Cotton effects polyacetylenes

A cast film of 28 also responded to the chirality of liquid and solid chiral amines, and exhibited an ICD in the UV-visible region. The observed Cotton effect patterns were similar to those of 28 induced by the chiral amines in solution [147]. These methods are more convenient and practically feasible to sense the chirality of chiral amines than the solution method, and may be applicable to other dynamic helical polyacetylenes. 

In circular dichroism (CD) spectra of the polyacetylene thin films synthesized under the (fi-2)- and (S-2)-chiral nematic LCs, positive and negative Cotton effects are observed, respectively, in the region from 450 to 800 nm corresponding to tt — it transition of polyacetylene chain (Figure 3.8), despite the absence of chiroptical substituent in side chains. This indicates that the polyacetylene chain itself is helically screwed. It is evident that the above Cotton effect is not due to the chiral dopant [( )- or... 

Helical polyacetylene was synthesized in asymmetric reaction field consisting of chiral nematic LC. The chiral nematic LC was prepared by adding a chiroptical binaphthyl derivative as a chiral dopant to a mixture of two nematic LCs. Acetylene polymerizations were carried out using the catalyst Ti(0-n-Bu)4— EtsAl dissolved in the chiral nematic LC solvent. The polyacetylene film consisted of clockwise or counterclockwise helical structure of fibrils in SEM. Cotton effect was observed in the region of ir — ir transition of the polyacetylene chain in CD spectrum. The high-electrical conductivities of 1.5 1.8 x... 

Figure 4. Solvent dependence of the first Cotton effect (X ax nm) of the polyacetylenes bearing pendants of L-amino acid methyl esters.

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