Optically active carbazole containing monomers

Optically active polymers containing carbazole groups may be synthesised by polymerisation of intrinsically optically active carhazole-containing monomers or by copolymerisation of a variety of optically active co-monomers with nonchiral carbazole-containing monomers. Full details are given and it is concluded that the second method is most useful, not least because it permits a wider variation in polymer backbone structures. V. V. absorption fluorescence emission, NMR, and circular dickroism spectra are reported in detail and help to establish a correlation between photophysical behaviour widi both primary and secondary structural features of the polymers. 

The synthetic approach to optically active polymers based on the copolymerization of prochiral carbazole containing monomers with easily available optically active vinyl or vinylidenic comonomers is by far the most convenient route to a large variety of optically active polymers. Accordingly, N-vinylcarbazole and spaced-carbazole containing vinyl monomers 11-14 have been copolymerized with different optically active monomers 15-20. 

Table 4. General properties of copolymers of unsaturated carbazole-containing monomers with optically active comonomers obtained in the presence of different initiators...

Cyanophenyl)-[3-[9-[2-(2-methacryloyloxy-propanoyloxyethyl] carbazolyl]] diazene [(5)-MLECA] chiral monomer containing the carbazole moiety is a novel optically active photochromic polymer. After study of chiroptical, thermally and spectroscopic properties shows the presence of dipolar interaction characteristics between chromophores and chiral confirmation of prevailing helical hardness for chain segments of macromolecules. 

Essentially there are two major ways in which optical activity may be introduced into synthetic polymers. Most obviously the synthesis and utilization of inherently chiral monomers may be employed. Alternatively, and perhaps more conveniently, a prochiral monomer may be copolymerized with a suitable chiral comonomer. For carbazole-containing polymers both synthetic approaches have been employed. 

In copolymers of NVC with different optically active comonomers a definite contribution derived from the prochiral monomer to the molar optical rotation of the whole polymer, is more or less clearly obtained (Fig. 1). In copolymers containing the carbazole moiety spaced far apart from the polymer backbone no apparent contribution is evidenced. More detailed features of any preferentially dissymmetric conformational structure of the carbazole moieties can be gained through circular dichroism measurements . ... 

Rather unusually, induced circular dichroism in copolymers of N-vinylcarbazole with different optically active monomers is optimized at particular copolymer compositions and hence offers an obvious route to the design of optically active polymer reagents from N-vinylcarbazole. Analogously, the dependence of excimer emission properties in carbazole-containing polymers on the primary structure of the monomeric units and the microstructure of the polymer backbone offers the possibility to design polymeric systems with predictable photoresponses and energy transfer characteristics. 

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