We examined the rotational isomerization of 9,9'-bianthracene (Figures and), which has been discussed in ref 18. Interestingly, the FB-ENM path obtained in the present study After passing through a structure where the two anthryl groups are parallel (Figure center), the green half of the upper anthryl group moves to the front side of the lower anthryl group (Figure right). Finally, the rotational isomerization completes, reaching the structure in Figure .