Conjugated polydiacetylenes

It was found that soUd-state polymerization of these monomers always proceeds by 1,4-addition. Furthermore, polydiacetylene 96 could be thermally reacted and the structure of the final polymer was proposed to be that of the ladder polymer 97 where the repeating unit is l,6-didehydro[10]annulene (98), i.e. two conjugated polydiacetylenes. However, the annulene 98 is expected to be unstable. In fact, its cycloaromatization reaction to the... 

Jung, K., Kim, T.W., Park, H.G., and Sob, H.T. 2010. Specific clorimetric detection of proteins using bidentate aptamer-conjugated polydiacetylene (PDA) liposomes. Adv. Funct. Mater. 20 3092-3097. 

For third order nonlinear application, however, it is the concentration of the NLO dye that is of paramount importance, not the orientational aspects. The third order response is typically dependent on the extent and nature of electronic conjugation. Polydiacetylene, for example, shows very high because of the delocalized electronic structure along the n-conjugated polymer chains. The large dye molecules posses quite reasonable molecular hyperpolarizability. A high concentration of these dyes without a concomittant deterioration of linear optical properties can lead to useful bulk third order NLO coefficients. 

In this chapter, a detailed description is given of these intriguing optical properties of certain polythiophene derivatives, and their analogy with chromic effects found in other 7r-conjugated (polydiacetylenes) and or-conju-gated polymers (polysilanes) is discussed. In order to explain these transitions, various molecular mechanisms are described. Finally, potential applications of these interesting optical effects are presented. 

Figure 9.13 presents an example for the action spectrum of intrinsic photoconduction, i.e., a plot of the number of charge carries produced pw absorbed photon, for a Jt-conjugated polydiacetylene crystal (DCH). There is no photoresponse at the... 

Rotations around torsional barriers induce changes in chain conformation. For conjugated systems like polydiacetylenes, flow-induced changes in chain conformation can have a profound influence on the photon absorption and electronic conductivity properties of the material [73]. Flow-induced changes in molecular conformation form the basis for several technically important processes, the best known examples are the production of oriented fibers by gel spinning [74], the compatibility enhancement [75] and the shear-induced modification of polymer morphology [76]. 

It is also shown that the electron-phonon interaction is operative in the polymerization process of the one-dimensional conjugated polymeric crystals a simple dynamical model for the polymerisation in polydiacetylenes is presented that accounts for the existing observations. 

Because of this degeneracy and coexistence of these resonant structures one expects intrinsic conjugation defects to exist and be formed along the chain, the so-called Pople-Wamsley defects (34) which in the case of polyacenes and polydiacetylenes takes the form... 

The above conclusions introduce intrinsic limitations to the use of the ID conjugated systems in nonlinear optical devices. Although these may benefit (38) from the high nonlinearities,their response speed will be limited by the motion of such defects. These may also be formed by other means than light and this will clearly have implications on photoelastic, pyroelectric and piezoelectric effects as well. We point out that materials like polydiacetylenes may show appreciable quadrupolar pyroelectric effect (39). 

The solid-state polymerization of diacetylenes is an example of a lattice-controlled solid-state reaction. Polydiacetylenes are synthesized via a 1,4-addition reaction of monomer crystals of the form R-C=C-CeC-R. The polymer backbone has a planar, fully conjugated structure. The electronic structure is essentially one dimensional with a lowest-energy optical transition of typically 16 000 cm-l. The polydiacetylenes are unique among organic polymers in that they may be obtained as large-dimension single crystals. 

Dobrosavljevic V, Stratt R (1987) Role of conformational disorder in the electronic-structure of conjugated polymers substituted polydiacetylenes. Phys Rev B 35 2781-2794... 

Polydiacetylenes are obtained as single crystals by topochemical solid-state polymerization of the monomer single crystal. These compounds have received considerable attention because of their one-dimensionally -conjugated structure. Their unique --electron structures, and therefore superior third-order nonlinear optical properties, have been extensively investigated. 

Another important step was made by Wegner who obtained crystalline polydiacetylenes of high molecular weight exhibiting a fully conjugated backbone [113]. The theory describes the electron structure of the polydiacetylenes in the frame of the ID wideband semiconductor. The polydiacetylene systems are... 

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