One of the ultimate research goals of materials science would be the construction of molecular machines, where one molecule mechanically works as a machine by external energy sources. Recently we have first succeeded in the construction of a light-powered chiral molecular motor, which photochemically rotates only in one-direction reflecting the chirality of the motor molecule. The motor rotation is also controlled by the “ratchet effect” due to the irreversible isomerization. In this paper, we account for the unique chemistry of motor molecules, chiral and helical olefins of 1,1′,2,2′,3,3′,4,4′-octahydro-3,3′-dimethyl-4,4′-biphenanthrylidene (E)-(3) and (Z)-isomer (4), and also report the irreversible thermal isomerization of unstable (3R,3′R)-(M,M)-(E)-3 to stable (3R,3′R)-(P,P)-(E)-(−)-3, which works as the “ratchet effect” of the motor. The stereochemistry and rotation mechanism of the motor are explained.
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