Optically active carbazole 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. 

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. 

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. 

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 . ... 

The very attractive synthetic procedure based on the use of optically active initiators that has been successfully applied to the polymerization of unsaturated monomers bulkier than carbazole °, does not seem to offer any value in the synthesis of optically active polymers from carbazole monomers, at least in the case of polymerization of... 

Introduction of the carbazole group to the optically active matrix does not appreciably affect the molar optical rotation of the starting polymer and an overall dilution effect has been achieved analogous to that observed in polymeric products obtained by direct copolymerization of optically active monomers with (9-carbazolyl)-methyl styrenes 11 and 12 >. 

Similarly, in copolymers of chiral monomers with monomers having carbazole spaced from the main chain there is a much lower induced optical activity. This effect operates even when carbazole is spaced from the main chain by the relatively rigid benzyl group, as in copolymers from 11 and 12 with optically active monomers... 

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

Optically active monomer Carbazole monomer Catalyst Polymeric product Ref. 

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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