Helicity-Controlled Liquid Crystal Reaction Field Using Nonbridged and Bridged Binaphthyl Derivatives Available for Synthesis of Helical Conjugated Polymers

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Abstract

The nonbridged and bridged type axially chiral binaphthyl derivatives were synthesized and used as chiral dopants to prepare chiral nematic liquid crystals (N*-LCs) available for an asymmetric reaction field producing helical conjugated polymers. The bridged structure has a linkage between the 2 and 2‘ positions of the binaphthyl rings through a tetramethylene chain. It is found that the conformation of the nonbridged binaphthyl derivative in an N-LC solvent is different from that in an isotropic one, giving a different helicity in both solvents, although its configuration remains unchanged. Namely, the nonbridged binaphthyl derivative exhibits transoid (meta-stable) and cisoid (most stable) conformations in N-LC and isotropic solvents, respectively. Meanwhile, the bridged binaphthyl derivative forms a cisoid conformation irrespective of solvent, as expected by the strictly restricted internal rotation of the binaphthyl rings. As a consequence, the nonbridged and bridged binaphthyl derivatives, both of which have an (R)-configuration, take a P-helicity due to the transoid conformation and an M-helicity due to the cisoid one in N-LCs, respectively. This leads to oppositely screwed N*-LCs when these binaphthyl derivatives are added as chiral dopants into N-LCs, though they have the same configuration. Concomitantly, helical polyacetylenes synthesized in the N*-LCs also have oppositely screwed structures in fibril bundles. The usage of the nonbridged and bridged binaphthyl derivatives, as chiral inducers having the same configuration but the opposite helical sense, affords a convenient and promising way to construct the helicity-controlled LC reaction field.

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