posted on 2021-03-05, 14:07authored byKirill Nikitin, Yannick Ortin, Michael J. McGlinchey
Directional
internal rotation in molecular systems, generally controlled
by chirality, is known to occur in natural and artificial systems
driven by light or fueled chemically, but spontaneous directional
molecular rotation is believed to be forbidden. We have designed a
molecular rotor, whereby ferrocene and triptycene linked by a methylene
bridge provide two rotational degrees of freedom. On the basis of
experimental observations, in conjunction with computational data,
we show that the two different modes of rotation are strongly coupled
and the spatial orientation of the bistable ferrocene moiety controls
the barrier to its own rotation about the triptycene axis. It is proposed
that the barrier to clockwise 120° rotation across each individual
triptycene blade is lower in the M-enantiomer and
for counterclockwise 120° rotation, it is lower in its P-counterpart. These findings demonstrate the possibility
of locally preferred thermal directional intramolecular rotation for
each dynamically interconverting enantiomer.