Role of Ring Ortho Substituents on the Configuration of Carotenoid Polyene Chains.

The 9-(Z)-configuration was exclusively obtained in the carotenoid polyene chain irrespective of olefination and disconnection methods for terminal ortho-unsubstituted benzene rings. The 2,6-dimethyl substituents in the terminal rings secure an all-(E)-polyene structure. The single molecular conductance of the pure 9-(Z)-carotene was measured for the first time to be 1.53 × 10-4 ± 6.37 × 10-5G0, whose value was 47% that of the all-(E)-carotene ((3.23 × 10-4) ± (1.23 × 10-4) G0).