Diacetylene crystal structure

The two-step process of epitaxial polymerization has been applied to symmetrically substituted diacetylenes First, the monomers have been crystallized epitaxially on alkali halides substrates from solution and the vapor phase. The oriented monomer crystals are then polymerized under the substrate s influence by gamma-irradiation. The diacetylenes in this study are 2,4-hexadiyn-l,6-diol (HD) and the bis-phenylurethane of 5,7-dodecadiyn-l,12-diol (TCDU). The polydiacetylene crystal structures and morphologies have been examined with the electron microscope. Reactivity and polymorphism are found to be controlled by the substrate. 

Fig. 32 (a) Topochemical polymerization mechanism for a typical diacetylene monomer, (b) Crystal structure of a typical poly diacetylene... 

Fully conjugated and fully chain-aligned polymer single crystals with planar polymer backbone are obtained, which may have the alternative acetylene (ynene) or butatriene structures of Eq. (1). From our experiment we know that the acetylene structure is dominant in the polymer molecules. Up to now the best investigated diacetylene crystals are the TS-6 monomer crystals and the corresponding polymer crystals (poly TS-6). The substituents R and the notation of further diacetylene crystals discussed below are listed in Table 1. 

In all experiments described in this work only extremely low concentrations of intermediates are considered. This is due to our interest which is primarily focussed on the most important initial steps of the polymerization reaction, which are characteristic of the overall polymerization reaction mechanism. Consequently only low final polymer conversion is exp>ected and, therefore, complications arising from the interaction between the intermediate oligomer states can be neglected. It will be shown that the low temperature conventional optical absorption and ESR spectroscopy are powerful spectroscopic methods which yield a wealth of information concerning structural and dynamical aspects of the intermediate states in the photopolymerization reaction of diacetylene crystals. Therefore, this contribution will center on the photochemical and photophysical primary and secondary processes of this... 

RC = C=C=CR-]-, which have the same total number of c- and jt-bonds. An energy difference of about 0.4 eV per unit easily could explain the observed structural change at about n = 6. This butatriene-to-acetylene transformation has been observed also in the TS-12 and TCDU diacetylene crystals at about the hexamer unit. 

In this article it has been shown, that the low temperature photopolymerization reaction of diacetylene crystals is a highly complex reaction with a manifold of different reaction intermediates. Moreover, the diacetylene crystals represent a class of material which play a unique role within the usual polymerization reactions conventionally performed in the fluid phase. The spectroscopic interest of this contribution has been focussed mainly on the electronic properties of the different intermediates, such as butatriene or acetylene chain structure, diradical or carbene electron spin distributions and spin multiplicities. The elementary chemical reactions within all the individual steps of the polymerization reaction have been successfully investigated by the methods of solid state spectroscopy. Moreover we have been able to analyze the physical and chemical primary and secondary processes of the photochemical and thermal polymerization reaction in diacetylene crystals. This success has been largely due to the stability of the intermediates at low temperatures and to the high informational yield of optical and ESR spectroscopy in crystalline systems. 

In Fig. 5 the values of the packing parameters d and d> are plotted for constant separations R between the reacting atoms Cl and C4. The relevance of the model considerations can be tested using crystal structure data, which have become available recently for a number of reactive and unreactive diacetylene monomers. Reactivity is only observed in a small area of the map. The distribution of the points for highly reactive structures suggest the criterion for which the separation R should be less than 4 A to be a more critical condition than the requirement of a least motion pathway as calculated by Baughman Figure 5 shows that all but one reactive diacetylene... 

Until 1977 no crystal structure analyses were known for highly reactive diacetylene monomers. Polymerization in the primary x-ray beam proceeds in these cases so rapidly that data collection on the monomer crystal is impossible. This experimental difficulty was overcome by carrying out the data collection at low temperatures. At 110 K the polymerization rate is sufficiently low to maintain a polymer content at below 5 percent during the time necessary to collect the data for an average structure. The first monomer crystal structure which was solved using this technique was PTS... 

A polymerizing diacetylene crystal can be considered as a composite material with large differences in the mechanical properties of both components. In such a material the mechanical properties will not only depend on the relative amount of the components but also very strongly on the geometrical arrangements of the structural elements Two limiting cases can be considered The first model consists... 

A necessary and sufficient condition for the formation of substitutional solid solutions of organic molecules is similarity of shape and size of the component molecules, For the formation of a continuous series of solid solutions the crystal structures of the pure components must be isomorphous Due to the rather irregular shape of organic molecules the principle of close packing leads to structures of low symmetry so that the latter requirement is not often fulfilled. Several diacetylenes which were found to form mixed crystals are given in Table 5. A large number of... 

The topochemical polymerization of diacetylenes proceeds with retention of molecular packing of the crystal structure. The reactivity strongly depends on... 

The following discussion will briefly review the available Information on the synthesis, physical properties, crystal structure, solid state reaction, and chromic behavior of these polyfunctlonal diacetylenes. 

Many aspects of the preparation and properties of polydiacetylenes are the subject of lively debate. This review presents recent results that bear on some of these controversies. First the relationship of diacetylene monomer crystal structure and solid-state reactivity is discussed. Secondly the temporal evolution of solvato-chromio transitions of soluble polydiacetylenes is displayed. Optical and Raman spectra reveal the occurrence of an intermediate form of the polymer. A model compatible with these results is described. 

Figure 2.3.11 Ball-and-sticl< representations of the crystal structures of co-crystals of diacetylene derivatives involving (a) a dicarboxylic acid host (b) a bis(pyridine) host.

Another approach is cocrystallization of a substituted urea (host) and a diacetylene (guest) [48]. Substituted ureas are used to prepare layered diacetylene crystals. Two examples are shown in Scheme 21. Such a host-guest/cocrystal approach to supramolecular synthesis should be general. In this strategy, the host is used to control the structure and the guest provides the function (optical, electrical, chemical, or physical). 

A munber of surface-confined reactions require a highly ordered prearrangement of the reactive species. The topochemical polymerization of diacetylenes is such a text book example. A critical aspect is the ordering of the diacetylene monomers, both with respect to the distance and the orientation. On the basis of the 3D crystal structures of numerous diacetylene monomers... 

Fig. 1.10 The crystal structure of macroscopic poly-diacetylene paratoluylsulfonyl-...

The crystal structures of the diacetylenes have been determined for many substituents R. A prominent example is shown in Fig. 2.20, which gives a section... 

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