The synthesis and physical properties of pyranobenzopyran ring system have been studied as a core structure of novel liquid crystal (LC) compounds. Substituted pyranobenzopyrans having an alkoxy group on the A ring (benzene ring) exhibited smectic and nematic phase, those having a fluoro-substituted phenyl group on the A ring exhibited wider range of smectic phase. When the latter are added to a base LC mixture (ZLI-1565, Merck), the clearing point was raised. Interestingly, pyranobenzopyrans having a trifluoromethyl phenyl group or a cyano group on the A ring showed an extremely large positive dielectric anisotropy.
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