an enthalpy increase of about 3.7 kcal/mol. 

Hasegawa, M. (1986). Topochemical photopolymerization of diolefln crystals. Pure Appl Chem., 58, 1179-88. [236]... 

It was first reported that the topochemical photopolymerization of diolefin crystals gave rise to cracks and deformation [7]. An atomic force microscopic (AFM) study made possible the observation that the photodimerizations of trans-cinnamic acids and anthracenes in the crystalline state induced surface morphological changes at the tens and hundreds of nanometers level by the transportation and rebuilding of the surface molecules [8]. The appearance of a surface relief grating on the single crystal of 4-(dimethylamino)azobenzene was demonstrated by repeated irradiation with two coherent laser beams [9]. 

The topochemical photopolymerizations of these diolefin crystals have been reviewed in several reports (9,10). 

Lahav et al. applied the empirical rule of a topochemically photopolymeric structure (O to the unsymmetric diolefin crystals, thus succeeding in obtaining optically active dimers and oligomers through the crystallization of an achiral monomer into a chiral crystal, followed by the four-center type photopolymerization (12). 

Chart 10.7 Typical diacetylene derivatives capable of undergoing topochemical photopolymerization. Left classical examples [30]. Right Self-assembling bolaamphiphilic diacetylenes [67]. 

Chart 10.8 Structures of diradicals and dicarbenes involved in the topochemical photopolymerization of diacetylenes [32]. 

Chart 10.9 presents four other dialkenes that are amenable to topochemical photopolymerization. 

Chart 3.7 Diacetylene derivatives capable of undergoing topochemical photopolymerization [56,65]. 

Hasegawa, M., Endo, Y., Aoyama, M., and Saigo, K., Topochemical photopolymerization and photocopolymerization of the crystals of unsymmetrically substituted diolefin compounds having pyrimidine ring. Bull. Chem. Soc. Jpn., 62,1556, 1989. 

Asymmetric [2-1-2]-cycloadditions for one-component crystals have been reported. Ethyl ester 30a forms chiral crystals of P-type packing. Irradiation of the single crystals of 30a affords the optically active dimer 31 with an enantiomeric excess (EE) of >90%. In contrast, methyl ester 30b yields the highly crystalline polymer 32 through a typical [ 2-1-2]-topochemical photopolymerization. 

Direct transformation from 2,5-DSP to poly-2,5-DSP through 2,5-DSP oligomer in the crystal is shown in Scheme 1. This new reaction was named a four-centre-type photopolymerization. As well as being the first example of a topochemical reaction in a pure sense, the four-centre-type photopolymerization of 2,5-DSP crystals was the first example of photopolymerization via a step-growth mechanism. 

In the crystal of 1,4-dicinnamoylbenzene (1,4-DCB) (see Fig. 12), the distances between the intermolecular photoadductive carbons are 3.973 and 4.086 A for one cyclobutane ring, and 3.903 and 3.955 A for the other. The two topochemical pathways may occur competitively in a single crystal of 1,4-DCB at the initial stage of reaction. Then, both intramolecular photodimerization and intermolecular photopolymerization of the diolefinic mono-cyclobutane intermediate occur competitively to give tricyclic dimer 21,22,23,24-tetraphenyl-l,4,ll,14-tetraoxo-2(13),12(13-diethanol, [4.4] para-cyclophane or oligomers (Hasegawa et al., (1985). On photoirridation at room temperature the 1,4-DCB crystal gives >90% of the tricylic... 

The synthesis of cis-1,4 polymers was also tried by e use of monomers with an s-cis conformation. The solid-state photopolymerization of pyridone derivatives, which is a six-membered cyclic diene amide and is a tautomer of 2-hydroxypyridine, was attempted [100]. Pyridones make hydrogen-bonded cocrystals with a carboxylic acid in the crystalline state. Because the cyclic structure fixes its s-cis conformation, if the polymerization proceeds, a cis-2,5 polymer would be obtained. Actually, however, the photopolymerization did not occur, contrary to our expectation, but [4-1-4] photodimerization proceeded when the carbon-to-carbon distance for the dimerization was small (less than 4 A) [101]. A closer stacking distance of the 2-pyridone moieties might be required for the topochemical polymerization of cychc diene monomers. 

Fang G, Javier M-R, Zhigang P, Colan EH, Kenneth DMH (2008) Direct structural understanding of a topochemical solid state photopolymerization reaction. J Phys Chem C 112 19793-19796... 

Diacetylene monolayer photopolymerization was found to be topochemical it only occurred in the two-dimensional solid state of the surfactants. Polymerized diacetylenes, both in monolayers and in LB films, were found to be rather rigid and prone to cracking [160]. This undesirable property somewhat limits the exploitation of polymerized diacetylene LB films for potential electronic applications. 

At present, it is common knowledge that not only the photoreactivity, but also the stereochemistry, of the photoproduct is predictable from crystallographic information of starting olefin substrates. This ability of olefinic crystals to dimerize has been widely applied to the topochemical photocycloaddition polymerization of conjugated diolefinic compounds, so called "four-center type photopolymerizations" (7,8). All the photopolymerizable diolefin crystals are related to the center of symmetry mode (centrosymmetric -type crystal) and thus give polymers having cyclobutanes with a 1,3-trans configuration in the main chain on irradiation. 

Only a few review articles concerning this type of topochemical polymerization have been published so far8,11 from the viewpoint of a specific field, though extensive work has been done in recent years. This article is the first review of a four-center photopolymerization and related problems which covers all the results obtained from a variety of... 

This is a striking example of a matrix effect originating in the topochemical process of a substance which is chemically the same (oligomer) but behaves in three different ways photodepolymerization, photopolymerization, and no photoreaction, depending on its physical state (in solution, in as-prepared and recrystallized crystalline states)33. Further discussions on the matrix effect have been made in correlation with crystallographic studies (see Sect. IV.b. and VII.). 

In conclusion, the four-center photopolymerization is a novel type of topochemical reaction which is crystal-lattice controlled with respect to the whole set of elementary processes44 including initiation, propagation and crystallization of polymer. 

Based on the results of crystalline-state depolymerization, a reversible topochemical process, which is a monomer crystal lattice-controlled photopolymerization and a polymer crystal lattice-controlled thermal depolymerization, is established65. ... 

As a suitable reaction we selected 2n + 2n) photocycloaddition as demonstrated by Schmidt, disubstituted ethylenes, appropriately oriented in the crystal and with the double bonds at a distance 4 A, form on u.v. irradiation cyclobutane dimers with a stereochemistry that directly reflects the symmetry relating the monomers in the mother phase (topochemical dimerization). Subsequently, Hasegawa and Naka-nishi have demonstrated that, when the double bonds are appropriately oriented and spaced, symmetrical disubstituted / -distyryl derivatives undergo, by the same mechanism, topochemical solid-state photopolymerization. 

The first example of crystalline state [2-1-2] photocycloaddition polymerization was the reaction of 2,5-distyrylpyradine (DSP) crystal, discovered in 1967. This polymerization proceeds under the strict control of the reacting crystal lattice throughout the course of reaction it was named the "four-center type photopolymerization" ( ). The polymerization of DSP crystal was the first example of photopolymerization by a step-by-step mechanism as well as of topochemical polymerization. 

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