Differences in the parameters of pre organization of chalcone podands to intermolecular photoinduced [2+2] cycloaddition (PCA) in crystals were discovered. As a result of PCA, the chalcone podand with two oxyethylene units forms stereoregular cyclobutane containing poly mer chains over the whole volume of the single crystal. In the case of the chalcone podand with one oxyethylene unit, the PCA reaction in single crystal becomes impossible; however, its mechanical destruction results in the formation of surface layers with stacking dimers. In these layers, photodimerization occurs due to a decrease in topochemical control from the molecular lattice.The use in polymer synthesis of methods and prin ciples of supramolecular chemistry, such as self assem bling of highly ordered structures in single crystals, is one of the promising trends in the production of novel mate rials capable of demonstrating unique physicochemical properties. 1-4 For instance, polyfunctional compounds with photocontrolled groups (vinyl, styryl, cinnamoyl, anthryl, etc.) capable of reacting in stereospecific topo chemical reactions of [2π+2π] and [4π+4π] photocyclo addition (PCA) and others are used in the synthesis of linear polymers of stereoregular structure. 5-9 These processes are directly controlled by the crystal lattice providing the maximum approach of parallel photosensi tive double bonds to the distance that does not exceed 4.2 Å. 5,10-12 The studies of the photochemical transfor mations of olefins in crystals showed that photopoly merization is most characteristic of conjugated dienes with the СН=СН groups in the para position of the (hetero) aromatic ring. 5 Photopolymerization in single crystals depends to a considerable extent on the nature of photo sensitive terminal groups of the reacting molecules. On going from conjugated dienes with styryl or acrylate ter minal groups to cinnamates, the polymerization direction shifts to photodimerization with the side formation of small amounts of oligomers (n = 3, 4). 13,14It is rather difficult to attain crystal structure retention during the PCA, i.e., to retain topochemical control of the reaction course until its completion. The solution of this problem was proposed for particular classes of olefins, e.g., styryl dyes. 15-18 The main approach is the creation of loose region in the crystal structure due to the inclusion into the structural units (molecules or molecular ions) of conformationally mobile groups, solvate molecules, or rotationally mobile counterions.Combination of photosensitive groups with the con formationally mobile polyoxyethylene spacer in one molecule also could result in the appearance of loose regions in crystals. The loose regions surround the dimeric π stacking fragments preorganized to the PCA. However, attempts to carry out solid phase PCA reactions in the series of olefinic compounds, such as podands in which pairs of ditopic ligands are separated by polyether chains, were unsuccessful. 19,20 In our X ray diffraction study of the aryl containing chalcone pod...
